publications.bib

@article{Helmuth:2021:ALifeJournal,
  author = {Thomas Helmuth and Lee Spector},
  title = {Problem-solving benefits of down-sampled lexicase selection},
  journal = {Artificial Life},
  year = {2021},
  note = {In press},
  doi-url = {},
  url = {},
  pdf = {https://arxiv.org/pdf/2106.06085.pdf}
}
@article{Helmuth:2020:GPEM,
  author = {Thomas Helmuth and Edward Pantridge and Lee Spector},
  title = {On the importance of specialists for lexicase selection},
  journal = {Genetic Programming and Evolvable Machines},
  publisher = {Springer},
  year = {2020},
  volume = {21},
  number = {3},
  pages = {349--373},
  month = sep,
  note = {Special Issue: Highlights of Genetic Programming 2019
		 Events},
  keywords = {genetic algorithms, genetic programming, Lexicase
		 selection, Specialists, Parent selection, Program
		 synthesis},
  issn = {1389-2576},
  doi = {doi:10.1007/s10710-020-09377-2},
  size = {25 pages},
  abstract = {Lexicase parent selection filters the population by
		 considering one random training case at a time,
		 eliminating any individual with an error for the
		 current case that is worse than the best error of any
		 individual in the selection pool, until a single
		 individual remains. This process often stops before
		 considering all training cases, meaning that it will
		 ignore the error values on any cases that were not yet
		 considered. Lexicase selection can therefore select
		 specialist individuals that have high errors on some
		 training cases, if they have low errors on others and
		 those errors come near the start of the random list of
		 cases used for the parent selection event in question.
		 We hypothesize here that selecting such specialists,
		 which may have high total error, plays an important
		 role in lexicase selection observed performance
		 advantages over error-aggregating parent selection
		 methods such as tournament selection, which select
		 specialists less frequently. We conduct experiments
		 examining},
  doi-url = {http://dx.doi.org/10.1007/s10710-020-09377-2},
  url = {https://link.springer.com/article/10.1007%2Fs10710-020-09377-2},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2020-GPEM-lexicase-specialists.pdf}
}
@article{LaCava:2019:ecj,
  author = {William {La Cava} and Thomas Helmuth and Lee Spector
		 and Jason H. Moore},
  title = {A probabilistic and multi-objective analysis of
		 lexicase selection and epsilon-lexicase selection},
  journal = {Evolutionary Computation},
  year = {2019},
  url = {https://www.mitpressjournals.org/doi/pdf/10.1162/evco_a_00224},
  pdf = {https://arxiv.org/pdf/1709.05394.pdf},
  keywords = {genetic algorithms, genetic programming},
  issn = {1063-6560},
  doi = {doi:10.1162/evco_a_00224},
  size = {28 pages},
  abstract = {Lexicase selection is a parent selection method that
		 considers training cases individually, rather than in
		 aggregate, when performing parent selection. Whereas
		 previous work has demonstrated the ability of lexicase
		 selection to solve difficult problems in program
		 synthesis and symbolic regression, the central goal of
		 this paper is to develop the theoretical underpinnings
		 that explain its performance. To this end, we derive an
		 analytical formula that gives the expected
		 probabilities of selection under lexicase selection,
		 given a population and its behaviour. In addition, we
		 expand upon the relation of lexicase selection to
		 many-objective optimization methods to describe the
		 behavior of lexicase selection, which is to select
		 individuals on the boundaries of Pareto fronts in
		 high-dimensional space. We show analytically why
		 lexicase selection performs more poorly for certain
		 sizes of population and training cases, and show why it
		 has been shown to perform more poorly in continuous
		 error spaces. To address this last concern, we propose
		 new variants of epsilon-lexicase selection, a method
		 that modifies the pass condition in lexicase selection
		 to allow near-elite individuals to pass cases, thereby
		 improving selection performance with continuous errors.
		 We show that epsilon-lexicase outperforms several
		 diversity-maintenance strategies on a number of
		 real-world and synthetic regression problems.},
  doi-url = {http://dx.doi.org/10.1162/evco_a_00224}
}
@article{Helmuth:2015:ieeeTEC,
  author = {Thomas Helmuth and Lee Spector and James Matheson},
  title = {Solving Uncompromising Problems with Lexicase
		 Selection},
  journal = {IEEE Transactions on Evolutionary Computation},
  year = {2015},
  volume = {19},
  number = {5},
  pages = {630--643},
  month = oct,
  keywords = {genetic algorithms, genetic programming, parent
		 selection, lexicase selection, tournament selection,
		 PushGP},
  issn = {1089-778X},
  url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6920034},
  doi = {doi:10.1109/TEVC.2014.2362729},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/lexicase-IEEETEC-2014.pdf},
  size = {14 pages},
  abstract = {We describe a broad class of problems, called
		 uncompromising problems, characterised by the
		 requirement that solutions must perform optimally on
		 each of many test cases. Many of the problems that have
		 long motivated genetic programming research, including
		 the automation of many traditional programming tasks,
		 are uncompromising. We describe and analyse the
		 recently proposed lexicase parent selection algorition
		 and show that it can facilitate the solution of
		 uncompromising problems by genetic programming. Unlike
		 most traditional parent selection techniques, lexicase
		 selection does not base selection on a fitness value
		 that is aggregated over all test cases; rather, it
		 considers test cases one at a time in random order. We
		 present results comparing lexicase selection to more
		 traditional parent selection methods, including
		 standard tournament selection and implicit fitness
		 sharing, on four uncompromising problems: finding terms
		 in finite algebras, designing digital multipliers,
		 counting words in files, and performing symbolic
		 regression of the factorial function. We provide
		 evidence that lexicase selection maintains higher
		 levels of population diversity than other selection
		 methods, which may partially explain its utility as a
		 parent selection algorithm in the context of
		 uncompromising problems.},
  notes = {also known as \cite{6920034}},
  doi-url = {http://dx.doi.org/10.1109/TEVC.2014.2362729}
}
@inproceedings{Helmuth:2021:GECCO:PSB2,
  author = {Thomas Helmuth and Peter Kelly},
  title = {{PSB2}: The Second Program Synthesis Benchmark Suite},
  booktitle = {2021 Genetic and Evolutionary Computation Conference},
  series = {GECCO '21},
  year = {2021},
  isbn13 = {978-1-4503-8350-9},
  address = {Lille, France},
  size = {10 pages},
  doi = {10.1145/3449639.3459285},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  month = {10-14} # jul,
  doi-url = {https://doi.org/10.1145/3449639.3459285},
  url = {https://dl.acm.org/doi/10.1145/3449639.3459285},
  pdf = {https://arxiv.org/pdf/2106.06086.pdf},
  associated = {https://cs.hamilton.edu/~thelmuth/PSB2/PSB2.html},
  note = {\textbf{Nominated, Best Paper Award, Genetic Programming Track}}
}
@inproceedings{Helmuth:2020:ALife:downsampledlexicase,
  author = {Helmuth, Thomas and Spector, Lee},
  title = {Explaining and Exploiting the Advantages of Down-sampled Lexicase Selection},
  booktitle = {Artificial Life Conference Proceedings},
  publisher = {MIT Press},
  pages = {341-349},
  month = {13-18 } # jul,
  year = {2020},
  doi = {10.1162/isal_a_00334},
  url = {https://direct.mit.edu/isal/proceedings/isal2020/32/341/98485},
  pdf = {https://direct.mit.edu/isal/proceedings-pdf/isal2020/32/341/1908528/isal_a_00334.pdf},
  video = {https://youtu.be/IR14htbTatg},
  abstract = { In genetic programming, parent selection is ordinarily based on aggregate measures of performance across an entire training set. Lexicase selection, by contrast, selects on the basis of performance on random sequences of test cases; this has been shown to enhance problem-solving power in many circumstances. Lexicase selection can also be seen as better reflecting biological evolution, by modeling sequences of challenges that organisms face over their lifetimes. Recent work has demonstrated that the advantages of lexicase selection can be amplified by down-sampling, meaning that only a random subsample of the training cases is used each generation, which can also be seen as modeling environmental change over time. Here we provide the most extensive benchmarking of down-sampled lexicase selection to date, showing that its benefits hold up to increased scrutiny. The reasons that down-sampling helps, however, are not yet fully understood. Hypotheses include that down-sampling allows for more generations to be processed with the same budget of program evaluations; that the variation of training data across generations acts as a changing environment, encouraging adaptation; or that it reduces overfitting, leading to more general solutions. We systematically evaluate these hypotheses, finding evidence against all three, and instead draw the conclusion that down-sampled lexicase selection's main benefit stems from the fact that it allows GP to examine more individuals within the same computational budget, even though each individual is examined less completely. }
}
@inproceedings{Helmuth:2020:ALife:source,
  author = {Helmuth, Thomas and Pantridge, Edward and Woolson, Grace and Spector, Lee},
  title = {Genetic Source Sensitivity and Transfer Learning in Genetic Programming},
  booktitle = {Artificial Life Conference Proceedings},
  publisher = {MIT Press},
  pages = {303-311},
  month = {13-18 } # jul,
  year = {2020},
  doi = {10.1162/isal_a_00326},
  url = {https://direct.mit.edu/isal/proceedings/isal2020/32/303/98422},
  pdf = {https://direct.mit.edu/isal/proceedings-pdf/isal2020/32/303/1908486/isal_a_00326.pdf},
  video = {https://youtu.be/w1ogl2oNVgc},
  abstract = { Genetic programming uses biologically-inspired processes of variation and selection to synthesize computer programs that solve problems. Here we investigate the sensitivity of genetic programming to changes in the probability that particular instructions and constants will be chosen for inclusion in randomly generated programs or for introduction by mutation. We find, contrary to conventional wisdom within the field, that genetic programming can be highly sensitive to changes in this source of new genetic material. Additionally, we find that genetic sources can be tuned to significantly improve adaptation across sets of related problems. We study the evolution of solutions to software synthesis problems using untuned genetic sources and sources that have been tuned on the basis of problem statements, human intuition, or prevalence in prior solution programs. We find significant differences in performance across these approaches, and use these lessons to develop a method for tuning genetic sources on the basis of evolved solutions to related problems. This “transfer learning” approach tunes genetic sources nearly as well as humans do, but by means of a fully automated process that can be applied to previously unsolved problems. }
}
@inproceedings{Helmuth:2019:GECCO,
  author = {Thomas Helmuth and Edward Pantridge and Lee Spector},
  title = {Lexicase selection of specialists},
  booktitle = {GECCO '19: Proceedings of the Genetic and Evolutionary
         Computation Conference},
  year = {2019},
  noeditor = {Manuel Lopez-Ibanez and Thomas Stuetzle and Anne Auger
         and Petr Posik and Leslie {Peprez Caceres} and Andrew
         M. Sutton and Nadarajen Veerapen and Christine Solnon
         and Andries Engelbrecht and Stephane Doncieux and
         Sebastian Risi and Penousal Machado and Vanessa Volz
         and Christian Blum and Francisco Chicano and Bing Xue
         and Jean-Baptiste Mouret and Arnaud Liefooghe and
         Jonathan Fieldsend and Jose Antonio Lozano and Dirk
         Arnold and Gabriela Ochoa and Tian-Li Yu and Holger
         Hoos and Yaochu Jin and Ting Hu and Miguel Nicolau and
         Robin Purshouse and Thomas Baeck and Justyna Petke and
         Giuliano Antoniol and Johannes Lengler and Per Kristian
         Lehre},
  isbn13 = {978-1-4503-6111-8},
  pages = {1030--1038},
  address = {Prague, Czech Republic},
  doi = {doi:10.1145/3321707.3321875},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  month = {13-17 } # jul,
  organisation = {SIGEVO},
  keywords = {genetic algorithms, genetic programming},
  notes = {Also known as \cite{3321875} GECCO-2019 A
         Recombination of the 28th International Conference on
         Genetic Algorithms (ICGA) and the 24th Annual Genetic
         Programming Conference (GP)},
  doi-url = {http://dx.doi.org/10.1145/3321707.3321875},
  url = {https://dl.acm.org/citation.cfm?doid=3321707.3321875},
  pdf = {https://arxiv.org/pdf/1905.09372.pdf},
  note = {\textbf{Winner of Best Paper Award, Genetic Programming Track} (38\% acceptance rate out of 39 submissions in track, 3 best paper nominations)}
}
@inproceedings{Jundt:2019:GECCO,
  author = {Lia Jundt and Thomas Helmuth},
  title = {Comparing and combining lexicase selection and novelty
		 search},
  booktitle = {GECCO '19: Proceedings of the Genetic and Evolutionary
		 Computation Conference},
  year = {2019},
  noeditor = {Manuel Lopez-Ibanez and Thomas Stuetzle and Anne Auger
		 and Petr Posik and Leslie {Peprez Caceres} and Andrew
		 M. Sutton and Nadarajen Veerapen and Christine Solnon
		 and Andries Engelbrecht and Stephane Doncieux and
		 Sebastian Risi and Penousal Machado and Vanessa Volz
		 and Christian Blum and Francisco Chicano and Bing Xue
		 and Jean-Baptiste Mouret and Arnaud Liefooghe and
		 Jonathan Fieldsend and Jose Antonio Lozano and Dirk
		 Arnold and Gabriela Ochoa and Tian-Li Yu and Holger
		 Hoos and Yaochu Jin and Ting Hu and Miguel Nicolau and
		 Robin Purshouse and Thomas Baeck and Justyna Petke and
		 Giuliano Antoniol and Johannes Lengler and Per Kristian
		 Lehre},
  isbn13 = {978-1-4503-6111-8},
  pages = {1047--1055},
  address = {Prague, Czech Republic},
  doi = {doi:10.1145/3321707.3321787},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  month = {13-17 } # jul,
  organisation = {SIGEVO},
  keywords = {genetic algorithms, genetic programming},
  notes = {Also known as \cite{3321787} GECCO-2019 A
		 Recombination of the 28th International Conference on
		 Genetic Algorithms (ICGA) and the 24th Annual Genetic
		 Programming Conference (GP)},
  doi-url = {http://dx.doi.org/10.1145/3321707.3321787},
  url = {https://dl.acm.org/citation.cfm?doid=3321707.3321787},
  pdf = {https://arxiv.org/pdf/1905.09374.pdf}
}
@inproceedings{Helmuth:2018:GECCO,
  author = {Thomas Helmuth and Nicholas Freitag McPhee and Lee
		 Spector},
  title = {Program synthesis using uniform mutation by addition
		 and deletion},
  booktitle = {GECCO '18: Proceedings of the Genetic and Evolutionary
		 Computation Conference},
  year = {2018},
  noeditor = {Hernan Aguirre and Keiki Takadama and Hisashi Handa
		 and Arnaud Liefooghe and Tomohiro Yoshikawa and Andrew
		 M. Sutton and Satoshi Ono and Francisco Chicano and
		 Shinichi Shirakawa and Zdenek Vasicek and Roderich
		 Gross and Andries Engelbrecht and Emma Hart and
		 Sebastian Risi and Ekart Aniko and Julian Togelius and
		 S{\'e}bastien Verel and Christian Blum and Will Browne
		 and Yusuke Nojima and Tea Tusar and Qingfu Zhang and
		 Nikolaus Hansen and Jose Antonio Lozano and Dirk
		 Thierens and Tian-Li Yu and J{\"u}rgen Branke and
		 Yaochu Jin and Sara Silva and Hitoshi Iba and Anna I
		 Esparcia-Alcazar and Thomas Bartz-Beielstein and
		 Federica Sarro and Giuliano Antoniol and Anne Auger and
		 Per Kristian Lehre},
  isbn13 = {978-1-4503-5618-3},
  pages = {1127--1134},
  address = {Kyoto, Japan},
  url = {http://doi.acm.org/10.1145/3205455.3205603},
  doi = {doi:10.1145/3205455.3205603},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2018-GECCO-UMAD.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  month = {15-19 } # jul,
  organisation = {SIGEVO},
  keywords = {genetic algorithms, genetic programming},
  notes = {Also known as \cite{3205603} GECCO-2018 A
		 Recombination of the 27th International Conference on
		 Genetic Algorithms (ICGA-2018) and the 23rd Annual
		 Genetic Programming Conference (GP-2018)},
  doi-url = {http://dx.doi.org/10.1145/3205455.3205603},
  note = {\textbf{Winner of Best Paper Award, Genetic Programming Track} (37\% acceptance rate out of 30 submissions in track, 3 best paper nominations)}
}
@inproceedings{Helmuth:2017:GECCO,
  author = {Thomas Helmuth and Nicholas Freitag McPhee and Edward
		 Pantridge and Lee Spector},
  title = {Improving Generalization of Evolved Programs Through
		 Automatic Simplification},
  booktitle = {Proceedings of the Genetic and Evolutionary
		 Computation Conference},
  series = {GECCO '17},
  year = {2017},
  isbn13 = {978-1-4503-4920-8},
  address = {Berlin, Germany},
  pages = {937--944},
  size = {8 pages},
  url = {http://doi.acm.org/10.1145/3071178.3071330},
  doi = {doi:10.1145/3071178.3071330},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2017-GECCO-simplification-for-generalization.pdf},
  acmid = {3071330},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  keywords = {genetic programming, automatic
		 simplification, generalization, overfitting, Push},
  month = {15-19 } # jul,
  notes = {Also known as \cite{Helmuth:2017:IGE:3071178.3071330}
		 GECCO-2017 A Recombination of the 26th International
		 Conference on Genetic Algorithms (ICGA-2017) and the
		 22nd Annual Genetic Programming Conference (GP-2017)},
  doi-url = {http://dx.doi.org/10.1145/3071178.3071330},
  note = {\textbf{Nominated, Best Paper Award, Genetic Programming Track} (36\% acceptance rate out of 47 submissions in track, 3 best paper nominations)}
}
@inproceedings{Helmuth:2016:GECCO,
  author = {Thomas Helmuth and Nicholas Freitag McPhee and Lee
		 Spector},
  title = {The Impact of Hyperselection on Lexicase Selection},
  booktitle = {GECCO '16: Proceedings of the 2016 conference on Genetic and
		 Evolutionary Computation Conference},
  year = {2016},
  editor = {Tobias Friedrich},
  pages = {717--724},
  keywords = {genetic algorithms, genetic programming},
  month = {20-24 } # jul,
  organisation = {SIGEVO},
  address = {Denver, USA},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  isbn13 = {978-1-4503-4206-3},
  doi = {doi:10.1145/2908812.2908851},
  url = {http://doi.acm.org/10.1145/2908812.2908851},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GECCO-hyperselection.pdf},
  abstract = {Lexicase selection is a parent selection method that
		 has been shown to improve the problem solving power of
		 genetic programming over a range of problems. Previous
		 work has shown that it can also produce hyperselection
		 events, in which a single individual is selected many
		 more times than other individuals. Here we investigate
		 the role that hyperselection plays in the
		 problem-solving performance of lexicase selection. We
		 run genetic programming on a set of program synthesis
		 benchmark problems using lexicase and tournament
		 selection, confirming that hyperselection occurs
		 significantly more often and more drastically with
		 lexicase selection, which also performs significantly
		 better. We then show results from an experiment
		 indicating that hyperselection is not integral to the
		 problem-solving performance or diversity maintenance
		 observed when using lexicase selection. We conclude
		 that the power of lexicase selection stems from the
		 collection of individuals that it selects, not from the
		 unusual frequencies with which it sometimes selects
		 them.},
  notes = {Washington and Lee University, University of Minnesota
		 Morris, Hampshire College GECCO-2016 A Recombination of
		 the 25th International Conference on Genetic Algorithms
		 (ICGA-2016) and the 21st Annual Genetic Programming
		 Conference (GP-2016)},
  doi-url = {http://dx.doi.org/10.1145/2908812.2908851},
  note = {\textbf{Nominated, Best Paper Award, Genetic Programming Track} (39\% acceptance rate out of 31 submissions in track, 3 best paper nominations)}
}
@inproceedings{Helmuth:2015:GECCO,
  author = {Thomas Helmuth and Lee Spector},
  title = {General Program Synthesis Benchmark Suite},
  booktitle = {GECCO '15: Proceedings of the 2015 conference on Genetic and
		 Evolutionary Computation Conference},
  year = {2015},
  noeditor = {Sara Silva and Anna I Esparcia-Alcazar and Manuel
		 Lopez-Ibanez and Sanaz Mostaghim and Jon Timmis and
		 Christine Zarges and Luis Correia and Terence Soule and
		 Mario Giacobini and Ryan Urbanowicz and Youhei Akimoto
		 and Tobias Glasmachers and Francisco {Fernandez de
		 Vega} and Amy Hoover and Pedro Larranaga and Marta Soto
		 and Carlos Cotta and Francisco B. Pereira and Julia
		 Handl and Jan Koutnik and Antonio Gaspar-Cunha and
		 Heike Trautmann and Jean-Baptiste Mouret and Sebastian
		 Risi and Ernesto Costa and Oliver Schuetze and
		 Krzysztof Krawiec and Alberto Moraglio and Julian F.
		 Miller and Pawel Widera and Stefano Cagnoni and JJ
		 Merelo and Emma Hart and Leonardo Trujillo and Marouane
		 Kessentini and Gabriela Ochoa and Francisco Chicano and
		 Carola Doerr},
  isbn13 = {978-1-4503-3472-3},
  pages = {1039--1046},
  keywords = {genetic algorithms, genetic programming},
  month = {11-15 } # jul,
  organisation = {SIGEVO},
  address = {Madrid, Spain},
  url = {http://doi.acm.org/10.1145/2739480.2754769},
  doi = {doi:10.1145/2739480.2754769},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2015-GECCO-benchmark-suite.pdf},
  associated = {http://thelmuth.github.io/GECCO_2015_Benchmarks_Materials/},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {Recent interest in the development and use of
		 non-trivial benchmark problems for genetic programming
		 research has highlighted the scarcity of general
		 program synthesis (also called traditional programming)
		 benchmark problems. We present a suite of 29 general
		 program synthesis benchmark problems systematically
		 selected from sources of introductory computer science
		 programming problems. This suite is suitable for
		 experiments with any program synthesis system driven by
		 input/output examples. We present results from
		 illustrative experiments using our reference
		 implementation of the problems in the PushGP genetic
		 programming system. The results show that the problems
		 in the suite vary in difficulty and can be useful for
		 assessing the capabilities of a program synthesis
		 system.},
  notes = {Also known as \cite{2754769} GECCO-2015 A joint
		 meeting of the twenty fourth international conference
		 on genetic algorithms (ICGA-2015) and the twentith
		 annual genetic programming conference (GP-2015)},
  doi-url = {http://dx.doi.org/10.1145/2739480.2754769}
}
@inproceedings{LaCava:2015:GECCO,
  author = {William {La Cava} and Thomas Helmuth and Lee Spector
		 and Kourosh Danai},
  title = {Genetic Programming with Epigenetic Local Search},
  booktitle = {GECCO '15: Proceedings of the 2015 conference on Genetic and
		 Evolutionary Computation Conference},
  year = {2015},
  noeditor = {Sara Silva and Anna I Esparcia-Alcazar and Manuel
		 Lopez-Ibanez and Sanaz Mostaghim and Jon Timmis and
		 Christine Zarges and Luis Correia and Terence Soule and
		 Mario Giacobini and Ryan Urbanowicz and Youhei Akimoto
		 and Tobias Glasmachers and Francisco {Fernandez de
		 Vega} and Amy Hoover and Pedro Larranaga and Marta Soto
		 and Carlos Cotta and Francisco B. Pereira and Julia
		 Handl and Jan Koutnik and Antonio Gaspar-Cunha and
		 Heike Trautmann and Jean-Baptiste Mouret and Sebastian
		 Risi and Ernesto Costa and Oliver Schuetze and
		 Krzysztof Krawiec and Alberto Moraglio and Julian F.
		 Miller and Pawel Widera and Stefano Cagnoni and JJ
		 Merelo and Emma Hart and Leonardo Trujillo and Marouane
		 Kessentini and Gabriela Ochoa and Francisco Chicano and
		 Carola Doerr},
  isbn13 = {978-1-4503-3472-3},
  pages = {1055--1062},
  keywords = {genetic algorithms, genetic programming},
  month = {11-15 } # jul,
  organisation = {SIGEVO},
  address = {Madrid, Spain},
  url = {http://doi.acm.org/10.1145/2739480.2754763},
  doi = {doi:10.1145/2739480.2754763},
  pdf = {http://hampshire.edu/lspector/pubs/Epigenetics_2015_GECCO_final.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {We focus on improving genetic programming through
		 local search of the space of program structures using
		 an inheritable epigenetic layer that specifies active
		 and inactive genes. We explore several genetic
		 programming implementations that represent the
		 different properties that epigenetics can provide, such
		 as passive structure, phenotypic plasticity, and
		 inheritable gene regulation. We apply these
		 implementations to several symbolic regression and
		 program synthesis problems. For the symbolic regression
		 problems, the results indicate that epigenetic local
		 search consistently improves genetic programming by
		 producing smaller solution programs with better
		 fitness. Furthermore, we find that incorporating
		 epigenetic modification as a mutation step in program
		 synthesis problems can improve the ability of genetic
		 programming to find exact solutions. By analyzing
		 population homology we show that the epigenetic
		 implementations maintain diversity in silenced portions
		 of programs which may provide protection from premature
		 convergence.},
  notes = {Also known as \cite{2754763} GECCO-2015 A joint
		 meeting of the twenty fourth international conference
		 on genetic algorithms (ICGA-2015) and the twentith
		 annual genetic programming conference (GP-2015)},
  doi-url = {http://dx.doi.org/10.1145/2739480.2754763},
  note = {\textbf{Nominated, Best Paper Award, Genetic Programming Track} (44\% acceptance rate out of 45 submissions in track, 3 best paper nominations)}
}
@inproceedings{Helmuth:2014:GECCO,
  author = {Thomas Helmuth and Lee Spector},
  title = {Word count as a traditional programming benchmark
		 problem for genetic programming},
  booktitle = {GECCO '14: Proceedings of the 2014 conference on
		 Genetic and evolutionary computation},
  year = {2014},
  noeditor = {Christian Igel and Dirk V. Arnold and Christian Gagne
		 and Elena Popovici and Anne Auger and Jaume Bacardit
		 and Dimo Brockhoff and Stefano Cagnoni and Kalyanmoy
		 Deb and Benjamin Doerr and James Foster and Tobias
		 Glasmachers and Emma Hart and Malcolm I. Heywood and
		 Hitoshi Iba and Christian Jacob and Thomas Jansen and
		 Yaochu Jin and Marouane Kessentini and Joshua D.
		 Knowles and William B. Langdon and Pedro Larranaga and
		 Sean Luke and Gabriel Luque and John A. W. McCall and
		 Marco A. {Montes de Oca} and Alison Motsinger-Reif and
		 Yew Soon Ong and Michael Palmer and Konstantinos E.
		 Parsopoulos and Guenther Raidl and Sebastian Risi and
		 Guenther Ruhe and Tom Schaul and Thomas Schmickl and
		 Bernhard Sendhoff and Kenneth O. Stanley and Thomas
		 Stuetzle and Dirk Thierens and Julian Togelius and
		 Carsten Witt and Christine Zarges},
  isbn13 = {978-1-4503-2662-9},
  pages = {919--926},
  keywords = {genetic algorithms, genetic programming},
  month = {12-16 } # jul,
  organisation = {SIGEVO},
  address = {Vancouver, BC, Canada},
  url = {http://doi.acm.org/10.1145/2576768.2598230},
  doi = {doi:10.1145/2576768.2598230},
  pdf = {https://github.com/thelmuth/GECCO_2014_WC_Materials/raw/master/wc.pdf},
  associated = {http://thelmuth.github.io/GECCO_2014_WC_Materials/},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {The Unix utility program wc, which stands for word
		 count, takes any number of files and prints the number
		 of newlines, words, and characters in each of the
		 files. We show that genetic programming can find
		 programs that replicate the core functionality of the
		 wc utility, and propose this problem as a traditional
		 programming benchmark for genetic programming systems.
		 This wc problem features key elements of programming
		 tasks that often confront human programmers, including
		 requirements for multiple data types, a large
		 instruction set, control flow, and multiple outputs.
		 Furthermore, it mimics the behavior of a real-world
		 utility program, showing that genetic programming can
		 automatically synthesize programs with general utility.
		 We suggest statistical procedures that should be used
		 to compare performances of different systems on
		 traditional programming problems such as the wc
		 problem, and present the results of a short experiment
		 using the problem. Finally, we give a short analysis of
		 evolved solution programs, showing how they make use of
		 traditional programming concepts.},
  notes = {Also known as \cite{2598230} GECCO-2014 A joint
		 meeting of the twenty third international conference on
		 genetic algorithms (ICGA-2014) and the nineteenth
		 annual genetic programming conference (GP-2014)},
  doi-url = {http://dx.doi.org/10.1145/2576768.2598230}
}
@inproceedings{Spector:2012:GECCO,
  author = {Lee Spector and Kyle Harrington and Thomas Helmuth},
  title = {Tag-based modularity in tree-based genetic
		 programming},
  booktitle = {GECCO '12: Proceedings of the fourteenth international
		 conference on Genetic and evolutionary computation
		 conference},
  year = {2012},
  noeditor = {Terry Soule and Anne Auger and Jason Moore and David
		 Pelta and Christine Solnon and Mike Preuss and Alan
		 Dorin and Yew-Soon Ong and Christian Blum and Dario
		 Landa Silva and Frank Neumann and Tina Yu and Aniko
		 Ekart and Will Browne and Tim Kovacs and Man-Leung Wong
		 and Clara Pizzuti and Jon Rowe and Tobias Friedrich and
		 Giovanni Squillero and Nicolas Bredeche and Stephen
		 Smith and Alison Motsinger-Reif and Jose Lozano and
		 Martin Pelikan and Silja Meyer-Nienberg and Christian
		 Igel and Greg Hornby and Rene Doursat and Steve
		 Gustafson and Gustavo Olague and Shin Yoo and John
		 Clark and Gabriela Ochoa and Gisele Pappa and Fernando
		 Lobo and Daniel Tauritz and Jurgen Branke and Kalyanmoy
		 Deb},
  isbn13 = {978-1-4503-1177-9},
  pages = {815--822},
  keywords = {genetic algorithms, genetic programming},
  month = {7-11 } # jul,
  organisation = {SIGEVO},
  address = {Philadelphia, Pennsylvania, USA},
  url = {http://dl.acm.org/citation.cfm?doid=2330163.2330276},
  doi = {doi:10.1145/2330163.2330276},
  pdf = {http://hampshire.edu/lspector/pubs/p815.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {Several techniques have been developed for allowing
		 genetic programming systems to produce programs that
		 make use of subroutines, macros, and other modular
		 program structures. A recently proposed technique,
		 based on the tagging and tag-based retrieval of blocks
		 of code, has been shown to have novel and desirable
		 features, but this was demonstrated only within the
		 context of the PushGP genetic programming system.
		 Following a suggestion in the GECCO-2011 publication on
		 this technique we show here how tag-based modules can
		 be incorporated into a more standard tree-based genetic
		 programming system. We describe the technique in detail
		 along with some possible extensions, outline arguments
		 for its simplicity and potential power, and present
		 results obtained using the technique on problems for
		 which other modularization techniques have been shown
		 to be useful. The results are mixed; substantial
		 benefits are seen on the lawnmower problem but not on
		 the Boolean even-4-parity problem. We discuss the
		 observed results and directions for future research.},
  notes = {Also known as \cite{2330276} GECCO-2012 A joint
		 meeting of the twenty first international conference on
		 genetic algorithms (ICGA-2012) and the seventeenth
		 annual genetic programming conference (GP-2012)},
  doi-url = {http://dx.doi.org/10.1145/2330163.2330276}
}
@inproceedings{Spector:2011:GECCO,
  author = {Lee Spector and Brian Martin and Kyle Harrington and
		 Thomas Helmuth},
  title = {Tag-based modules in genetic programming},
  booktitle = {GECCO '11: Proceedings of the 13th annual conference
		 on Genetic and evolutionary computation},
  year = {2011},
  isbn13 = {978-1-4503-0557-0},
  pages = {1419--1426},
  keywords = {genetic algorithms, genetic programming, pushGP,
		 lawnmower},
  month = {12-16 } # jul,
  organisation = {SIGEVO},
  address = {Dublin, Ireland},
  url = {http://dl.acm.org/citation.cfm?doid=2001576.2001767},
  doi = {doi:10.1145/2001576.2001767},
  pdf = {http://hampshire.edu/lspector/pubs/spector-tags-gecco-2011-with-citation.pdf},
  associated = {http://hampshire.edu/lspector/tags-gecco-2011/},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {In this paper we present a new technique for evolving
		 modular programs with genetic programming. The
		 technique is based on the use of tags that evolving
		 programs may use to label and later to refer to code
		 fragments. Tags may refer inexactly, permitting the
		 labelling and use of code fragments to co-evolve in an
		 incremental way. The technique can be implemented as a
		 minor modification to an existing, general purpose
		 genetic programming system, and it does not require
		 pre-specification of the module architecture of evolved
		 programs. We demonstrate that tag-based modules readily
		 evolve and that this allows problem solving effort to
		 scale well with problem size. We also show that the
		 tag-based module technique is effective even in
		 complex, non-uniform problem environments for which
		 previous techniques perform poorly. We demonstrate the
		 technique in the context of the stack-based genetic
		 programming system PushGP, but we also briefly discuss
		 ways in which it may be used with other kinds of
		 genetic programming systems.},
  notes = {Section 7: tags in other forms of GP Tag data to be
		 tried. Also known as \cite{2001767} GECCO-2011 A joint
		 meeting of the twentieth international conference on
		 genetic algorithms (ICGA-2011) and the sixteenth annual
		 genetic programming conference (GP-2011)},
  doi-url = {http://dx.doi.org/10.1145/2001576.2001767}
}
@inproceedings{Ahmad:2018:GECCO,
  author = {Hammad Ahmad and Thomas Helmuth},
  title = {A comparison of semantic-based initialization methods
		 for genetic programming},
  booktitle = {GECCO '18: Proceedings of the Genetic and Evolutionary
		 Computation Conference Companion},
  year = {2018},
  noeditor = {Carlos Cotta and Tapabrata Ray and Hisao Ishibuchi and
		 Shigeru Obayashi and Bogdan Filipic and Thomas
		 Bartz-Beielstein and Grant Dick and Masaharu Munetomo
		 and Silvino {Fernandez Alzueta} and Thomas Stuetzle and
		 Pablo Valledor Pellicer and Manuel Lopez-Ibanez and
		 Daniel R. Tauritz and Pietro S. Oliveto and Thomas
		 Weise and Borys Wrobel and Ales Zamuda and Anne Auger
		 and Julien Bect and Dimo Brockhoff and Nikolaus Hansen
		 and Rodolphe {Le Riche} and Victor Picheny and Bilel
		 Derbel and Ke Li and Hui Li and Xiaodong Li and Saul
		 Zapotecas and Qingfu Zhang and Stephane Doncieux and
		 Richard Duro and Joshua Auerbach and Harold {de Vladar}
		 and Antonio J. Fernandez-Leiva and JJ Merelo and Pedro
		 A. Castillo-Valdivieso and David Camacho-Fernandez and
		 Francisco {Chavez de la O} and Ozgur Akman and Khulood
		 Alyahya and Juergen Branke and Kevin Doherty and
		 Jonathan Fieldsend and Giuseppe Carlo Marano and Nikos
		 D. Lagaros and Koichi Nakayama and Chika Oshima and
		 Stefan Wagner and Michael Affenzeller and Boris Naujoks
		 and Vanessa Volz and Tea Tusar and Pascal Kerschke and
		 Riyad Alshammari and Tokunbo Makanju and Brad Alexander
		 and Saemundur O. Haraldsson and Markus Wagner and John
		 R. Woodward and Shin Yoo and John McCall and Nayat
		 Sanchez-Pi and Luis Marti and Danilo Vasconcellos and
		 Masaya Nakata and Anthony Stein and Nadarajen Veerapen
		 and Arnaud Liefooghe and Sebastien Verel and Gabriela
		 Ochoa and Stephen L. Smith and Stefano Cagnoni and
		 Robert M. Patton and William {La Cava} and Randal Olson
		 and Patryk Orzechowski and Ryan Urbanowicz and Ivanoe
		 {De Falco} and Antonio {Della Cioppa} and Ernesto
		 Tarantino and Umberto Scafuri and P. G. M. Baltus and
		 Giovanni Iacca and Ahmed Hallawa and Anil Yaman and
		 Alma Rahat and Handing Wang and Yaochu Jin and David
		 Walker and Richard Everson and Akira Oyama and Koji
		 Shimoyama and Hemant Kumar and Kazuhisa Chiba and
		 Pramudita Satria Palar},
  isbn13 = {978-1-4503-5764-7},
  pages = {1878--1881},
  address = {Kyoto, Japan},
  doi = {doi:10.1145/3205651.3208218},
  url = {http://doi.acm.org/10.1145/3205651.3208218},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2018-GECCO-workshop-semantic-initialization.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  month = {15-19 } # jul,
  organisation = {SIGEVO},
  keywords = {genetic algorithms, genetic programming},
  abstract = {During the initialization step, a genetic programming
		 (GP) system traditionally creates a population of
		 completely random programs to populate the initial
		 population. These programs almost always perform poorly
		 in terms of their total error---some might not even
		 output the correct data type. In this paper, we present
		 new methods for initialization that attempt to generate
		 programs that are somewhat relevant to the problem
		 being solved and/or increase the initial diversity
		 (both error and behavioural diversity) of the
		 population prior to the GP run. By seeding the
		 population---and thereby eliminating worthless programs
		 and increasing the initial diversity of the
		 population---we hope to improve the performance of the
		 GP system. Here, we present two novel techniques for
		 initialization (Lexicase Seeding and Pareto Seeding)
		 and compare them to a previous method (Enforced Diverse
		 Populations) and traditional, non-seeded
		 initialization. Surprisingly, we found that none of the
		 initialization m},
  notes = {Also known as \cite{3208218} GECCO-2018 A
		 Recombination of the 27th International Conference on
		 Genetic Algorithms (ICGA-2018) and the 23rd Annual
		 Genetic Programming Conference (GP-2018)},
  doi-url = {http://dx.doi.org/10.1145/3205651.3208218}
}
@inproceedings{Pantridge:2018:GECCO,
  author = {Edward Pantridge and Thomas Helmuth and Nicholas
		 Freitag McPhee and Lee Spector},
  title = {Specialization and elitism in lexicase and tournament
		 selection},
  booktitle = {GECCO '18: Proceedings of the Genetic and Evolutionary
		 Computation Conference Companion},
  year = {2018},
  noeditor = {Carlos Cotta and Tapabrata Ray and Hisao Ishibuchi and
		 Shigeru Obayashi and Bogdan Filipic and Thomas
		 Bartz-Beielstein and Grant Dick and Masaharu Munetomo
		 and Silvino {Fernandez Alzueta} and Thomas Stuetzle and
		 Pablo Valledor Pellicer and Manuel Lopez-Ibanez and
		 Daniel R. Tauritz and Pietro S. Oliveto and Thomas
		 Weise and Borys Wrobel and Ales Zamuda and Anne Auger
		 and Julien Bect and Dimo Brockhoff and Nikolaus Hansen
		 and Rodolphe {Le Riche} and Victor Picheny and Bilel
		 Derbel and Ke Li and Hui Li and Xiaodong Li and
		 Sa{\'u}l Zapotecas and Qingfu Zhang and St{\'e}phane
		 Doncieux and Richard Duro and Joshua Auerbach and
		 Harold {de Vladar} and Antonio J. Fernandez-Leiva and
		 JJ Merelo and Pedro A. Castillo-Valdivieso and David
		 Camacho-Fernandez and Francisco {Chavez de la O} and
		 Ozgur Akman and Khulood Alyahya and Juergen Branke and
		 Kevin Doherty and Jonathan Fieldsend and Giuseppe Carlo
		 Marano and Nikos D. Lagaros and Koichi Nakayama and
		 Chika Oshima and Stefan Wagner and Michael Affenzeller
		 and Boris Naujoks and Vanessa Volz and Tea Tusar and
		 Pascal Kerschke and Riyad Alshammari and Tokunbo
		 Makanju and Brad Alexander and Saemundur O. Haraldsson
		 and Markus Wagner and John R. Woodward and Shin Yoo and
		 John McCall and Nayat Sanchez-Pi and Luis Mart{\'i} and
		 Danilo Vasconcellos and Masaya Nakata and Anthony Stein
		 and Nadarajen Veerapen and Arnaud Liefooghe and
		 S{\'e}bastien Verel and Gabriela Ochoa and Stephen L.
		 Smith and Stefano Cagnoni and Robert M. Patton and
		 William {La Cava} and Randal Olson and Patryk
		 Orzechowski and Ryan Urbanowicz and Ivanoe {De Falco}
		 and Antonio {Della Cioppa} and Ernesto Tarantino and
		 Umberto Scafuri and P. G. M. Baltus and Giovanni Iacca
		 and Ahmed Hallawa and Anil Yaman and Alma Rahat and
		 Handing Wang and Yaochu Jin and David Walker and
		 Richard Everson and Akira Oyama and Koji Shimoyama and
		 Hemant Kumar and Kazuhisa Chiba and Pramudita Satria
		 Palar},
  isbn13 = {978-1-4503-5764-7},
  pages = {1914--1917},
  address = {Kyoto, Japan},
  url = {http://doi.acm.org/10.1145/3205651.3208220},
  doi = {doi:10.1145/3205651.3208220},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2018-GECCO-workshop-lexicase-specialization.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  month = {15-19 } # jul,
  organisation = {SIGEVO},
  notes = {Also known as \cite{3208220} GECCO-2018 A
		 Recombination of the 27th International Conference on
		 Genetic Algorithms (ICGA-2018) and the 23rd Annual
		 Genetic Programming Conference (GP-2018)},
  doi-url = {http://dx.doi.org/10.1145/3205651.3208220}
}
@inproceedings{Pantridge:2017:GECCOa,
  author = {Edward Pantridge and Thomas Helmuth and Nicholas
		 Freitag McPhee and Lee Spector},
  title = {On the Difficulty of Benchmarking Inductive Program
		 Synthesis Methods},
  booktitle = {Proceedings of the Genetic and Evolutionary
		 Computation Conference Companion},
  series = {GECCO '17},
  year = {2017},
  isbn13 = {978-1-4503-4939-0},
  address = {Berlin, Germany},
  pages = {1589--1596},
  size = {8 pages},
  url = {http://doi.acm.org/10.1145/3067695.3082533},
  doi = {doi:10.1145/3067695.3082533},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2017-GECCO-workshop-benchmarking-program-synthesis.pdf},
  acmid = {3082533},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  keywords = {genetic algorithms, genetic programming, benchmarking,
		 inductive program synthesis, machine learning},
  month = {15-19 } # jul,
  abstract = {A variety of inductive program synthesis (IPS)
		 techniques have recently been developed, emerging from
		 different areas of computer science. However, these
		 techniques have not been adequately compared on general
		 program synthesis problems. In this paper we compare
		 several methods on problems requiring solution programs
		 to handle various data types, control structures, and
		 numbers of outputs. The problem set also spans levels
		 of abstraction; some would ordinarily be approached
		 using machine code or assembly language, while others
		 would ordinarily be approached using high-level
		 languages. The presented comparisons are focused on the
		 possibility of success; that is, on whether the system
		 can produce a program that passes all tests, for all
		 training and unseen testing inputs. The compared
		 systems are Flash Fill, MagicHaskeller, TerpreT, and
		 two forms of genetic programming. The two genetic
		 programming methods chosen were PushGP and Grammar
		 Guided Genetic Programming. The results suggest that
		 PushGP and, to an extent, TerpreT and Grammar Guided
		 Genetic Programming are more capable of finding
		 solutions than the others, albeit at a higher
		 computational cost. A more salient observation is the
		 difficulty of comparing these methods due to
		 drastically different intended applications, despite
		 the common goal of program synthesis.},
  notes = {Also known as
		 \cite{Pantridge:2017:DBI:3067695.3082533} GECCO-2017 A
		 Recombination of the 26th International Conference on
		 Genetic Algorithms (ICGA-2017) and the 22nd Annual
		 Genetic Programming Conference (GP-2017)},
  doi-url = {http://dx.doi.org/10.1145/3067695.3082533}
}
@inproceedings{Helmuth:2016:GECCOcomp,
  author = {Thomas Helmuth and Nicholas Freitag McPhee and Lee
		 Spector},
  title = {Effects of Lexicase and Tournament Selection on
		 Diversity Recovery and Maintenance},
  booktitle = {GECCO '16 Companion: Proceedings of the Companion
		 Publication of the 2016 Annual Conference on Genetic
		 and Evolutionary Computation},
  year = {2016},
  noeditor = {Tobias Friedrich and Frank Neumann and Andrew M.
		 Sutton and Martin Middendorf and Xiaodong Li and Emma
		 Hart and Mengjie Zhang and Youhei Akimoto and Peter A.
		 N. Bosman and Terry Soule and Risto Miikkulainen and
		 Daniele Loiacono and Julian Togelius and Manuel
		 Lopez-Ibanez and Holger Hoos and Julia Handl and
		 Faustino Gomez and Carlos M. Fonseca and Heike
		 Trautmann and Alberto Moraglio and William F. Punch and
		 Krzysztof Krawiec and Zdenek Vasicek and Thomas Jansen
		 and Jim Smith and Simone Ludwig and JJ Merelo and Boris
		 Naujoks and Enrique Alba and Gabriela Ochoa and Simon
		 Poulding and Dirk Sudholt and Timo Koetzing},
  isbn13 = {978-1-4503-4323-7},
  pages = {983--990},
  address = {Denver, Colorado, USA},
  month = {20-24 } # jul,
  keywords = {genetic algorithms, genetic programming},
  organisation = {SIGEVO},
  doi = {doi:10.1145/2908961.2931657},
  url = {http://doi.acm.org/10.1145/2908961.2931657},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GECCO-workshop-diversity-maintenance.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {In genetic programming systems, parent selection
		 algorithms select the programs from which offspring
		 will be produced by random variation and recombination.
		 While most parent selection algorithms select programs
		 on the basis of aggregate performance on multiple test
		 cases, the lexicase selection algorithm considers each
		 test case individually, in random order, for each
		 parent selection event. Prior work has shown that
		 lexicase selection can produce both more diverse
		 populations and more solutions when applied to several
		 hard problems. Here we examine the effects of lexicase
		 selection, compared to those of the more traditional
		 tournament selection algorithm, on population error
		 diversity using two program synthesis problems. We
		 conduct experiments in which the same initial
		 population is used to start multiple runs, each using a
		 different random number seed. The initial populations
		 are extracted from genetic programming runs, and fall
		 into three categories: high diversity populations, low
		 diversity populations, and populations that occur after
		 diversity crashes. The reported data shows that
		 lexicase selection can maintain high error diversity
		 and also that it can re-diversify less-diverse
		 populations, while tournament selection consistently
		 produces lower diversity.},
  notes = {Distributed at GECCO-2016.},
  doi-url = {http://dx.doi.org/10.1145/2908961.2931657}
}
@inproceedings{Spector:2016:GECCOcomp,
  author = {Lee Spector and Nicholas Freitag McPhee and Thomas
		 Helmuth and Maggie M. Casale and Julian Oks},
  title = {Evolution Evolves with Autoconstruction},
  booktitle = {GECCO '16 Companion: Proceedings of the Companion
		 Publication of the 2016 Annual Conference on Genetic
		 and Evolutionary Computation},
  year = {2016},
  noeditor = {Tobias Friedrich and Frank Neumann and Andrew M.
		 Sutton and Martin Middendorf and Xiaodong Li and Emma
		 Hart and Mengjie Zhang and Youhei Akimoto and Peter A.
		 N. Bosman and Terry Soule and Risto Miikkulainen and
		 Daniele Loiacono and Julian Togelius and Manuel
		 Lopez-Ibanez and Holger Hoos and Julia Handl and
		 Faustino Gomez and Carlos M. Fonseca and Heike
		 Trautmann and Alberto Moraglio and William F. Punch and
		 Krzysztof Krawiec and Zdenek Vasicek and Thomas Jansen
		 and Jim Smith and Simone Ludwig and JJ Merelo and Boris
		 Naujoks and Enrique Alba and Gabriela Ochoa and Simon
		 Poulding and Dirk Sudholt and Timo Koetzing},
  isbn13 = {978-1-4503-4323-7},
  pages = {1349--1356},
  address = {Denver, Colorado, USA},
  month = {20-24 } # jul,
  keywords = {genetic algorithms, genetic programming},
  organisation = {SIGEVO},
  doi = {doi:10.1145/2908961.2931727},
  url = {http://doi.acm.org/10.1145/2908961.2931727},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GECCO-workshop-autoconstruction.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {In autoconstructive evolutionary algorithms,
		 individuals implement not only candidate solutions to
		 specified computational problems, but also their own
		 methods for variation of offspring. This makes it
		 possible for the variation methods to themselves
		 evolve, which could, in principle, produce a system
		 with an enhanced capacity for adaptation and superior
		 problem solving power. Prior work on autoconsruction
		 has explored a range of system designs and their
		 evolutionary dynamics, but it has not solved hard
		 problems. Here we describe a new approach that can
		 indeed solve at least some hard problems. We present
		 the key components of this approach, including the use
		 of linear genomes for hierarchically structured
		 programs, a diversity-maintaining parent selection
		 algorithm, and the enforcement of diversification
		 constraints on offspring. We describe a software
		 synthesis benchmark problem that our new approach can
		 solve, and we present visualizations of data from
		 single successful runs of autoconstructive vs.
		 non-autoconstructive systems on this problem. While
		 anecdotal, the data suggests that variation methods,
		 and therefore significant aspects of the evolutionary
		 process, evolve over the course of the autoconstructive
		 runs.},
  notes = {Distributed at GECCO-2016.},
  doi-url = {http://dx.doi.org/10.1145/2908961.2931727}
}
@inproceedings{McPhee:2016:GECCOcomp,
  author = {Nicholas Freitag McPhee and Maggie M. Casale and
		 Mitchell Finzel and Thomas Helmuth and Lee Spector},
  title = {Visualizing Genetic Programming Ancestries},
  booktitle = {GECCO '16 Companion: Proceedings of the Companion
		 Publication of the 2016 Annual Conference on Genetic
		 and Evolutionary Computation},
  year = {2016},
  isbn13 = {978-1-4503-4323-7},
  pages = {1419--1426},
  keywords = {genetic algorithms, genetic programming, pushGP, liner
		 genetic programming, Clojush, lexicase selection},
  month = {20-24 } # jul,
  organisation = {SIGEVO},
  address = {Denver, Colorado, USA},
  doi = {doi:10.1145/2908961.2931741},
  url = {http://doi.acm.org/10.1145/2908961.2931741},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GECCO-workshop-visualizing-ancestries.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  size = {8 pages},
  abstract = {Previous work has demonstrated the utility of graph
		 databases as a tool for collecting, analysing, and
		 visualizing ancestry in evolutionary computation runs.
		 That work focused on sections of individual runs,
		 whereas this paper illustrates the application of these
		 ideas on the entirety of large runs (up to three
		 hundred thousand individuals) and combinations of
		 multiple runs. Here we use these tools to generate
		 graphs showing all the ancestors of successful
		 individuals from a variety of stack-based genetic
		 programming runs on software synthesis problems. These
		 graphs highlight important moments in the evolutionary
		 process. They also allow us to compare the dynamics for
		 successful and unsuccessful runs. As well as displaying
		 these full ancestry graphs, we use a variety of
		 standard techniques such as size, colour, pattern,
		 labelling, and opacity to visualize other important
		 information such as fitness, which genetic operators
		 were used, and the distance between parent and child
		 genomes. While this generates an extremely rich
		 visualization, the amount of data can also be somewhat
		 overwhelming, so we also explore techniques for
		 filtering these graphs that allow us to better
		 understand the key dynamics.},
  notes = {Titan graph database. Tinkerpop query tools. Graphviz
		 dot. Mutation and crossover. Hyperselection events.
		 Replace space with newline benchmark. p1420 'uses
		 restricted Boltzmann machines (RBMs) to compress the
		 200 error values into 24-bit RGB color values' p1423
		 'presence of an individual could have had..impact..even
		 if..never contributed genetic material' p1423
		 'unfilter' p1426 future dynamic tools. My pdf reader
		 barfs Slides
		 https://www.slideshare.net/NicMcPhee/visualizing-genetic-programming-ancestries
		 Cites \cite{series/sci/BurlacuAWKK15}},
  doi-url = {http://dx.doi.org/10.1145/2908961.2931741}
}
@inproceedings{Liskowski:2015:GECCOcomp,
  author = {Pawel Liskowski and Krzysztof Krawiec and Thomas
		 Helmuth and Lee Spector},
  title = {Comparison of Semantic-aware Selection Methods in
		 Genetic Programming},
  booktitle = {GECCO 2015 Semantic Methods in Genetic Programming
		 (SMGP'15) Workshop},
  year = {2015},
  noeditor = {Colin Johnson and Krzysztof Krawiec and Alberto
		 Moraglio and Michael O'Neill},
  isbn13 = {978-1-4503-3488-4},
  keywords = {genetic algorithms, genetic programming, Semantic
		 Methods in (SMGP'15) Workshop},
  pages = {1301--1307},
  month = {11-15 } # jul,
  organisation = {SIGEVO},
  address = {Madrid, Spain},
  url = {http://doi.acm.org/10.1145/2739482.2768505},
  doi = {doi:10.1145/2739482.2768505},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2015-GECCO-semantic-aware-selection.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {This study investigates the performance of several
		 semantic-aware selection methods for genetic
		 programming (GP). In particular, we consider methods
		 that do not rely on complete GP semantics (i.e., a
		 tuple of outputs produced by a program for fitness
		 cases (tests)), but on binary outcome vectors that only
		 state whether a given test has been passed by a program
		 or not. This allows us to relate to test-based problems
		 commonly considered in the domain of coevolutionary
		 algorithms and, in prospect, to address a wider range
		 of practical problems, in particular the problems where
		 desired program output is unknown (e.g., evolving GP
		 controllers). The selection methods considered in the
		 paper include implicit fitness sharing (ifs), discovery
		 of derived objectives (doc), lexicase selection (lex),
		 as well as a hybrid of the latter two. These
		 techniques, together with a few variants, are
		 experimentally compared to each other and to
		 conventional GP on a battery of discrete benchmark
		 problems. The outcomes indicate superior performance of
		 lex and ifs, with some variants of doc showing certain
		 potential.},
  notes = {Also known as \cite{2768505} Distributed at
		 GECCO-2015.},
  doi-url = {http://dx.doi.org/10.1145/2739482.2768505}
}
@inproceedings{Helmuth:2013:GECCOcomp,
  author = {Thomas Helmuth and Lee Spector},
  title = {Evolving a digital multiplier with the {PushGP} genetic
		 programming system},
  booktitle = {GECCO '13 Companion: Proceeding of the fifteenth
		 annual conference companion on Genetic and evolutionary
		 computation conference companion},
  year = {2013},
  noeditor = {Christian Blum and Enrique Alba and Thomas
		 Bartz-Beielstein and Daniele Loiacono and Francisco
		 Luna and Joern Mehnen and Gabriela Ochoa and Mike
		 Preuss and Emilia Tantar and Leonardo Vanneschi and
		 Kent McClymont and Ed Keedwell and Emma Hart and Kevin
		 Sim and Steven Gustafson and Ekaterina Vladislavleva
		 and Anne Auger and Bernd Bischl and Dimo Brockhoff and
		 Nikolaus Hansen and Olaf Mersmann and Petr Posik and
		 Heike Trautmann and Muhammad Iqbal and Kamran Shafi and
		 Ryan Urbanowicz and Stefan Wagner and Michael
		 Affenzeller and David Walker and Richard Everson and
		 Jonathan Fieldsend and Forrest Stonedahl and William
		 Rand and Stephen L. Smith and Stefano Cagnoni and
		 Robert M. Patton and Gisele L. Pappa and John Woodward
		 and Jerry Swan and Krzysztof Krawiec and
		 Alexandru-Adrian Tantar and Peter A. N. Bosman and
		 Miguel Vega-Rodriguez and Jose M. Chaves-Gonzalez and
		 David L. Gonzalez-Alvarez and Sergio Santander-Jimenez
		 and Lee Spector and Maarten Keijzer and Kenneth
		 Holladay and Tea Tusar and Boris Naujoks},
  isbn13 = {978-1-4503-1964-5},
  keywords = {genetic algorithms, genetic programming},
  pages = {1627--1634},
  month = {6-10 } # jul,
  organisation = {SIGEVO},
  address = {Amsterdam, The Netherlands},
  url = {http://dl.acm.org/citation.cfm?doid=2464576.2466814},
  doi = {doi:10.1145/2464576.2466814},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/digital-multiplier-GECCO-2013.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {A recent article on benchmark problems for genetic
		 programming suggested that researchers focus attention
		 on the digital multiplier problem, also known as the
		 multiple output multiplier problem, in part because it
		 is scalable and in part because the requirement of
		 multiple outputs presents challenges for some forms of
		 genetic programming [20]. Here we demonstrate the
		 application of stack-based genetic programming to the
		 digital multiplier problem using the PushGP genetic
		 programming system, which evolves programs expressed in
		 the stack-based Push programming language. We
		 demonstrate the use of output instructions and argue
		 that they provide a natural mechanism for producing
		 multiple outputs in a stack-based genetic programming
		 context. We also show how two recent developments in
		 PushGP dramatically improve the performance of the
		 system on the digital multiplier problem. These
		 developments are the ULTRA genetic operator, which
		 produces offspring via Uniform Linear Transformation
		 with Repair and Alternation [12], and lexicase
		 selection, which selects parents according to
		 performance on cases considered sequentially in random
		 order [11]. Our results using these techniques show not
		 only their utility, but also the utility of the digital
		 multiplier problem as a benchmark problem for genetic
		 programming research. The results also demonstrate the
		 exibility of stack-based genetic programming for
		 solving problems with multiple outputs and for serving
		 as a platform for experimentation with new genetic
		 programming techniques.},
  notes = {Also known as \cite{2466814} Distributed at
		 GECCO-2013.},
  doi-url = {http://dx.doi.org/10.1145/2464576.2466814}
}
@inproceedings{Helmuth:2011:GECCOcomp,
  author = {Thomas Helmuth and Lee Spector and Brian Martin},
  title = {Size-based tournaments for node selection},
  booktitle = {GECCO 2011 Graduate students workshop},
  year = {2011},
  noeditor = {Miguel Nicolau},
  isbn13 = {978-1-4503-0690-4},
  keywords = {genetic algorithms, genetic programming},
  pages = {799--802},
  month = {12-16 } # jul,
  organisation = {SIGEVO},
  address = {Dublin, Ireland},
  url = {http://dl.acm.org/citation.cfm?doid=2001858.2002095},
  doi = {doi:10.1145/2001858.2002095},
  pdf = {http://hampshire.edu/lspector/pubs/node-selection-gecco2011-cited.pdf},
  erratum = {http://cs.hamilton.edu/~thelmuth/node-selection-gecco-2011.html},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {In genetic programming, the reproductive operators of
		 crossover and mutation both require the selection of
		 nodes from the reproducing individuals. Both unbiased
		 random selection and Koza 90/10 mechanisms remain
		 popular, despite their arbitrary natures and a lack of
		 evidence for their effectiveness. It is generally
		 considered problematic to select from all nodes with a
		 uniform distribution, since this causes terminal nodes
		 to be selected most of the time. This can limit the
		 complexity of program fragments that can be exchanged
		 in crossover, and it may also lead to code bloat when
		 leaf nodes are replaced with larger new subtrees during
		 mutation. We present a new node selection method that
		 selects nodes based on a tournament, from which the
		 largest participating subtree is selected. We show this
		 method of size-based tournaments improves performance
		 on three standard test problems with no increases in
		 code bloat as compared to unbiased and Koza 90/10
		 selection methods.},
  notes = {Also known as \cite{2002095} Distributed on CD-ROM at
		 GECCO-2011. ACM Order Number 910112.},
  doi-url = {http://dx.doi.org/10.1145/2001858.2002095}
}
@inproceedings{Spector:2019:GPTP,
  author = {Edward Pantridge and Thomas Helmuth and Lee Spector},
  title = {Comparison of Linear Genome Representations For
		 Software Synthesis},
  booktitle = {Genetic Programming Theory and Practice XVII},
  year = {2019},
  editor = {Wolfgang Banzhaf and Erik Goodman and Leigh Sheneman
		 and Leonardo Trujillo and Bill Worzel},
  pages = {255--274},
  address = {East Lansing, MI, USA},
  month = {16-19 } # may,
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming},
  isbn13 = {978-3-030-39957-3},
  url = {https://link.springer.com/chapter/10.1007/978-3-030-39958-0_13},
  doi = {doi:10.1007/978-3-030-39958-0_13},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2019-GPTP-linear-genomes-representations.pdf},
  abstract = {In many genetic programming systems, the program
		 variation and execution processes operate on different
		 program representations. The representations on which
		 variation operates are referred to as genomes.
		 Unconstrained linear genome representations can provide
		 a variety of advantages, including reduced complexity
		 of program generation, variation, simplification and
		 serialization operations. The Plush genome
		 representation, which uses epigenetic markers on linear
		 genomes to express nonlinear structures, has supported
		 the production of state-of-the-art results in program
		 synthesis with the PushGP genetic programming system.
		 Here we present a new, simpler, non-epigenetic
		 alternative to Plush, called Plushy, that appears to
		 maintain all of the advantages of Plush while providing
		 additional benefits. These results illustrate the
		 virtues of unconstrained linear genome representations
		 more generally, and may be transferable to genetic
		 programming systems that target different languages for
		 evolved programs.},
  notes = {Part of \cite{Banzhaf:2019:GPTP}, published after the
		 workshop},
  doi-url = {http://dx.doi.org/10.1007/978-3-030-39958-0_13}
}
@inproceedings{Troise:2017:GPTP,
  author = {Sarah Anne Troise and Thomas Helmuth},
  title = {Lexicase Selection with Weighted Shuffle},
  booktitle = {Genetic Programming Theory and Practice XV},
  editor = {Wolfgang Banzhaf and Randal S. Olson and William
		 Tozier and Rick Riolo},
  year = {2017},
  series = {Genetic and Evolutionary Computation},
  pages = {89--104},
  address = {University of Michigan in Ann Arbor, USA},
  month = may # { 18--20},
  organisation = {the Center for the Study of Complex Systems},
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming},
  isbn13 = {978-3-319-90511-2},
  url = {https://link.springer.com/chapter/10.1007/978-3-319-90512-9_6},
  doi = {doi:10.1007/978-3-319-90512-9_6},
  abstract = {Semantic-aware methods in genetic programming take
		 into account information about programs performances
		 across a set of test cases. Lexicase parent selection,
		 a semantic-aware selection, randomly shuffles the list
		 of test cases and places more emphasis on those test
		 cases that randomly appear earlier in the ordering than
		 those that appear later in the ordering. In this work,
		 we explore methods for weighting this shuffling of test
		 cases to give some test cases more influence over
		 selection than others. We design and test a variety of
		 weighted shuffle algorithms and methods for weighting
		 test cases. In experiments on two program synthesis
		 benchmark problems, we find that none of these methods
		 significantly outperform regular lexicase selection. We
		 analyse these results by examining how each method
		 affects population diversity, and find that those
		 methods that perform much worse also have significantly
		 lower diversity.},
  notes = {GPTP 2017, Part of \cite{Banzhaf:2017:GPTP} published
		 after the workshop in 2018},
  doi-url = {http://dx.doi.org/10.1007/978-3-319-90512-9_6},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2017-GPTP-weighted-lexicase.pdf}
}
@inproceedings{Spector:2017:GPTP,
  author = {Lee Spector and William {La Cava} and Saul Shanabrook
		 and Thomas Helmuth and Edward Pantridge},
  title = {Relaxations of Lexicase Parent Selection},
  booktitle = {Genetic Programming Theory and Practice XV},
  editor = {Wolfgang Banzhaf and Randal S. Olson and William
		 Tozier and Rick Riolo},
  year = {2017},
  series = {Genetic and Evolutionary Computation},
  pages = {105--120},
  address = {University of Michigan in Ann Arbor, USA},
  month = may # { 18--20},
  organisation = {the Center for the Study of Complex Systems},
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming},
  isbn13 = {978-3-319-90511-2},
  url = {https://link.springer.com/chapter/10.1007/978-3-319-90512-9_7},
  doi = {doi:10.1007/978-3-319-90512-9_7},
  abstract = {In a genetic programming system, the parent selection
		 algorithm determines which programs in the evolving
		 population will be used as the material out of which
		 new programs will be constructed. The lexicase parent
		 selection algorithm chooses a parent by considering all
		 test cases, individually, one at a time, in a random
		 order, to reduce the pool of possible parent programs.
		 Lexicase selection is ordinarily strict, in that a
		 program can only be selected if it has the best error
		 in the entire population on the first test case
		 considered, and the best error relative to all other
		 programs that remain in the pool each time it is
		 reduced. This strictness may exclude high-quality
		 candidates from consideration for parenthood, and hence
		 from exploration by the evolutionary process. In this
		 chapter we describe and present results of four
		 variants of lexicase selection that relax these strict
		 constraints: epsilon lexicase selection, random
		 threshold lexicase selection, MADCAP epsilon lexicase
		 selection, and truncated lexicase selection. We present
		 the results of experiments with genetic programming
		 systems using these and other parent selection
		 algorithms on symbolic regression and software
		 synthesis problems. We also briefly discuss the
		 relations between lexicase selection and work on
		 many-objective optimization, and the implications of
		 these considerations for future work on parent
		 selection in genetic programming.},
  notes = {GPTP 2017, Part of \cite{Banzhaf:2017:GPTP} published
		 after the workshop in 2018},
  doi-url = {http://dx.doi.org/10.1007/978-3-319-90512-9_7},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2017-GPTP-relaxed-lexicase.pdf}
}
@inproceedings{Helmuth:2016:GPTP,
  author = {Thomas Helmuth and Lee Spector and Nicholas Freitag
		 McPhee and Saul Shanabrook},
  title = {Linear Genomes for Structured Programs},
  booktitle = {Genetic Programming Theory and Practice XIV},
  year = {2016},
  editor = {Rick Riolo and Bill Worzel and Brian Goldman and Bill
		 Tozier},
  pages = {85--100},
  address = {Ann Arbor, USA},
  month = {19-21 } # may,
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming, Uniform
		 variation, linear genomes, Push, Plush},
  isbn13 = {978-3-319-97087-5},
  url = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GPTP-plush.pdf},
  url = {https://www.springer.com/us/book/9783319970875},
  doi = {doi:10.1007/978-3-319-97088-2_6},
  size = {15 pages},
  abstract = {In most genetic programming systems, candidate
		 solution programs themselves serve as the genetic
		 material upon which variation operators act. However,
		 because of the hierarchical structure of computer
		 programs, and the syntactic constraints that they must
		 obey, it is difficult to implement variation operators
		 that affect different parts of programs with uniform
		 probability. This can have detrimental effects on
		 evolutionary search. In prior work, structured programs
		 were linearised prior to variation in order to
		 facilitate uniformity, but this necessitated syntactic
		 repair after variation, which reintroduced
		 non-uniformities. In this chapter we describe a new
		 approach that uses linear genomes, from which
		 structured programs are expressed only for the purpose
		 of fitness testing. We present the new approach in
		 detail and show how it facilitates both uniform
		 variation and the evolution of programs with meaningful
		 structure.},
  notes = {Part of \cite{Tozier:2016:GPTP} published after the
		 workshop},
  doi-url = {http://dx.doi.org/10.1007/978-3-319-97088-2_6},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GPTP-plush.pdf}
}
@inproceedings{McPhee:2016:GPTP,
  author = {Nicholas Freitag McPhee and Mitchell D. Finzel and
		 Maggie M. Casale and Thomas Helmuth and Lee Spector},
  title = {A detailed analysis of a {PushGP} run},
  booktitle = {Genetic Programming Theory and Practice XIV},
  year = {2016},
  editor = {Rick Riolo and Bill Worzel and Brian Goldman and Bill
		 Tozier},
  pages = {65--83},
  address = {Ann Arbor, USA},
  month = {19-21 } # may,
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming, PushGP,
		 ancestry graph, lineage, inheritance},
  isbn13 = {978-3-319-97087-5},
  url = {https://www.springer.com/us/book/9783319970875},
  doi = {doi:10.1007/978-3-319-97088-2_5},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2016-GPTP-full-run-analysis.pdf},
  abstract = {In evolutionary computation runs there is a great deal
		 of data that could be saved and analysed. This data is
		 often put aside, however, in favour of focusing on the
		 final outcomes, typically captured and presented in the
		 form of summary statistics and performance plots. Here
		 we examine a genetic programming run in detail and
		 trace back from the solution to determine how it was
		 derived. To visualize this genetic programming run, the
		 ancestry graph is extracted, running from the
		 solution(s) in the final generation up to their
		 ancestors in the initial random population. The key
		 instructions in the solution are also identified, and a
		 genetic ancestry graph is constructed, a subgraph of
		 the ancestry graph containing only those individuals
		 contributed genetic information (or instructions) to
		 the solution. This visualization and our ability to
		 trace these key instructions throughout the run allowed
		 us to identify general inheritance patterns and key
		 evolutionary moments in this run.},
  notes = {Part of \cite{Tozier:2016:GPTP} published after the
		 workshop},
  doi-url = {http://dx.doi.org/10.1007/978-3-319-97088-2_5}
}
@inproceedings{Helmuth:2015:GPTP,
  author = {Thomas Helmuth and Nicholas Freitag McPhee and Lee
		 Spector},
  title = {Lexicase Selection For Program Synthesis: {A}
		 Diversity Analysis},
  booktitle = {Genetic Programming Theory and Practice XIII},
  year = {2015},
  noeditor = {Rick Riolo and William P. Worzel and M. Kotanchek and
		 A. Kordon},
  series = {Genetic and Evolutionary Computation},
  address = {Ann Arbor, USA},
  month = may,
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming, Lexicase
		 selection, diversity, tournament selection, implicit
		 fitness sharing},
  isbn13 = {978-3-319-34223-8},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2015-GPTP-lexicase-diversity-analysis.pdf},
  url = {http://www.springer.com/us/book/9783319342214},
  size = {16 pages},
  abstract = {Lexicase selection is a selection method for
		 evolutionary computation in which individuals are
		 selected by filtering the population according to
		 performance on test cases, considered in random order.
		 When used as the parent selection method in genetic
		 programming, lexicase selection has been shown to
		 provide significant improvements in problem-solving
		 power. In this chapter we investigate the reasons for
		 the success of lexicase selection, focusing on measures
		 of population diversity. We present data from eight
		 program synthesis problems and compare lexicase
		 selection to tournament selection and selection based
		 on implicit fitness sharing. We conclude that lexicase
		 selection does indeed produce more diverse populations,
		 which helps to explain the utility of lexicase
		 selection for program synthesis.},
  notes = {Replace Space With Newline, Syllables, String Lengths
		 Backwards, Negative To Zero, Double Letters, Scrabble
		 Score, Checksum, Count Odds.
		 http://cscs.umich.edu/gptp-workshops/ Part of
		 \cite{Riolo:2015:GPTP} Published after the workshop in
		 2016}
}
@inproceedings{McPhee:2015:GPTP,
  author = {Nicholas Freitag McPhee and David Donatucci and Thomas
		 Helmuth},
  title = {Using Graph Databases to Explore Genetic Programming
		 Run Dynamics},
  booktitle = {Genetic Programming Theory and Practice XIII},
  year = {2015},
  noeditor = {Rick Riolo and William P. Worzel and M. Kotanchek and
		 A. Kordon},
  series = {Genetic and Evolutionary Computation},
  address = {Ann Arbor, USA},
  month = may,
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming},
  isbn13 = {978-3-319-34223-8},
  url = {http://www.springer.com/us/book/9783319342214},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2015-GPTP-graph-database.pdf},
  notes = {http://cscs.umich.edu/gptp-workshops/ Part of
		 \cite{Riolo:2015:GPTP} Published after the workshop in
		 2016}
}
@inproceedings{Kannappan:2014:GPTP,
  author = {Karthik Kannappan and Lee Spector and Moshe Sipper and
		 Thomas Helmuth and William La Cava and Jake Wisdom and
		 Omri Bernstein},
  title = {Analyzing a Decade of Human-Competitive (``{HUMIE}'')
		 Winners: What Can We Learn?},
  booktitle = {Genetic Programming Theory and Practice XII},
  year = {2014},
  noeditor = {Rick Riolo and William P. Worzel and Mark Kotanchek},
  series = {Genetic and Evolutionary Computation},
  pages = {149--166},
  address = {Ann Arbor, USA},
  month = {8-10 } # may,
  publisher = {Springer},
  keywords = {genetic algorithms, genetic programming, HUMIES,
		 Evolutionary Computation, Human Competitive},
  isbn13 = {978-3-319-16029-0},
  url = {http://link.springer.com/chapter/10.1007%2F978-3-319-16030-6_9},
  doi = {doi:10.1007/978-3-319-16030-6_9},
  pdf = {http://faculty.hampshire.edu/lspector/pubs/Anaylzing_the_Humies.pdf},
  size = {16 pages},
  abstract = {Techniques in evolutionary computation (EC) have
		 improved significantly over the years, leading to a
		 substantial increase in the complexity of problems that
		 can be solved by EC-based approaches. The HUMIES awards
		 at the Genetic and Evolutionary Computation Conference
		 are designed to recognise work that has not just solved
		 some problem via techniques from evolutionary
		 computation, but has produced a solution that is
		 demonstrably human-competitive. In this chapter, we
		 take a look across the winners of the past 10 years of
		 the HUMIES awards, and analyse them to determine
		 whether there are specific approaches that consistently
		 show up in the HUMIE winners. We believe that this
		 analysis may lead to interesting insights regarding
		 prospects and strategies for producing further human
		 competitive results.},
  notes = {http://cscs.umich.edu/gptp-workshops/ Part of
		 \cite{Riolo:2014:GPTP} published after the workshop in
		 2015},
  doi-url = {http://dx.doi.org/10.1007/978-3-319-16030-6_9}
}
@incollection{Spector:2013:GPTP,
  author = {Lee Spector and Thomas Helmuth},
  title = {Uniform Linear Transformation with Repair and
		 Alternation in Genetic Programming},
  booktitle = {Genetic Programming Theory and Practice XI},
  year = {2013},
  series = {Genetic and Evolutionary Computation},
  noeditor = {Rick Riolo and Jason H. Moore and Mark Kotanchek},
  publisher = {Springer},
  chapter = {8},
  pages = {137--153},
  address = {Ann Arbor, USA},
  month = {9-11 } # may,
  keywords = {genetic algorithms, genetic programming, Uniform
		 mutation, Uniform crossover, ULTRA, Push, PushGP, Drug
		 bioavailability problem, Pagie-1 problem, Factorial
		 regression, Boolean multiplexer problem},
  isbn13 = {978-1-4939-0374-0},
  url = {http://link.springer.com/chapter/10.1007%2F978-1-4939-0375-7_8},
  doi = {doi:10.1007/978-1-4939-0375-7_8},
  pdf = {http://faculty.hampshire.edu/lspector/pubs/spector-gptp-2013-preprint-erratum.pdf},
  abstract = {Several genetic programming researchers have argued
		 for the utility of genetic operators that act
		 uniformly. By act uniformly we mean two specific
		 things: that the probability of an inherited program
		 component being modified during inheritance is
		 independent of the size and shape of the parent
		 programs beyond the component in question; and that
		 pairs of parents are combined in ways that allow
		 arbitrary combinations of components from each parent
		 to appear in the child. Uniform operators described in
		 previous work have had limited utility, however,
		 because of a mismatch between the relevant notions of
		 uniformity and the hierarchical structure and variable
		 sizes of many genetic programming representations. In
		 this chapter we describe a new genetic operator, ULTRA,
		 which incorporates aspects of both mutation and
		 crossover and acts approximately uniformly across
		 programs of variable sizes and structures. ULTRA treats
		 hierarchical programs as linear sequences and includes
		 a repair step to ensure that syntax constraints are
		 satisfied after variation. We show that on the drug
		 bioavailability and Pagie-1 benchmark problems ULTRA
		 produces significant improvements both in
		 problem-solving power and in program size relative to
		 standard operators. Experiments with factorial
		 regression and with the Boolean 6-multiplexer problem
		 demonstrate that ULTRA can manipulate programs that
		 make use of hierarchical structure, but also that it is
		 not always beneficial. The demonstrations evolve
		 programs in the Push programming language, which makes
		 repair particularly simple, but versions of the
		 technique should be applicable in other genetic
		 programming systems as well.},
  notes = {http://cscs.umich.edu/gptp-workshops/ Part of
		 \cite{Riolo:2013:GPTP} published after the workshop in
		 2013},
  doi-url = {http://dx.doi.org/10.1007/978-1-4939-0375-7_8}
}
@incollection{Helmuth:2012:GPTP,
  author = {Thomas Helmuth and Lee Spector},
  title = {Evolving {SQL} Queries from Examples with
		 Developmental Genetic Programming},
  booktitle = {Genetic Programming Theory and Practice X},
  year = {2012},
  series = {Genetic and Evolutionary Computation},
  noeditor = {Rick Riolo and Ekaterina Vladislavleva and Marylyn D.
		 Ritchie and Jason H. Moore},
  publisher = {Springer},
  chapter = {1},
  pages = {1--14},
  address = {Ann Arbor, USA},
  month = {12-14 } # may,
  keywords = {genetic algorithms, genetic programming, Data mining,
		 Classification, SQL, Push, PushGP},
  isbn13 = {978-1-4614-6845-5},
  url = {http://link.springer.com/chapter/10.1007%2F978-1-4614-6846-2_1},
  doi = {doi:10.1007/978-1-4614-6846-2_1},
  pdf = {http://hampshire.edu/lspector/pubs/gptp-2012-preprint.pdf},
  abstract = {Large databases are becoming ever more ubiquitous, as
		 are the opportunities for discovering useful knowledge
		 within them. Evolutionary computation methods such as
		 genetic programming have previously been applied to
		 several aspects of the problem of discovering knowledge
		 in databases. The more specific task of producing
		 human-comprehensible SQL queries has several potential
		 applications but has thus far been explored only to a
		 limited extent. In this chapter we show how
		 developmental genetic programming can automatically
		 generate SQL queries from sets of positive and negative
		 examples. We show that a developmental genetic
		 programming system can produce queries that are
		 reasonably accurate while excelling in human
		 comprehensibility relative to the well-known C5.0
		 decision tree generation system.},
  notes = {part of \cite{Riolo:2012:GPTP} published after the
		 workshop in 2013},
  doi-url = {http://dx.doi.org/10.1007/978-1-4614-6846-2_1}
}
@incollection{Spector:2011:GPTP,
  author = {Lee Spector and Kyle Harrington and Brian Martin and
		 Thomas Helmuth},
  title = {What's in an Evolved Name? The Evolution of Modularity
		 via Tag-Based Reference},
  booktitle = {Genetic Programming Theory and Practice IX},
  year = {2011},
  noeditor = {Rick Riolo and Ekaterina Vladislavleva and Jason H.
		 Moore},
  series = {Genetic and Evolutionary Computation},
  address = {Ann Arbor, USA},
  month = {12-14 } # may,
  publisher = {Springer},
  chapter = {1},
  pages = {1--16},
  keywords = {genetic algorithms, genetic programming, modularity,
		 names, tags, stack-based genetic programming, Push
		 programming language, PushGP},
  isbn13 = {978-1-4614-1769-9},
  url = {http://link.springer.com/chapter/10.1007%2F978-1-4614-1770-5_1},
  pdf = {http://hampshire.edu/lspector/pubs/spector-gptp11-preprint.pdf},
  doi = {doi:10.1007/978-1-4614-1770-5_1},
  size = {18 pages},
  abstract = {Programming languages provide a variety of mechanisms
		 to associate names with values, and these mechanisms
		 play a central role in programming practice. For
		 example, they allow multiple references to the same
		 storage location or function in different parts of a
		 complex program. By contrast, the representations used
		 in current genetic programming systems provide few if
		 any naming mechanisms, and it is therefore generally
		 not possible for evolved programs to use names in
		 sophisticated ways. we describe a new approach to names
		 in genetic programming that is based on John Holland's
		 concept of tags. We demonstrate the use of tag-based
		 names, we describe some of the ways in which they may
		 help to extend the power and reach of genetic
		 programming systems and we look at the ways that
		 tag-based names are actually used in an evolved program
		 that solves a robot navigation problem.},
  notes = {section 1. 'Grammars of most programming languages
		 fail to be fully context free because name definitions
		 and uses must match...' Push in C++, Java, JavaScript,
		 Python, Common Lips, Clojure, Scheme, Erlang and R.
		 Tags both for values (variables) and code (functions).
		 untag. scoping rules? dirt-sensing robot 15 modules
		 (table 1-1). See also \cite{Spector:2011:GECCO}. Part
		 of \cite{Riolo:2011:GPTP}},
  affiliation = {Cognitive Science, Hampshire College, Amherst, MA
		 01002, USA},
  doi-url = {http://dx.doi.org/10.1007/978-1-4614-1770-5_1}
}
@inproceedings{Helmuth:2020:GECCOcomp,
  author = {Thomas Helmuth and Amr Abdelhady},
  title = {Benchmarking Parent Selection for Program Synthesis by
		 Genetic Programming},
  year = {2020},
  noeditor = {Richard Allmendinger and Hugo Terashima Marin and
		 Efren Mezura Montes and Thomas Bartz-Beielstein and
		 Bogdan Filipic and Ke Tang and David Howard and Emma
		 Hart and Gusz Eiben and Tome Eftimov and William {La
		 Cava} and Boris Naujoks and Pietro Oliveto and Vanessa
		 Volz and Thomas Weise and Bilel Derbel and Ke Li and
		 Xiaodong Li and Saul Zapotecas and Qingfu Zhang and Rui
		 Wang and Ran Cheng and Guohua Wu and Miqing Li and
		 Hisao Ishibuchi and Jonathan Fieldsend and Ozgur Akman
		 and Khulood Alyahya and Juergen Branke and John R.
		 Woodward and Daniel R. Tauritz and Marco Baioletti and
		 Josu Ceberio Uribe and John McCall and Alfredo Milani
		 and Stefan Wagner and Michael Affenzeller and Bradley
		 Alexander and Alexander (Sandy) Brownlee and Saemundur
		 O. Haraldsson and Markus Wagner and Nayat Sanchez-Pi
		 and Luis Marti and Silvino {Fernandez Alzueta} and
		 Pablo {Valledor Pellicer} and Thomas Stuetzle and
		 Matthew Johns and Nick Ross and Ed Keedwell and Herman
		 Mahmoud and David Walker and Anthony Stein and Masaya
		 Nakata and David Paetzel and Neil Vaughan and Stephen
		 Smith and Stefano Cagnoni and Robert M. Patton and
		 Ivanoe {De Falco} and Antonio {Della Cioppa} and
		 Umberto Scafuri and Ernesto Tarantino and Akira Oyama
		 and Koji Shimoyama and Hemant Kumar Singh and Kazuhisa
		 Chiba and Pramudita Satria Palar and Alma Rahat and
		 Richard Everson and Handing Wang and Yaochu Jin and
		 Erik Hemberg and Riyad Alshammari and Tokunbo Makanju
		 and Fuijimino-shi and Ivan Zelinka and Swagatam Das and
		 Ponnuthurai Nagaratnam and Roman Senkerik},
  isbn13 = {9781450371278},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  url = {https://doi.org/10.1145/3377929.3389987},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2020-GECCO-poster-benchmarking-parent-selection.pdf},
  doi = {doi:10.1145/3377929.3389987},
  booktitle = {Proceedings of the 2020 Genetic and Evolutionary
		 Computation Conference Companion},
  pages = {237--238},
  size = {2 pages},
  keywords = {genetic algorithms, genetic programming, parent
		 selection, benchmark, program synthesis},
  series = {GECCO '20},
  month = jul # { 8-12},
  organisation = {SIGEVO},
  notes = {Also known as \cite{10.1145/3377929.3389987}
		 GECCO-2020 A Recombination of the 29th International
		 Conference on Genetic Algorithms (ICGA) and the 25th
		 Annual Genetic Programming Conference (GP)},
  doi-url = {http://dx.doi.org/10.1145/3377929.3389987}
}
@inproceedings{Helmuth:2020:GECCOcompa,
  author = {Thomas Helmuth and Lee Spector and Edward Pantridge},
  title = {Counterexample-Driven Genetic Programming without
		 Formal Specifications},
  year = {2020},
  noeditor = {Richard Allmendinger and Hugo Terashima Marin and
		 Efren Mezura Montes and Thomas Bartz-Beielstein and
		 Bogdan Filipic and Ke Tang and David Howard and Emma
		 Hart and Gusz Eiben and Tome Eftimov and William {La
		 Cava} and Boris Naujoks and Pietro Oliveto and Vanessa
		 Volz and Thomas Weise and Bilel Derbel and Ke Li and
		 Xiaodong Li and Saul Zapotecas and Qingfu Zhang and Rui
		 Wang and Ran Cheng and Guohua Wu and Miqing Li and
		 Hisao Ishibuchi and Jonathan Fieldsend and Ozgur Akman
		 and Khulood Alyahya and Juergen Branke and John R.
		 Woodward and Daniel R. Tauritz and Marco Baioletti and
		 Josu Ceberio Uribe and John McCall and Alfredo Milani
		 and Stefan Wagner and Michael Affenzeller and Bradley
		 Alexander and Alexander (Sandy) Brownlee and Saemundur
		 O. Haraldsson and Markus Wagner and Nayat Sanchez-Pi
		 and Luis Marti and Silvino {Fernandez Alzueta} and
		 Pablo {Valledor Pellicer} and Thomas Stuetzle and
		 Matthew Johns and Nick Ross and Ed Keedwell and Herman
		 Mahmoud and David Walker and Anthony Stein and Masaya
		 Nakata and David Paetzel and Neil Vaughan and Stephen
		 Smith and Stefano Cagnoni and Robert M. Patton and
		 Ivanoe {De Falco} and Antonio {Della Cioppa} and
		 Umberto Scafuri and Ernesto Tarantino and Akira Oyama
		 and Koji Shimoyama and Hemant Kumar Singh and Kazuhisa
		 Chiba and Pramudita Satria Palar and Alma Rahat and
		 Richard Everson and Handing Wang and Yaochu Jin and
		 Erik Hemberg and Riyad Alshammari and Tokunbo Makanju
		 and Fuijimino-shi and Ivan Zelinka and Swagatam Das and
		 Ponnuthurai Nagaratnam and Roman Senkerik},
  isbn13 = {9781450371278},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  url = {https://doi.org/10.1145/3377929.3389983},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2020-GECCO-poster-counterexample-gp.pdf},
  doi = {doi:10.1145/3377929.3389983},
  booktitle = {Proceedings of the 2020 Genetic and Evolutionary
		 Computation Conference Companion},
  pages = {239--240},
  size = {2 pages},
  keywords = {genetic algorithms, genetic programming,
		 counterexamples, program synthesis},
  series = {GECCO '20},
  month = jul # { 8-12},
  organisation = {SIGEVO},
  notes = {Also known as \cite{10.1145/3377929.3389983}
		 GECCO-2020 A Recombination of the 29th International
		 Conference on Genetic Algorithms (ICGA) and the 25th
		 Annual Genetic Programming Conference (GP)},
  doi-url = {http://dx.doi.org/10.1145/3377929.3389983}
}
@inproceedings{Helmuth:2020:GECCOcompb,
  author = {Thomas Helmuth and Edward Pantridge and Grace Woolson
		 and Lee Spector},
  title = {Transfer Learning of Genetic Programming Instruction
		 Sets},
  year = {2020},
  noeditor = {Richard Allmendinger and Hugo Terashima Marin and
		 Efren Mezura Montes and Thomas Bartz-Beielstein and
		 Bogdan Filipic and Ke Tang and David Howard and Emma
		 Hart and Gusz Eiben and Tome Eftimov and William {La
		 Cava} and Boris Naujoks and Pietro Oliveto and Vanessa
		 Volz and Thomas Weise and Bilel Derbel and Ke Li and
		 Xiaodong Li and Saul Zapotecas and Qingfu Zhang and Rui
		 Wang and Ran Cheng and Guohua Wu and Miqing Li and
		 Hisao Ishibuchi and Jonathan Fieldsend and Ozgur Akman
		 and Khulood Alyahya and Juergen Branke and John R.
		 Woodward and Daniel R. Tauritz and Marco Baioletti and
		 Josu Ceberio Uribe and John McCall and Alfredo Milani
		 and Stefan Wagner and Michael Affenzeller and Bradley
		 Alexander and Alexander (Sandy) Brownlee and Saemundur
		 O. Haraldsson and Markus Wagner and Nayat Sanchez-Pi
		 and Luis Marti and Silvino {Fernandez Alzueta} and
		 Pablo {Valledor Pellicer} and Thomas Stuetzle and
		 Matthew Johns and Nick Ross and Ed Keedwell and Herman
		 Mahmoud and David Walker and Anthony Stein and Masaya
		 Nakata and David Paetzel and Neil Vaughan and Stephen
		 Smith and Stefano Cagnoni and Robert M. Patton and
		 Ivanoe {De Falco} and Antonio {Della Cioppa} and
		 Umberto Scafuri and Ernesto Tarantino and Akira Oyama
		 and Koji Shimoyama and Hemant Kumar Singh and Kazuhisa
		 Chiba and Pramudita Satria Palar and Alma Rahat and
		 Richard Everson and Handing Wang and Yaochu Jin and
		 Erik Hemberg and Riyad Alshammari and Tokunbo Makanju
		 and Fuijimino-shi and Ivan Zelinka and Swagatam Das and
		 Ponnuthurai Nagaratnam and Roman Senkerik},
  isbn13 = {9781450371278},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  url = {https://doi.org/10.1145/3377929.3389988},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2020-GECCO-poster-transfer-learning-instruction-sets.pdf},
  doi = {doi:10.1145/3377929.3389988},
  booktitle = {Proceedings of the 2020 Genetic and Evolutionary
		 Computation Conference Companion},
  pages = {241--242},
  size = {2 pages},
  keywords = {genetic algorithms, genetic programming, transfer
		 learning, instruction set, PushGP},
  series = {GECCO '20},
  month = jul # { 8-12},
  organisation = {SIGEVO},
  notes = {Also known as \cite{10.1145/3377929.3389988}
		 GECCO-2020 A Recombination of the 29th International
		 Conference on Genetic Algorithms (ICGA) and the 25th
		 Annual Genetic Programming Conference (GP)},
  doi-url = {http://dx.doi.org/10.1145/3377929.3389988}
}
@inproceedings{McPhee:2017:GECCOa,
  author = {Nicholas Freitag McPhee and Thomas Helmuth and Lee
		 Spector},
  title = {Using Algorithm Configuration Tools to Optimize
		 Genetic Programming Parameters: A Case Study},
  booktitle = {Proceedings of the Genetic and Evolutionary
		 Computation Conference Companion},
  series = {GECCO '17},
  year = {2017},
  isbn13 = {978-1-4503-4939-0},
  address = {Berlin, Germany},
  pages = {243--244},
  size = {2 pages},
  url = {http://doi.acm.org/10.1145/3067695.3076097},
  doi = {doi:10.1145/3067695.3076097},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2017-GECCO-poster-SMAC-and-PushGP.pdf},
  acmid = {3076097},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  keywords = {genetic algorithms, genetic programming, SMAC,
		 parameter optimization, pushGP, software synthesis},
  month = {15-19 } # jul,
  abstract = {We use Sequential Model-based Algorithm Configuration
		 (SMAC) to optimize a group of parameters for PushGP, a
		 stack-based genetic programming system, for several
		 software synthesis problems. Applying SMAC to one
		 particular problem leads to marked improvements in the
		 success rate and the speed with which a solution was
		 found for that problem. Applying these {"}tuned{"}
		 parameters to four additional problems, however, only
		 improved performance on one, and substantially reduced
		 performance on another. This suggests that SMAC is
		 overfitting, tuning the parameters in ways that are
		 highly problem specific, and raises doubts about the
		 value of using these {"}tuned{"} parameters on
		 previously unsolved problems. Efforts to use SMAC to
		 optimize PushGP parameters on other problems have been
		 less successful due to a combination of long PushGP run
		 times and low success rates, which make it hard for
		 SMAC to acquire enough information in a reasonable
		 amount of time.},
  notes = {Also known as \cite{McPhee:2017:UAC:3067695.3076097}
		 GECCO-2017 A Recombination of the 26th International
		 Conference on Genetic Algorithms (ICGA-2017) and the
		 22nd Annual Genetic Programming Conference (GP-2017)},
  doi-url = {http://dx.doi.org/10.1145/3067695.3076097}
}
@inproceedings{McPhee:2017:GECCO,
  author = {Nicholas Freitag McPhee and Maggie M. Casale and
		 Mitchell Finzel and Thomas Helmuth and Lee Spector},
  title = {Visualizing Genetic Programming Ancestries Using Graph
		 Databases},
  booktitle = {Proceedings of the Genetic and Evolutionary
		 Computation Conference Companion},
  series = {GECCO '17},
  year = {2017},
  isbn13 = {978-1-4503-4939-0},
  address = {Berlin, Germany},
  pages = {245--246},
  size = {2 pages},
  url = {http://doi.acm.org/10.1145/3067695.3075617},
  doi = {doi:10.1145/3067695.3075617},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/2017-GECCO-poster-ancestries.pdf},
  acmid = {3075617},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  keywords = {genetic algorithms, genetic programming, ancestry,
		 graph database, visualization},
  month = {15-19 } # jul,
  notes = {Also known as \cite{McPhee:2017:VGP:3067695.3075617}
		 GECCO-2017 A Recombination of the 26th International
		 Conference on Genetic Algorithms (ICGA-2017) and the
		 22nd Annual Genetic Programming Conference (GP-2017)},
  doi-url = {http://dx.doi.org/10.1145/3067695.3075617}
}
@inproceedings{Spector:2014:GECCOcomp,
  author = {Lee Spector and Thomas Helmuth},
  title = {Effective simplification of evolved push programs
		 using a simple, stochastic hill-climber},
  booktitle = {GECCO Comp '14: Proceedings of the 2014 conference
		 companion on Genetic and evolutionary computation
		 companion},
  year = {2014},
  noeditor = {Christian Igel and Dirk V. Arnold and Christian Gagne
		 and Elena Popovici and Anne Auger and Jaume Bacardit
		 and Dimo Brockhoff and Stefano Cagnoni and Kalyanmoy
		 Deb and Benjamin Doerr and James Foster and Tobias
		 Glasmachers and Emma Hart and Malcolm I. Heywood and
		 Hitoshi Iba and Christian Jacob and Thomas Jansen and
		 Yaochu Jin and Marouane Kessentini and Joshua D.
		 Knowles and William B. Langdon and Pedro Larranaga and
		 Sean Luke and Gabriel Luque and John A. W. McCall and
		 Marco A. {Montes de Oca} and Alison Motsinger-Reif and
		 Yew Soon Ong and Michael Palmer and Konstantinos E.
		 Parsopoulos and Guenther Raidl and Sebastian Risi and
		 Guenther Ruhe and Tom Schaul and Thomas Schmickl and
		 Bernhard Sendhoff and Kenneth O. Stanley and Thomas
		 Stuetzle and Dirk Thierens and Julian Togelius and
		 Carsten Witt and Christine Zarges},
  isbn13 = {978-1-4503-2881-4},
  keywords = {genetic algorithms, genetic programming: Poster},
  pages = {147--148},
  month = {12-16 } # jul,
  organisation = {SIGEVO},
  address = {Vancouver, BC, Canada},
  url = {http://doi.acm.org/10.1145/2598394.2598414},
  doi = {doi:10.1145/2598394.2598414},
  pdf = {http://cs.hamilton.edu/~thelmuth/Pubs/simplification-GECCO-2014.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {Genetic programming systems often produce programs
		 that include unnecessary code. This is undesirable for
		 several reasons, including the burdens that
		 overly-large programs put on end-users for program
		 interpretation and maintenance. The problem is
		 exacerbated by recently developed techniques, such as
		 genetic programming with geometric semantic crossover,
		 that tend to produce enormous programs. Methods for
		 automatically simplifying evolved programs are
		 therefore of interest, but automatic simplification is
		 non-trivial in the context of traditional program
		 representations with unconstrained function sets. Here
		 we show how evolved programs expressed in the
		 stack-based Push programming language can be
		 automatically and reliably simplified using a simple,
		 stochastic hill-climber. We demonstrate and
		 quantitatively characterise this simplification process
		 on programs evolved to solve four non-trivial genetic
		 programming problems with qualitatively different
		 function sets.},
  notes = {Also known as \cite{2598414} Distributed at
		 GECCO-2014.},
  doi-url = {http://dx.doi.org/10.1145/2598394.2598414}
}
@inproceedings{Helmuth:2012:GECCOcomp,
  author = {Thomas Helmuth and Lee Spector},
  title = {Empirical investigation of size-based tournaments for
		 node selection in genetic programming},
  booktitle = {GECCO Companion '12: Proceedings of the fourteenth
		 international conference on Genetic and evolutionary
		 computation conference companion},
  year = {2012},
  noeditor = {Terry Soule and Anne Auger and Jason Moore and David
		 Pelta and Christine Solnon and Mike Preuss and Alan
		 Dorin and Yew-Soon Ong and Christian Blum and Dario
		 Landa Silva and Frank Neumann and Tina Yu and Aniko
		 Ekart and Will Browne and Tim Kovacs and Man-Leung Wong
		 and Clara Pizzuti and Jon Rowe and Tobias Friedrich and
		 Giovanni Squillero and Nicolas Bredeche and Stephen
		 Smith and Alison Motsinger-Reif and Jose Lozano and
		 Martin Pelikan and Silja Meyer-Nienberg and Christian
		 Igel and Greg Hornby and Rene Doursat and Steve
		 Gustafson and Gustavo Olague and Shin Yoo and John
		 Clark and Gabriela Ochoa and Gisele Pappa and Fernando
		 Lobo and Daniel Tauritz and Jurgen Branke and Kalyanmoy
		 Deb},
  isbn13 = {978-1-4503-1178-6},
  keywords = {genetic algorithms, Genetic programming: Poster},
  pages = {1485--1486},
  month = {7-11 } # jul,
  organisation = {SIGEVO},
  address = {Philadelphia, Pennsylvania, USA},
  url = {http://dl.acm.org/citation.cfm?doid=2330784.2331004},
  doi = {doi:10.1145/2330784.2331004},
  pdf = {http://hampshire.edu/lspector/pubs/p1485.pdf},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  abstract = {In genetic programming systems, genetic operators must
		 select nodes upon which to act; the method by which
		 they select nodes influences problem solving
		 performance and possibly also code growth. A recently
		 proposed node selection method using size-based
		 tournaments has been shown to have potential, but
		 variations of the method have not been studied
		 systematically. Here we extend the ideas of size-based
		 tournaments and test how they can improve
		 problem-solving performance. We consider allowing
		 tournament size to depend on whether we are selecting
		 nodes within donors for crossover, recipients for
		 crossover, or targets of mutation. We also consider
		 tournaments that bias selection toward smaller trees
		 rather than larger trees. We find that differentiating
		 between donors and recipients is probably not
		 worthwhile and that size 2 tournaments perform
		 near-optimally.},
  notes = {Also known as \cite{2331004} Distributed at
		 GECCO-2012. ACM Order Number 910122.},
  doi-url = {http://dx.doi.org/10.1145/2330784.2331004}
}
@inproceedings{Spector:2011:FSE:2001858.2001932,
  author = {Spector, Lee and Helmuth, Thomas and Harrington, Kyle},
  title = {Fecundity and Selectivity in Evolutionary Computation},
  booktitle = {Proceedings of the 13th Annual Conference Companion on Genetic and Evolutionary Computation},
  series = {GECCO '11},
  year = {2011},
  isbn = {978-1-4503-0690-4},
  location = {Dublin, Ireland},
  pages = {129--130},
  numpages = {2},
  url = {http://doi.acm.org/10.1145/2001858.2001932},
  doi = {10.1145/2001858.2001932},
  pdf = {http://hampshire.edu/lspector/pubs/decimation-gecco2011-cited.pdf},
  acmid = {2001932},
  month = {12-16 } # jul,
  organisation = {SIGEVO},
  address = {Dublin, Ireland},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  keywords = {deb's deceptive problem, decimation, fecundity, selection, truncation}
}
@inproceedings{Helmuth:2021:GECCOtutorial:lexicase,
  author = {Thomas Helmuth and Bill La Cava},
  title = {Lexicase Selection},
  year = {2021},
  publisher = {ACM},
  publisher_address = {New York, NY, USA},
  url = {},
  pdf = {},
  doi = {},
  booktitle = {Proceedings of the 2021 Genetic and Evolutionary
		 Computation Conference Companion},
  series = {GECCO '21},
  month = jul # { 10-14},
  organisation = {SIGEVO}
}
@phdthesis{Helmuth:thesis,
  author = {Thomas Helmuth},
  title = {General Program Synthesis from Examples Using Genetic
		 Programming with Parent Selection Based on Random
		 Lexicographic Orderings of Test Cases},
  school = {College of Information and Computer Sciences,
		 University of Massachusetts Amherst},
  year = {2015},
  address = {USA},
  month = sep,
  keywords = {genetic algorithms, genetic programming, lexicase},
  url = {https://web.cs.umass.edu/publication/details.php?id=2398},
  pdf = {https://web.cs.umass.edu/publication/docs/2015/UM-CS-PhD-2015-005.pdf},
  size = {159 pages},
  abstract = {Software developers routinely create tests before
		 writing code, to ensure that their programs fulfill
		 their requirements. Instead of having human programmers
		 write the code to meet these tests, automatic program
		 synthesis systems can create programs to meet
		 specifications without human intervention, only
		 requiring examples of desired behavior. In the
		 long-term, we envision using genetic programming to
		 synthesize large pieces of software. This dissertation
		 takes steps toward this goal by investigating the
		 ability of genetic programming to solve introductory
		 computer science programming problems. We present a
		 suite of 29 benchmark problems intended to test general
		 program synthesis systems, which we systematically
		 selected from sources of introductory computer science
		 programming problems. This suite is suitable for
		 experiments with any program synthesis system driven by
		 input/output examples. Unlike existing benchmarks that
		 concentrate on constrained problem domains such as list
		 manipulation, symbolic regression, or Boolean
		 functions, this suite contains general programming
		 problems that require a range of programming
		 constructs, such as multiple data types and data
		 structures, control flow statements, and I/O. The
		 problems encompass a range of difficulties and
		 requirements as necessary to thoroughly assess the
		 capabilities of a program synthesis system. Besides
		 describing the specifications for each problem, we make
		 recommendations for experimental protocols and
		 statistical methods to use with the problems. This
		 dissertation's second contribution is an investigation
		 of behaviour-based parent selection in genetic
		 programming, concentrating on a new method called
		 lexicase selection. Most parent selection techniques
		 aggregate errors from test cases to compute a single
		 scalar fitness value; lexicase selection instead treats
		 test cases separately, never comparing error values of
		 different test cases. This property allows it to select
		 parents that specialise on some test cases even if they
		 perform poorly on others. We compare lexicase selection
		 to other parent selection techniques on our benchmark
		 suite, showing better performance for lexicase
		 selection. After observing that lexicase selection
		 increases exploration of the search space while also
		 increasing exploitation of promising programs, we
		 conduct a range of experiments to identify which
		 characteristics of lexicase selection influence its
		 utility.},
  notes = {UM-CS-Phd-2015-005 Supervised by Lee Spector GP
		 discussion list 27 Sep 2015:
		 https://groups.yahoo.com/neo/groups/genetic_programming/conversations/messages/6785}
}
@techreport{Helmuth:2015006:UM,
  author = {Thomas Helmuth and Lee Spector},
  title = {Detailed Problem Descriptions for General Program Synthesis Benchmark Suite},
  institution = {Computer Science, University of Massachusetts, Amherst},
  year = {2015},
  type = {Technical Report},
  number = {UM-CS-2015-006},
  month = {June},
  keywords = {program synthesis, genetic programming, benchmarks},
  url = {https://web.cs.umass.edu/publication/details.php?id=2387},
  pdf = {https://web.cs.umass.edu/publication/docs/2015/UM-CS-2015-006.pdf},
  size = {17 pages},
  abstract = {Recent interest in the development and use of non-trivial benchmark problems for genetic programming research has highlighted the scarcity of general program synthesis (also called ``traditional programming'') benchmark problems. We present a suite of $29$ general program synthesis benchmark problems systematically selected from sources of introductory computer science programming problems. This suite is suitable for experiments with any program synthesis system driven by input/output examples. We present results from illustrative experiments using our reference implementation of the problems in the PushGP genetic programming system. This technical report provides sufficient detail of the problems and our reference implementation for researchers to implement and attempt to solve these problems in other synthesis systems. The results show that the problems in the suite vary in difficulty and can be useful for assessing the capabilities of a program synthesis system.}
}

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