471 research outputs found
Benchmarking a Genetic Algorithm with Configurable Crossover Probability
We investigate a family of Genetic Algorithms (GAs) which
creates offspring either from mutation or by recombining two randomly chosen
parents. By scaling the crossover probability, we can thus interpolate from a
fully mutation-only algorithm towards a fully crossover-based GA. We analyze,
by empirical means, how the performance depends on the interplay of population
size and the crossover probability.
Our comparison on 25 pseudo-Boolean optimization problems reveals an
advantage of crossover-based configurations on several easy optimization tasks,
whereas the picture for more complex optimization problems is rather mixed.
Moreover, we observe that the ``fast'' mutation scheme with its are power-law
distributed mutation strengths outperforms standard bit mutation on complex
optimization tasks when it is combined with crossover, but performs worse in
the absence of crossover.
We then take a closer look at the surprisingly good performance of the
crossover-based GAs on the well-known LeadingOnes benchmark
problem. We observe that the optimal crossover probability increases with
increasing population size . At the same time, it decreases with
increasing problem dimension, indicating that the advantages of the crossover
are not visible in the asymptotic view classically applied in runtime analysis.
We therefore argue that a mathematical investigation for fixed dimensions might
help us observe effects which are not visible when focusing exclusively on
asymptotic performance bounds
Leveraging Benchmarking Data for Informed One-Shot Dynamic Algorithm Selection
A key challenge in the application of evolutionary algorithms in practice is
the selection of an algorithm instance that best suits the problem at hand.
What complicates this decision further is that different algorithms may be best
suited for different stages of the optimization process. Dynamic algorithm
selection and configuration are therefore well-researched topics in
evolutionary computation. However, while hyper-heuristics and parameter control
studies typically assume a setting in which the algorithm needs to be chosen
while running the algorithms, without prior information, AutoML approaches such
as hyper-parameter tuning and automated algorithm configuration assume the
possibility of evaluating different configurations before making a final
recommendation. In practice, however, we are often in a middle-ground between
these two settings, where we need to decide on the algorithm instance before
the run ("oneshot" setting), but where we have (possibly lots of) data
available on which we can base an informed decision.
We analyze in this work how such prior performance data can be used to infer
informed dynamic algorithm selection schemes for the solution of pseudo-Boolean
optimization problems. Our specific use-case considers a family of genetic
algorithms.Comment: Submitted for review to GECCO'2
Automated Configuration of Genetic Algorithms by Tuning for Anytime Performance
Finding the best configuration of algorithms' hyperparameters for a given
optimization problem is an important task in evolutionary computation. We
compare in this work the results of four different hyperparameter tuning
approaches for a family of genetic algorithms on 25 diverse pseudo-Boolean
optimization problems. More precisely, we compare previously obtained results
from a grid search with those obtained from three automated configuration
techniques: iterated racing, mixed-integer parallel efficient global
optimization, and mixed-integer evolutionary strategies.
Using two different cost metrics, expected running time and the area under
the empirical cumulative distribution function curve, we find that in several
cases the best configurations with respect to expected running time are
obtained when using the area under the empirical cumulative distribution
function curve as the cost metric during the configuration process. Our results
suggest that even when interested in expected running time performance, it
might be preferable to use anytime performance measures for the configuration
task. We also observe that tuning for expected running time is much more
sensitive with respect to the budget that is allocated to the target
algorithms
Iterative Schedule Optimization for Parallelization in the Polyhedron Model
In high-performance computing, one primary objective is to exploit the performance that the given target hardware can deliver to the fullest. Compilers that have the ability to automatically optimize programs for a specific target hardware can be highly useful in this context. Iterative (or search-based) compilation requires little or no prior knowledge and can adapt more easily to concrete programs and target hardware than static cost models and heuristics. Thereby, iterative compilation helps in situations in which static heuristics do not reflect the combination of input program and target hardware well. Moreover, iterative compilation may enable the derivation of more accurate cost models and heuristics for optimizing compilers. In this context, the polyhedron model is of help as it provides not only a mathematical representation of programs but, more importantly, a uniform representation of complex sequences of program transformations by schedule functions. The latter facilitates the systematic exploration of the set of legal transformations of a given program.
Early approaches to purely iterative schedule optimization in the polyhedron model do not limit their search to schedules that preserve program semantics and, thereby, suffer from the need to explore numbers of illegal schedules. More recent research ensures the legality of program transformations but presumes a sequential rather than a parallel execution of the transformed program. Other approaches do not perform a purely iterative optimization.
We propose an approach to iterative schedule optimization for parallelization and tiling in the polyhedron model. Our approach targets loop programs that profit from data locality optimization and coarse-grained loop parallelization. The schedule search space can be explored either randomly or by means of a genetic algorithm.
To determine a schedule's profitability, we rely primarily on measuring the transformed code's execution time. While benchmarking is accurate, it increases the time and resource consumption of program optimization tremendously and can even make it impractical. We address this limitation by proposing to learn surrogate models from schedules generated and evaluated in previous runs of the iterative optimization and to replace benchmarking by performance prediction to the extent possible.
Our evaluation on the PolyBench 4.1 benchmark set reveals that, in a given setting, iterative schedule optimization yields significantly higher speedups in the execution of the program to be optimized. Surrogate performance models learned from training data that was generated during previous iterative optimizations can reduce the benchmarking effort without strongly impairing the optimization result. A prerequisite for this approach is a sufficient similarity between the training programs and the program to be optimized
Using Automated Algorithm Configuration for Parameter Control
Dynamic Algorithm Configuration (DAC) tackles the question of how to
automatically learn policies to control parameters of algorithms in a
data-driven fashion. This question has received considerable attention from the
evolutionary community in recent years. Having a good benchmark collection to
gain structural understanding on the effectiveness and limitations of different
solution methods for DAC is therefore strongly desirable. Following recent work
on proposing DAC benchmarks with well-understood theoretical properties and
ground truth information, in this work, we suggest as a new DAC benchmark the
controlling of the key parameter in the
~Genetic Algorithm for solving OneMax problems. We
conduct a study on how to solve the DAC problem via the use of (static)
automated algorithm configuration on the benchmark, and propose techniques to
significantly improve the performance of the approach. Our approach is able to
consistently outperform the default parameter control policy of the benchmark
derived from previous theoretical work on sufficiently large problem sizes. We
also present new findings on the landscape of the parameter-control search
policies and propose methods to compute stronger baselines for the benchmark
via numerical approximations of the true optimal policies.Comment: To appear in the Proc. of the ACM/SIGEVO Conference on Foundations of
Genetic Algorithms (FOGA XVII
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