pymhlib  a toolbox for metaheuristics and hybrid optimization methods
Project description
pymhlib
 A Toolbox for Metaheuristics and Hybrid Optimization Methods
This project is still in early development, any feedback is much appreciated!
pymhlib
is a collection of modules supporting the efficient implementation of metaheuristics
and certain hybrid optimization approaches for solving primarily combinatorial optimization
problems in Python 3.7+.
This Python mhlib
version emerged from the
C++ mhlib
to which it has certain similarities
but also many differences.
Note that there also exists a more recent efficient Juliaimplementation of this libraries, following a similar design concept: Julia MHLib.jl
The main purpose of the library is to support rapid prototyping and teaching. While ultimately efficient implementations of such algorithms in compiled languages like Julia or C++ will in general be much faster, an advantage of the Python implementation lies in the possibly quicker development cycle.
pymhlib
is developed primarily by the
Algorithms and Complexity Group of TU Wien,
Vienna, Austria, since 2019.
Contributors:
 Günther Raidl (primarily responsible)
 Nikolaus Frohner
 Thomas Jatschka
 Daniel Obszelka
 Andreas Windbichler
Installation
Major versions of pymhlib
can be installed from PyPI
via
python3 m pip install U pymhlib
and development versions are available at https://github.com/actuwien/pymhlib.
Major Components
 solution.py:
An abstract base class
Solution
that represents a candidate solution to an optimization problem and derived classesVectorSolution
,BinaryVectorSolution
, andSetSolution
for solutions which are represented bei general fixedlength vectors, boolean vectors or sets of arbitrary elements.  binvec_solution.py:
A more specific solution class
BinaryVectorSolution
for problems in which solutions are represented by fixedlength binary vectors.  subsetvec_solution.py:
A more specific solution class
SubsetVectorSolution
for problems in which solutions are subsets of a larger set. The set is realized by an efficient numpy array which is split into two parts, the one with the included elements in sorted order and the one with the remaining elements.  permutation_solution.py:
A more specific solution class
PermutationSolution
for problems in which solutions are permutations of a set of elements.  scheduler.py: A an abstract framework for single metaheuristics that rely on iteratively applying certain methods to a current solution. Modules like gvns.py and alns.py extend this abstract class towards more specific metaheuristics.
 gvns.py: A framework for local search, iterated local search, (general) variable neighborhood search, GRASP, etc.
 alns.py: A framework for adaptive large neighborhood search (ALNS).
 par_alns.py: A multiprocess implementation of the ALNS where destroy+repair operations are parallelized.
 population.py A population class for populationbased metaheuristics.
 pbig.py: A population based iterated greedy (PBIG) algorithm.
 ssga.py: A steadystate genetic algorithm (SSGA).
 sa.py: A simulated annealing (SA) algorithm with geometric cooling.
 decision_diag.py: A generic class for (relaxed) decision diagrams for combinatorial optimization.
 log.py:
Provides two logger objects, one for writing out general log information, which is typically
written into a
*.out
file, and one for iterationwise information, which is typically written into a*.log
file. The latter is buffered in order to work also efficiently, e.g., on network drives and massive detailed log information. A classLogLevel
is provided for indented writing of log information according to a current level, which might be used for hierarchically embedded components of a larger optimization framework, such as a local search that is embedded in a populationbased approach.  settings.py:
Allows for defining modulespecific parameters directly in each module in an independent distributed
way, while values for these parameters can be provided as program arguments or in
configuration files. Most
pymhlib
modules rely on this mechanism for their external parameters.
Modules/scripts for analyzing results of many runs:

multi_run_summary.py: Collects essential information from multiple
pymhlib
algorithm runs found in the respective out and log files and returns a corresponding pandas dataframe if used as a module or as a plain ASCII table when used as independent script. The module can be easily configured to extract also arbitrary applicationspecific data. 
aggregate_results.py: Calculate grouped basic statistics for one or two dataframes/TSV files obtained e.g. from
multirunsummary.py
. In particular, two test series with different algorithms or different settings can be statistically compared, including Wilcoxon signed rank tests. The module can be used as standalone script as well as module called, e.g., from a jupyter notebook.
Demos
For demonstration purposes, simple metaheuristic approaches are provided in the demo
subdirectory for the following
wellknown combinatorial optimization problems. They can be started by
python3 m pymhlib.demos.<problem> ...
where <problem>
is one of the following and ...
represents further parameters that can be seen by providing
the option h
.
It is recommended to take such a demo as template
for solving your own problem.
maxsat
: maximum satisfiability problem based onBinaryVectorSolution
tsp
: traveling salesperson problem based onPermutationSolution
qap
: quadratic assignment problem based onPermutationSolution
vertex_cover
: minimum vertex cover problem based onSetSolution
graph_coloring
: graph coloring problem based onVectorSolution
misp
: maximum (weighted) independent set problem based onSubsetVectorSolution
mkp
: multidimensional 01 knapsack problem based onSubsetVectorSolution
Shared code of these demos is found in the submodules pymhlib.demos.common
and pymhlib.demos.graphs
,
test instance data in pymhlib.demos.data
.
Moreover, juliamaxsat.py
and juliamaxsat.jl
demonstrate the integration with the Julia programming language.
Implementing timecritical parts of an application in Julia may accelerate the code substantially.
To run this demo, Julia must be set up correctly and Python's julia
package must be installed.
While this demo derives a whole solution class in Julia, juliamaxsat2.py
is a variant where only two functions
are realized in Julia.
Changelog
Major changes in releases:
Version 0.1.4
 cleaning according to pylint warnings
 settings.parse_args may now be called multiple times
Version 0.1.3
 bug fix in 2opt neighborhood search of permutation representation
Version 0.1.2
 directory renamed to pymhlib to correspond to module name
 bug fix in Metropolis criterion of ALNS
 boolean arguments must now be specified in the command line as any other parameter
Version 0.1.1
 basic functionality test
tests/test_all.py
for all problems and algorithms added  polishing, minor fixes
Version 0.1.0
 ALNS and parallel ALNS added
 graph coloring, TSP, and minimum vertex cover demos added
 population based iterated greedy and steady state genetic algorithms added
 SA with geometric cooling added
 demos.graphs introduced
 mhlib renamed to pymhlib
 demo for interfacing with Julia added
 many smaller improvements, bug fixes, improvements in documentation
Version 0.0.1
 Initial version
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