BranchAndXSolver

BranchAndXSolver implements the Solver interface for a Relaxation-Agnostic Branch-and-X (RABaX) Solver within the SMS++ framework: a generic enumerative solver where "X" stands for Bound / Cut / Price. It is built on top of two abstract Solver concepts that live in the SMS++ core (Change.h / ChangeSolver.h):

• ChangeSolver, a :Solver that can apply() a Change to the Block it is attached to, and the undo Change that apply() returns, so that the same Solver object can be efficiently moved between the nodes of an enumeration tree;

• RelaxationSolver, a :ChangeSolver solving a relaxation of the problem: besides the relaxation value (a valid dual bound) it can produce true solutions of the original problem (valid primal bounds), branch() to generate the children of the current node, and separate() valid cuts.

The module provides BranchAndXSolver, the enumerative :Solver itself: depth-first, breadth-first or best-first exploration, cut separation, reoptimization of the enumeration tree, parallel exploration, and an inner Solver provided either directly or through a BlockSolverConfig. See the class documentation for the full list of algorithmic parameters.

GroupChange, the Change grouping the per-node branching Changes, lives in the SMS++ core together with the ChangeSolver / RelaxationSolver concepts.

Getting started

These instructions will let you build the BranchAndXSolver module on your system.

Requirements

• The SMS++ core library and its requirements.

Build and install with CMake

Configure and build the library with:

mkdir build
cd build
cmake ..
cmake --build .

The library has the same configuration options of SMS++. When built from the SMS++ umbrella project, enable it with -DBUILD_BranchAndXSolver=ON.

Optionally, install the library in the system with:

cmake --install .

Usage with CMake

After the library is built, you can use it in your CMake project with:

find_package(BranchAndXSolver)
target_link_libraries(<my_target> SMS++::BranchAndXSolver)

Build and install with makefiles

Carefully hand-crafted makefiles have also been developed for those unwilling to use CMake. Makefiles build the executable in-source (in the same directory tree where the code is) as opposed to out-of-source (in the copy of the directory tree constructed in the build/ folder) and therefore it is more convenient when having to recompile often, such as when developing/debugging a new module, as opposed to the compile-and-forget usage envisioned by CMake.

Each executable using BranchAndXSolver has to include a "main makefile" of the module, which typically is either makefile-c including all necessary libraries comprised the "core SMS++" one, or makefile-s including all necessary libraries but not the "core SMS++" one (for the common case in which this is used together with other modules that already include them). The makefiles in turn recursively include all the required other makefiles, hence one should only need to edit the "main makefile" for compilation type (C++ compiler and its options) and it all should be good to go. In case some of the external libraries are not at their default location, it should only be necessary to create the ../extlib/makefile-paths out of the extlib/makefile-default-paths-* for your OS * and edit the relevant bits (commenting out all the rest).

Check the SMS++ installation wiki for further details.

Getting help

If you need support, you want to submit bugs or propose a new feature, you can open a new issue.

Contributing

Please read CONTRIBUTING.md for details on our code of conduct, and the process for submitting merge requests to us.

Authors

Current Lead Authors

• Antonio Frangioni
  Dipartimento di Informatica
  Università di Pisa

• Filippo Magi
  Dipartimento di Informatica
  Università di Pisa

• Donato Meoli
  Dipartimento di Informatica
  Università di Pisa

Contributors

License

This code is provided free of charge under the GNU Lesser General Public License version 3.0 - see the LICENSE file for details.

Disclaimer

The code is currently provided free of charge under an open-source license. As such, it is provided "as is", without any explicit or implicit warranty that it will properly behave or it will suit your needs. The Authors of the code cannot be considered liable, either directly or indirectly, for any damage or loss that anybody could suffer for having used it. More details about the non-warranty attached to this code are available in the license description file.