Min-Cost-Flow-Class

ReadMe for the MCFClass project, a set of C++ solvers for (Linear or Convex Quadratic Separable) Min Cost Flow Problem solvers under the same interface deriving from the base class MCFClass.

The aim of MCFClass is to provide an abstraction layer between practitioners who need to solve MCF problems within complex applications and developers of MCF software. The idea is to provide an interface which caters for all the needs that a practitioner can have, thereby allowing him/her to use whichever algorithm - among those that have an implementation conforming to this interface - without bothering with the details of the implementation, and to easily switch between different algorithms.

MCFClass defines and "exports" the types of "flows" (MCFClass::FNumber), "costs" (MCFClass::CNumber) and so on, together with a set of comparison operators (ETZ, GTZ, ...) which automatically detect whether or not the underlying types are integers or floats, inserting appropriate "epsilons" in the latter case and avoiding them (for speed) in the former; these things are sorted out at compile time without user intervention.

This release comprises:

• docs/: HTML doxygen documentation, also available at

  https://frangio68.github.io/Min-Cost-Flow-Class/

• doxygen/: files to produce the documentation

• License.md: the text of the "GNU Lesser General Public License", Version 3.0, under which most of this code is distributed (but not all of it, see RelaxIV below)

• MCFClass/: definition of the base class

• MCFClone/: implements a "fake" MCF solver that takes two "real" ones and does everything on both; useful for testing the solvers (either for correctness or for efficiency) when used within "complex" approaches

• MCFCplex/: implements a MCF solver conforming to the MCFClass interface based on calls to the commercial (but free for academic purposes) IBM/ILOG Cplex solver

• MCFSimplex/: implements a MCF solver conforming to the MCFClass interface based on the primal and dual revised network simplex algorithm

• OPTUtils/: contains the OPTUtils.h file with a few minor utility functions

• ReadMe.md: this file

• RelaxIV/: implements a MCF solver conforming to the MCFClass interface based on the RELAXIV code by D. Bertsekas and P. Tseng, as described in

  Bertsekas, Dimitri P., and Paul Tseng.
  "RELAX-IV: A faster version of the RELAX code for solving minimum
  cost flow problems." (1994), Report LIDS-P-2276, MIT
  

  be aware that RelaxIV is distributed under a less permissive academic license, which only applies to researchers of noncommercial and academic institutions, e.g., universities; if the license does not apply to you, you must not download the source or delete it immediately

• req/: folder containing two request forms for two other solvers derived from the MCFClass interface that cannot be directly distributed in the repo due to licensing restrictions, see below

• SPTree/: implements a MCF solver partly conforming to the MCFClass interface, in the sense that is only able to solve MCF instances that are in fact Shortest Path Tree ones (that is, only one source node and no arc capacities), but then does so using SPT algorithms (both label-setting and label-correcting variants can be used) that are much faster than complete MCF ones

• pyMCFSimplex-0.9/: a Python-Wrapper for the MCFSimplex solver by Johannes from the G#.Blog, check README.txt for details

• test/: contains two example Main files to use the library. One solves a given MCF instance with any one MCF solver, which can be chosen by just changing two lines of code. The other compares the results of two solvers in order to verify that they agree. See the comments in both files for more details

There are two more complete solvers available under the MCFClass interface, namely CS2 and MCFZIB. These are, however, distributed under a more restrictive academic license, which has to be explicitly accepted before getting hold of the code. Request forms are available in the req/ folder.

Build and install

You can either use CMake or plain makefiles to build the library, your choice. CMake compiles off-source and it is therefore perhaps better suited to one-off, compile-and-forget installations, whereby the provided makefiles compile on-source and we find that they are better suited while developing and testing the code (if that's your cup of tea; it is ours).

In both cases, all external dependencies should be automatically dealt with if they are installed in their default paths, as specified in the *_ROOT values of extlib/makefile-default-paths. If not, the suggested way to change them is to copy the file into extlib/makefile-paths and edit it. The file (if present) is automatically read and the values found there replace the corresponding non-default definitions. The rationale for not changing makefile-default-paths is that makefile-paths file is .gitignore-d. Hence, it should not be necessary to re-change the makefiles (or stash/restore the changes) each time the project is pulled, or manually ignore the changes when it is pushed, which is very convenient for anyone who actually develops MCFClass components (anyone there?). However, note that the reading of both extlib/makefile-default-paths and extlib/makefile-paths can be disabled; see the MCFClass_READ_PATHS option in the CMake section and the MCFC_NO_PATHS macro in the makefile section below.

Using CMake

Configure and build the library with:

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

If CPLEX is not available or you are not interested in MCFCplex, run

cmake -DMCFClass_USE_CPLEX=OFF ..

• Optionally, you can install the library with:

cmake --install .

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

find_package(MCFClass)
target_link_libraries(<my_target> MCFClass::MCFClass)

• If you use the MCFClass project inside some other project that already properly defines the *_ROOT values, you can avoid them being read by setting the option MCFClass_READ_PATHS to OFF, e.g., by adding

set(MCFClass_READ_PATHS OFF CACHE BOOL
        "Whether MCFClass will read locations for dependencies or not." FORCE)

in your CMake project.

Using makefiles

• To create the library, go into lib/ and type

make -f makefile-lib

• To test the library, go into test and type make.

• If you want to use the MCFCplex class, which comes excluded by default, uncomment the two lines in lib/makefile:

MCFCxDIR = $(libMCFClDIR)/MCFCplex
include $(MCFCxDIR)/makefile

You can similarly enable (or disable) any solver, both the LGPL ones and those under the academic license, if you have obtained them, by commenting out (or commenting) the corresponding two lines in lib/makefile.

• If you want to use MCFClass as a part of some larger project you can just include lib/makefile-c or lib/makefile-inc in the "main" makefile, provided that you have properly defined all the necessary input macros; see, e.g., test/makefile for an example.

• If you use the MCFClass project inside some other project that already properly defines the *_ROOT values, you can avoid them being read by defining the macro MCFC_NO_PATHS in your "main" makefiles prior to including lib/makefile-c or lib/makefile-inc

Other stuff

More information about (some of) the implemented algorithms can be found at

http://pages.di.unipi.it/frangio/abstracts.html#JOC06

A further solver, MCFIntPnt (based on Interior-Point algorithms) has been developed, but it has not yet reached a sufficient maturuty to be distributed; its principles are discussed at

http://pages.di.unipi.it/frangio/abstracts.html#SIOPT04 http://pages.di.unipi.it/frangio/abstracts.html#COAP06 http://pages.di.unipi.it/frangio/abstracts.html#OMS06