sage-numerical-backends-coin: COIN-OR mixed integer linear programming backend for SageMath

CoinBackend has previously been available as part of the SageMath source tree, from which it is built as an "optional extension" when the cbc Sage package is installed.

However, it is not available in binary distributions such as:

• the Sage binary distribution (which does not package any optional packages),
• homebrew (which just uses the Sage binary distribution),
• Ubuntu (bionic 18.04LTS and several newer versions ship versions of SageMath, with various optional packages including CBC, but not the optional extension module CoinBackend),
• conda-forge (which ships SageMath and CBC but not the optional extension).
• Fedora

The present standalone Python package sage-numerical-backends-coin has been created from the SageMath sources, version 9.0.beta10. It can be installed on top of various Sage installations using pip, including all of the above, including older versions of Sage such as 8.1 (as shipped by Ubuntu bionic 18.04LTS).

Sage ticket https://trac.sagemath.org/ticket/28175 uses this package to remove the in-tree version of CoinBackend.

Installation

CBC can either be installed using its Sage package using

$ sage -i cbc

or any of the methods explained at https://github.com/coin-or/Cbc .

This package finds the CBC installation by means of pkgconfig.

Install this package from PyPI using

$ sage -python -m pip install sage-numerical-backends-coin

or from GitHub using

$ sage -python -m pip install git+https://github.com/mkoeppe/sage-numerical-backends-coin

(See .github/workflows/build.yml for details about package prerequisites on various systems.)

Using this package

To obtain a solver (backend) instance:

sage: from sage_numerical_backends_coin.coin_backend import CoinBackend
sage: CoinBackend()
<sage_numerical_backends_coin.coin_backend.CoinBackend object at 0x7fb72c2c7528>

Equivalently:

sage: from sage_numerical_backends_coin.coin_backend import CoinBackend
sage: from sage.numerical.backends.generic_backend import get_solver
sage: get_solver(solver=CoinBackend)
<sage_numerical_backends_coin.coin_backend.CoinBackend object at 0x7fe21ffbe2b8>

To use this solver (backend) with MixedIntegerLinearProgram:

sage: from sage_numerical_backends_coin.coin_backend import CoinBackend
sage: M = MixedIntegerLinearProgram(solver=CoinBackend)
sage: M.get_backend()
<sage_numerical_backends_coin.coin_backend.CoinBackend object at 0x7fb72c2c7868>

To make it available as the solver named 'Coin', we need to make the new module known as sage.numerical.backends.coin_backend (note dots, not underscores), using the following commands:

sage: import sage_numerical_backends_coin.coin_backend as coin_backend, sage.numerical.backends as backends, sys
sage: sys.modules['sage.numerical.backends.coin_backend'] = backends.coin_backend = coin_backend

If these commands are executed in a Sage session before any MixedIntegerLinearProgram is created, then the new 'Coin' solver wins over the 'GLPK' solver in the selection of the default MIP backend. To select the 'Coin' solver explicitly as the default MIP backend, additionally use the following command.

sage: default_mip_solver('Coin')

To make these settings permanent, add the above 2 + 1 commands to your ~/.sage/init.sage file. Note that this setting will not affect doctesting (sage -t) because this file is ignored in doctesting mode.

Running doctests

To run the (limited) testsuite of this package, use:

$ sage setup.py test

To run the Sage testsuite with the default MIP solver set to the backend provided by this package, use:

$ sage setup.py check_sage_testsuite

Running tests with tox

The doctests can also be invoked using tox:

$ tox -e local
$ tox -e local-sage_testsuite

If you have docker installed, more tests can be run:

$ tox -e docker-sage_binary-cbc_coinbrew

See tox.ini for the available options.

Overriding the default solver by patching the Sage installation

Another method is to patch the module in permanently to the sage installation (at your own risk). This method will affect doctesting.

$ sage -c 'import os; import sage.numerical.backends as dm; import sage_numerical_backends_coin.coin_backend as sm; s = sm.__file__; f = os.path.basename(s); d = os.path.join(dm.__path__[0], f); (os.path.exists(d) or os.path.lexists(d)) and os.remove(d); os.symlink(s, d);'

Or use the script patch_into_sage_module.py in the source distribution that does the same:

$ sage -c 'load("patch_into_sage_module.py")'
Success: Patched in the module as sage.numerical.backends.coin_backend

Verify with check_get_solver_with_name.py that the patching script has worked:

$ sage -c 'load("check_get_solver_with_name.py")'
Success: get_solver(solver='coin') gives <sage_numerical_backends_coin.coin_backend.CoinBackend object at 0x7f8f20218528>