#20446: GLPKExactBackend - a variation on GLPKBackend that sets a solver
parameter
and signals errors on integer variables
-------------------------------------+-------------------------------------
Reporter: mkoeppe | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-7.2
Component: numerical | Resolution:
Keywords: lp | Merged in:
Authors: Matthias Koeppe | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/mkoeppe/glpkexactbackend___a_variation_on_glpkbackend_that_sets_a_solver_parameter_and_signals_errors_on_integer_variables|
e7a2bd7d86034b16c8407ae534d75c39956edbf4
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Description changed by mkoeppe:
Old description:
> GLPK has an exact simplex method, which can be requested by setting a
> solver parameter.
> Via #20406, a user can set this parameter.
>
> It would be more convenient to define a named backend that does that.
>
> Also, setting the solver parameter actually causes GLPK to solve the
> continuous relaxation, ignoring all integer variables. This might be
> surprising to users.
>
> {{{
> sage: delsarte_bound_additive_hamming_space(19,15,7,isinteger=True)
> 3
> sage: from sage.numerical.backends.generic_backend import get_solver
> sage: def glpk_exact_solver():
> b = get_solver(solver="GLPK")
> b.solver_parameter("simplex_or_intopt", "exact_simplex_only")
> return b
> sage:
> delsarte_bound_additive_hamming_space(19,15,7,solver=glpk_exact_solver,isinteger=True)
> glp_exact: 54 rows, 20 columns, 795 non-zeros
> ...
> 2
> }}}
>
> So there would be value in a named backend that actually signals an error
> when the user requests integer variables (like the CVXOpt and
> InteractiveLP backends do).
>
> {{{
> sage:
> delsarte_bound_additive_hamming_space(19,15,7,solver="GLPK/exact",isinteger=True)
> ValueError: This backend does not handle integer variables
> }}}
>
> While at it, could also support the "glp_simplex followed by glp_exact"
> mode that is mentioned in http://trac.sagemath.org/ticket/18735#comment:7
New description:
GLPK has an exact simplex method, which can be requested by setting a
solver parameter.
Via #20406, a user can set this parameter.
It would be more convenient to define a named backend that does that.
Also, setting the solver parameter actually causes GLPK to solve the
continuous relaxation, ignoring all integer variables. This might be
surprising to users.
{{{
sage: delsarte_bound_additive_hamming_space(19,15,7,isinteger=True)
3
sage: from sage.numerical.backends.generic_backend import get_solver
sage: def glpk_exact_solver():
b = get_solver(solver="GLPK")
b.solver_parameter("simplex_or_intopt", "exact_simplex_only")
return b
sage:
delsarte_bound_additive_hamming_space(19,15,7,solver=glpk_exact_solver,isinteger=True)
glp_exact: 54 rows, 20 columns, 795 non-zeros
...
2
}}}
So there would be value in a named backend that actually signals an error
when the user requests integer variables (like the CVXOpt and
InteractiveLP backends do).
{{{
sage:
delsarte_bound_additive_hamming_space(19,15,7,solver="GLPK/exact",isinteger=True)
ValueError: This backend does not handle integer variables
}}}
Follow-up wishlist item: #20458: GLPKBackend/GLPKExactBackend: Support
"glp_simplex followed by glp_exact"
--
--
Ticket URL: <http://trac.sagemath.org/ticket/20446#comment:8>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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