#20446: GLPKExactBackend - a variation on GLPKBackend that sets a solver
parameter
and signals errors on integer variables
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Reporter: mkoeppe | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-wishlist
Component: numerical | Keywords: lp
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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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
--
Ticket URL: <http://trac.sagemath.org/ticket/20446>
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