PPL backend re-solves the problem every time get_variable_value or get_objective_value is called

[mkoeppe]

The PPL backend sets up a new PPL problem and re-solves it from scratch every time that get_variable_value or get_objective_value is called.

sage: p = MixedIntegerLinearProgram(solver='ppl', maximization=True)
sage: x = p.new_variable()
sage: p.set_objective(p.sum((i+20)*x[i] for i in range(1000)))
sage: p.add_constraint(p.sum((i+15)*x[i] for i in range(1000)), max=20000)
sage: x.set_max(1)
sage: p.solve()  # takes a few seconds
11438750/507
sage: p.get_objective_value()  # takes a few seconds, should be instant
11438750/507
sage: p.get_values(x)  # takes forever, should be instant

CC: @dimpase @videlec @jdemeyer

Component: numerical

Author: Matthias Koeppe

Branch/Commit: df42b5b

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/20361

[dimpase]

comment:1

oh, great catch, I was always wondering why get_values is so bloody slow with ppl...

[mkoeppe]

Branch: u/mkoeppe/ppl_backend_re_solves_the_problem_every_time_get_variable_value_or_get_objective_value_is_called

[mkoeppe]

Commit: df42b5b

[mkoeppe]

New commits:

df42b5b

Fix for #20361: PPL backend re-solves the problem every time get_variable_value or get_objective_value is called

[dimpase]

Author: Matthias Koeppe

[dimpase]

comment:4

Great!

[dimpase]

Reviewer: Dima Pasechnik

[vbraun]

Changed branch from u/mkoeppe/ppl_backend_re_solves_the_problem_every_time_get_variable_value_or_get_objective_value_is_called to df42b5b