#15691: mip backends: bug due to bool/number confusion
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Reporter: equaeghe | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.1
Component: PLEASE CHANGE | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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(I only have the GLPK backend installed, so I actually only tested with
that.)
In all the mip backends, the methods `variable_upper_bound` and
`variable_lower_bound` contain essentially the statement `value == False`.
This causes it to be impossible to set variable bounds to 0.0, as `0.0 ==
False` is `True`.
Illustrated in the console:
{{{
sage: version()
'Sage Version 6.0, Release Date: 2013-12-17'
sage: p = MixedIntegerLinearProgram()
sage: p.set_objective(p[0])
sage: p.show()
Maximization:
x_0
Constraints:
Variables:
x_0 is a continuous variable (min=0.0, max=+oo)
sage: p.set_max(p[0], 0.0) # fails
sage: p.show()
Maximization:
x_0
Constraints:
Variables:
x_0 is a continuous variable (min=0.0, max=+oo)
}}}
A simple fix is to replace all(?) occurrences of `value == False` by
`value is False`.
--
Ticket URL: <http://trac.sagemath.org/ticket/15691>
Sage <http://www.sagemath.org>
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