#20602: MixedIntegerLinearProgram.gen() does not do anything useful
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Reporter: mkoeppe | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.3
Component: numerical | Resolution:
Keywords: lp | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by mkoeppe:
Old description:
> As observed in the comments in #20461:
>
> {{{
> sage: mip = MixedIntegerLinearProgram(solver='GLPK')
> sage: mip.gen(0) ### Names a variable, but does not create it
> in the backend
> x_0
> sage: mip.number_of_variables()
> 0
> sage: mip[0] ### This now creates a variable. It prints
> the same as the result of gen(0), but is different.
> x_0
> sage: mip.get_values(mip.gen(0))
> [...]
> TypeError: Not a MIPVariable: x_0
> sage: mip.is_real(mip.gen(0))
> [...]
> KeyError: x_0
> sage: mip.is_real(mip[0])
> True
> }}}
New description:
As observed in the comments in #20461:
{{{
sage: mip = MixedIntegerLinearProgram(solver='GLPK')
sage: mip.gen(0) ### Names a variable, but does not create it in
the backend
x_0
sage: mip.number_of_variables()
0
sage: mip[0] ### This now creates a variable. It prints
the same as the result of gen(0), but is different.
x_0
sage: mip.get_values(mip.gen(0))
[...]
TypeError: Not a MIPVariable: x_0
sage: mip.is_real(mip.gen(0))
[...]
KeyError: x_0
sage: mip.is_real(mip[0])
True
}}}
I think mip.gen(i) should simply return the same variable that mip[i]
returns (and like mip[i], it should create this variable in the backend if
it does not exist yet).
--
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Ticket URL: <http://trac.sagemath.org/ticket/20602#comment:1>
Sage <http://www.sagemath.org>
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