#13148: make LP return the number of variables
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Reporter: dimpase | Owner: ncohen
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.2
Component: linear programming | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by dimpase):
Replying to [comment:4 ncohen]:
> > as far as I am concerned this is an LP with 3 variables, not 2.
> > So my code is right :–)
>
> Yeah, but itbreaks doctests.
it only does so if you hack your Sage installation to make Gurobi the
default
solver. Correct me if I'm wrong, but isn't the default LP solver GLPK?
>
> > (well, you don't have means to control that RgR0, so what?)
>
> None at all. When you add a as a constraint a linar function + two
bounds (min and max) Gurobi automatically creates a newbounded variable
and makes the constraint an equality.
> That's stupid, boring, whatever you want, but this is still how it
behaves.
Ah, I see, thanks.
>
> > When you construct the usual dual of such an LP, you'll end up with
> > a different dual.
>
> Yeah. That's why I told you by email that you would be surpised by the
behviour of some solvers on his respect.
Well, I constructed LPs that CPLEX can solve by primal simplex, but not by
the dual. LPs that CPLEX finds out to be infeasible, but for which it
fails to give you an infeasibility certificate. I don't think they can
surprise me any more :-)
Dima
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13148#comment:5>
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