#20315: Plot knots, build knots documentation when CPLEX is installed
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Reporter: jhpalmieri | Owner:
Type: defect | Status: needs_review
Priority: blocker | Milestone: sage-7.2
Component: algebraic | Resolution:
topology | Merged in:
Keywords: | Reviewers:
Authors: Vincent Delecroix | Work issues:
Report Upstream: N/A | Commit:
Branch: | 7b79579a1df40f0ef08f0a0ac31a76646b5adc6b
u/vdelecroix/20315 | Stopgaps:
Dependencies: |
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Changes (by vdelecroix):
* component: documentation => algebraic topology
Old description:
> The presence of the solver `CPLEX` breaks plotting of knots and links:
> see [https://groups.google.com/d/msg/sage-devel/ryq2Pmn_lRY/a3twFJNUDwAJ
> sage-devel].
>
> Minimal example
> {{{
> sage: L = Link([[2,1,4,5], [5,6,7,3], [6,4,1,9], [9,2,3,7]])
> sage: L.plot()
> Traceback (most recent call last):
> ...
> MIPSolverException: 'CPLEX: The primal has no feasible solution'
> }}}
> the corresponding LP problem is
> {{{
> Constraints:
> 1 <= x_i <= infinity (for i = 0,...,19)
> x_0 - x_4 = 0
> x_1 - x_5 = 0
> - x_10 + x_12 = 0
> - x_3 + x_11 = 0
> - x_2 + x_3 = 0
> x_6 = 0
> x_2 - x_14 = 0
> x_1 - x_15 + x_16 = 0
> x_0 - x_17 = 0
> x_13 - x_16 = 0
> x_7 - x_9 = 0
> - x_5 + x_8 - x_18 = 0
> x_6 - x_18 = 0
> - x_4 + x_19 = 0
> }}}
New description:
The presence of the solver `CPLEX` breaks plotting of knots and links: see
[https://groups.google.com/d/msg/sage-devel/ryq2Pmn_lRY/a3twFJNUDwAJ sage-
devel].
Minimal example
{{{
sage: L = Link([[2,1,4,5], [5,6,7,3], [6,4,1,9], [9,2,3,7]])
sage: L.plot()
Traceback (most recent call last):
...
MIPSolverException: 'CPLEX: The primal has no feasible solution'
}}}
The reason is that the code in `Link.plot` assumes that the optimization
is over integer valued variables which is not the case by default.
We also simplify and optimize the usage of the MILP solver.
--
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Ticket URL: <http://trac.sagemath.org/ticket/20315#comment:9>
Sage <http://www.sagemath.org>
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