#12533: arbitrary precision LP solver backend
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Reporter: dimpase | Owner: ncohen
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: linear programming | Keywords: arbitrary precision, LP
Work_issues: | Upstream: N/A
Reviewer: David Coudert | Author:
Merged: | Dependencies:
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Changes (by ptrrsn_1):
* status: needs_work => needs_review
Comment:
Replying to [comment:15 dcoudert]:
> Hello,
>
> I can install the patch on sage-5.0.beta8 and all long tests are OK (all
involved files).
> The documentation is build correctly and displayed properly.
>
> However, I did some test based on the example of the `optimizing_point`
function and got a segfault...
> {{{
> sage: from sage.libs.ppl import Variable, Constraint_System, MIP_Problem
> sage: x = Variable(0)
> sage: y = Variable(1)
> sage: m = MIP_Problem()
> sage: m.add_space_dimensions_and_embed(2)
> sage: m.add_constraint(x >= 0)
> sage: m.add_constraint(y >= 0)
> sage: m.add_constraint(3 * x + 5 * y <= 10)
> sage: m.set_objective_function(x + y)
> sage: m.optimizing_point()
> [10/3, 0]
> sage: z = Variable(2)
> sage: m.add_constraint(z >= -3)
> terminate called after throwing an instance of 'std::invalid_argument'
> what(): PPL::MIP_Problem::add_constraint(c):
> c.space_dimension() == 3 exceeds this->space_dimension == 2.
> ...
> /path-to-sage/sage-5.0.beta8/spkg/bin/sage: line 308: 29045 Aborted
(core dumped) sage-ipython "$@" -i
> }}}
>
> Some tests should be added somewhere.
Hi, thanks for your feedback!
It is actually not a bug. The statement
"m.add_space_dimensions_and_embed(2)" increases the space dimension of the
MIP_Problem from 0 (default) to 2. However, z is a variable in the third
dimension (the number 2 in "z = Variable(2)" means the dimension of this
variable is 2, which means it is in the third dimension since the
numbering starts from zero). Since the dimension of the variable exceeds
the space dimension of the MIP_Problem, it gives error.
An extra line should be added to make it works:
sage: z = Variable(2)
sage: m.add_space_dimensions_and_embed(1)
sage: m.add_constraint(z >= -3)
> This will be a great patch!
Thank you!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12533#comment:16>
Sage <http://www.sagemath.org>
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