#12309: GLPK crashes or hangs on certain inputs
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Reporter: john_perry | Owner: ncohen
Type: defect | Status: new
Priority: major | Milestone: sage-5.0
Component: linear programming | Keywords:
Work_issues: | Upstream: Reported upstream.
Developers deny it's a bug.
Reviewer: | Author:
Merged: | Dependencies:
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The attached sage script (`inhomogeneous_bug_test.py`) creates a linear
system that
* crashes Sage if the variables are continuous, and
* hangs Sage if the variables are integer.
Nathann determined that this was a bug with GLPK, the underlying solver. I
have attached a C++ program (`glpk_bug.cpp`) that reproduces the bug
directly via the GLPK library, and passed it on to the developers.
I can't resist the temptation to say that the developers don't consider
this a bug, but a feature; see
[http://lists.gnu.org/archive/html/bug-glpk/2012-01/threads.html This
thread on the bug-glpk mailing list archive]
and
[http://en.wikibooks.org/wiki/GLPK/Known_issues#Unbounded_integer_variables
GLPK/Known Issues]
where they call this behavior ''essentially innate.'' The workaround is to
set upper bounds.
Sage's documentation should provide this information to the user, and
suggest the workaround. We should also try trapping the exception, and
notifying the user.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12309>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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