Might be due to roundoff issue (?). PPL does exact solving (using
rationals from GMP) while GLPK works with floating point numbers.
Though, on such small instance it looks suspicious that floating point
are to blame (especially if CBC/Coin works fine). Is there a Sage ticket
open? Was it reported to GLPK?
On 19/08/2017 20:15, fidelbc wrote:
Hello All,
Seems like the `fractional_chromatic_index` method for graphs contains a
bug.
The implementation contains an infinite loop that is broken when a quantity
is less than or equal to 1, however the loop never ends on the following
input:
sage: g=graphs.PetersenGraph()
sage: g.fractional_chromatic_index(solver="GLPK")
The problem seems to depend on the LP solver, using PPL seems to work just
fine. Issue seems to be GLPK and CBC/Coin.
This was originally reported by elbie at a question in ask.sagemath, see
[1].
Thanks,
fidel
[1]:
https://ask.sagemath.org/question/38543/fractional_chromatic_index-in-sage-76-gets-stuck-in-loop-adding-constraints/
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