[Help-glpk] Certificates of infeasibility or unboundness

[Nathann Cohen]

Hello everybody !!!

I am working on the software Sagemath (http://www.sagemath.org/) which
uses GLPK, and I would like to get certificates of infeasibility for
LP, something like a farkas certificate. I noticed the function
glp_get_unbnd_ray, which sounds like something I may use, but I still
have not been able to devise how. As far as I understand it, it
returns the index of a variable (even though until now, it always
return 0 which is a bad sign) which may be basic or auxiliary. If I
make no mistake, basic variables (and perhaps auxiliary too ?) are
built as a linear function on the problem's variable (or the variables
of its dual). Is there any way for me to this linear function given
the index ?

I was not able to find any example of source code using
glp_get_unbnd_ray or even its former equivalent get_ray_info :-/

Thank you very much for your help ! It would be incredibly nice to
have this feature exposed in Sage :-)

Nathann Cohen
http://www-sop.inria.fr/members/Nathann.Cohen/