[Bug-glpk] [Fwd: Possible GLPK - Sensitivity Report Bug]

[Andrew Makhorin]

-------- Forwarded Message --------
From: Melih Ozlen <address@hidden>
To: address@hidden
Subject: Possible GLPK - Sensitivity Report Bug
Date: Fri, 2 Sep 2011 11:00:04 +1000

Hi,


I'm not sure whether if it's an already reported bug (or maybe it's not
a bug either), I'm teaching GLPK as a part of my linear programming
subject, as a part of our discussion we need to get the sensitivity
reports, they show the right values for most parts but fail to show the
right range values for certain things, specifically,


* when there is slack/surplus within a constraint, it returns an
activity range not including the initial value, so is misleading for
inexperienced students as the range should actually be between the
initial value and the current level of activity, objective value at
break points also returns misleading values based on this, they should
be equal to the initial optimal value,


* for a nonbasic variable the objective value at break points should be
equal to the initial optimal value, however it returns two other values,
again misleading for inexperienced students,


* and as a suggestion for improvement is it possible to have no activity
ranges for columns, and no objective coefficient ranges for rows, again
it can be quite misleading for inexperienced students,


I'm not sending any problem instances as these happen for all problems
in general, but please let me know if you need an instance.


If they actually are bugs or areas that needs to be improved I would
love to help you as much as I can, please let me know how,


Regards,


melih