[Help-glpk] Dual Cost calculations

[Chris Kafka]

I have been using GLPK to experiment with some Active Constraint methods 
for MIP solving. Several of these methods rely on the dual cost returned 
by GLPK for individual constraints in a particular node. I am finding 
that on the nodes of certain problems, GLPK is claiming that every 
active constraint has a dual cost of zero.

As such, I was wondering how GLPK is calculating the dual cost, and if 
this high rate of zero dual costs sounds reasonable?

The problem that this is easiest to examine this on is the "pk1.mps" 
from the MIPLib2003 problem set. The very first node is returning 15 
zero-valued dual costs for the first node.

There's also the chance that I've managed to break GLPK while fiddling 
with the code, so any help would be appreciated. I believe I am based 
off of the GLPK 4.7 code.

Thanks very much,

--
Chris Kafka
address@hidden