Originally posted by: anahana

Hi,

I'm solving the biella1 problem from the MIPLIB. It has 6110 binaries and 1218 continuous variables. I am observing which variables CPLEX selects for branching in a branch callback using the getBranch() method. At node 5 CPLEX selects variable S1187 which is a continuous variable with only the non-negativity constraint attached to it. Why would CPLEX select a continuous variable for branching? 

I am using strong branching strategy by the way.

Regards, 

Originally posted by: Laci Ladanyi

If you look at constraint R1187, then you can see it is an equality constraint, it has S1187 with coefficient 1, the rest of the variables in it are integers with integer coefficients, and right hand side isinteger, too. Therefore S1187 is an implied integer variable. CPLEX detects this and then S1187 is a valid candidate for branching.

--Laci

Originally posted by: anahana

You're right, I missed that. Thanks Laci!