I have implemented a MIP-model in GAMS, which I would like to solve to proven optimality. The problem is degenerate and has a lot optimal solutions, and many solutions very close to the optimum. It is not terminating with the optimal solution, but continuing to examine nodes with a very small gap > 0.00 %. I have a good idea for a branching rule, which I believe can work around the degeneracy problems. Instead of doing binary branching on fractional binary variables, I intend to branch on the sum of some variables, i.e: *sum(s, delta(s)) =l= k;* or *sum(s, delta(s)) =g= k+1;*

How can I introduce such a branching rule in GAMS, instead of just using binary branching ?