Gurobi objective with python dictionary values

Question

I am using Gurobi 6.0 with Python 2.7. I am curious to know if Gurobi allows the objective function to have values coming from a dictionary with indices of the decision vari

Answer 1

For a somewhat complex causal chain d[(x,y)] in your code is equivalent to d[(0,1)], so the constant -5 winds up being your objective function. The reasons are

• gurobi.Var has __hash__ defined
• gurobi.Var has __cmp__ defined. It always returns a truthy object
• In your case, x and y have hash values of 0 and 1
• The python dictionary lookup algorithm resolves d[(x,y)] to d[(0,1)]

What you are trying to do doesn't fit into the integer programming framework. The best way to put this into gurobi is to add indicator variables that x and y take on specific values.