Modification of RHS of constraints

[Siamak Naderi]

Dear All, 

I am writing a Benders Decomposition type of algorithm where I need to modify some constraints. At the moment I remove and add contrarians with new values which doesn't make sense (It increases the computational time). I found GBRConstr.Set(GRB.DoubleAttr.RHS, newValue)  to update the RHS but it doesn't work for me.  Here is the code. I want to update the RHS of the these two sets of constraints (x_opt is input, which causes this change). 

        psp_constr1 = {}

        psp_constr2 = {}

        for i in stores:

            for o in options:

                for k in sizes:

                     psp_constr1[i,o,k] = psp.addConstr(z[(i,o,k)] <= sum(supply[(j,o,k)]*x_opt[(j,i,o)] for j in stores) )

                    

        for i in stores:

            for j in stores:

                for o in options:

                    if i!=j:

                       psp_constr2[i,j,o] = psp.addConstr(y[(i,j)] >= x_opt[(i,j,o)] ) 

Any help is appreciated, 

SNV

[Daniel Espinoza]

SNV,

What do you mean it did not work? did you write the LP before/after the changes? Maybe you missed an update call?

Best

Daniel

[Siamak Naderi]

Dear Daniel, 

When I add "psp_constr1[0,0,0].Set(GRB.DoubleAttr.RHS, 200)" right after the constraints (as above), I receive this error: AttributeError: 'gurobipy.Constr' object has no attribute 'Set' . 

Appreciate if you could help me, 

SNV

[Siamak Naderi]

I made it using "model.setAttr("RHS", m.getConstrs(), newvalue)". 

Thanks anyways, 

[Greg DeYong]

How did you get this to work? I get an error message "gurobipy.Model object has no attribute 'setAttr'". I also get the same original error you noted before "gurobipy.Constr object has no attribute 'Set' if I try to use the approach you attempted first.

[Tobias Achterberg]

Which Gurobi version are you using? The Python API was extended quite a bit in versions
7.0 and 7.5.

Regards,

Tobias