Get an instance to inherit another instance's constraints in pyomo

Question

I'm trying to create an instance that inherits another instance's constraints, whilst adding some new ones.

Is there a way to "copy" the previous instance's constraints into the new one?

Here's a snippet from the code

...
model.bnb_bound_constraints = ConstraintList()
...

non_solved_instances = []
bnb_end = False
incumbent_value = 0
solve_counter = 0
integer_variables_list = []

bnb_instance = model.create_instance(data)
variables_list = [bnb_instance.x]
non_solved_instances.append(bnb_instance) 

while bnb_end != True:

    solve_counter += 1
    print len(non_solved_instances), "Non solved instance(s)"
    bnb_solve = optsolver.solve(non_solved_instances[0], tee = False)
    print "Objective value for instance", solve_counter,":",value(non_solved_instances[0].obj)

    if value(non_solved_instances[0].obj.sense)*value(non_solved_instances[0].obj) <= value(non_solved_instances[0].obj.sense)*incumbent_value:

        incumbent_value = 2000

        for new_instance in range(2):

            bnb_instance = model.create_instance(data)
            variables_list = [bnb_instance.x]

            for con in non_solved_instances[0].bnb_bound_constraints:
                bnb_instance.bnb_bound_constraints.add(non_solved_instances[0].bnb_bound_constraints[con].expr)
                #This is what ive been trying to do to copy the constraints, doesnt work though.

            if new_instance == 0:
                bnb_instance.bnb_bound_constraints.add(expr = bnb_instance.x[solve_counter] <= floor(value(non_solved_instances[0].x[solve_counter])))
                #adds a new constraint to bnb_instance

            elif new_instance == 1:
                bnb_instance.bnb_bound_constraints.add(expr = bnb_instance.x[solve_counter] >= ceil(value(non_solved_instances[0].x[solve_counter]))) 
                #adds a new constraint to bnb_instance

            non_solved_instances.append(bnb_instance)

    del non_solved_instances[0]

    if len(non_solved_instances) == 0 or solve_counter >= 20:
        bnb_end = True

non_solved_instances[0] contains the "original" instance, whose constraints i wish to inherit to bnb_instance

Cheers!

Answer 1

One way would be to clone the entire model and then add additional constraints to the clone

m = ConcreteModel()
# Add stuff to m

m2 = m.clone()
m2.c2 = Constraint(expr=m2.x**2<=10)