Hi,
The point is that you are not able anymore to use variables from other
problems. Namely "assignment" is a variable from "p" not "p_new".
Vincent
On 12/05/16 02:18, 'Martin R' via sage-devel wrote:
Hi there!
I am having a severe problem with a program of mine that stopped working,
very likely after upgrading to 7.2.beta5, but I'm afraid I don't know from
which version. (I believe something after 7.1)
The error I get is:
ValueError: Variable MIPVariable of dimension 1 is a variable from a
different problem
What I want to do is: check whether a MILP has a solution, and if so, check
whether it still has a solution if I add a further constraint. The MILP's
take a very long time to solve.
What I do and what worked until very recently is roughly:
p = MixedIntegerLinearProgram(constraint_generation=True,
solver="CPLEX") # solver="GLPK") # twice as long #
assignment = p.new_variable(binary=True)
p.add_constraint(... some relations in terms of assignment[box, colour]
... )
p.solve()
for (box, colour) in large_list:
p_new = copy(p)
p_new.add_constraint(assignment[box, colour] == 0)
try:
p_new.solve()
bang!
What should I do?
I don't have a minimal example exhibiting the error, but if absolutely
needed, I'd try to create one.
Many thanks,
Martin
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