Originally posted by: Atefeh alizadeh

Hello,

I want to build a CPLEX model using Python where some of the parameters of the model change (NOT a sensitivity analysis) and each different value is dictated by information at a node of the BB. So, I do not want to build a model from ground up at each node, rather I want to pass a previously built model and just change a few parameters and solve it. Is it possible to introduce parameters in the model so that before solving it I just set the value of the parameter and CPLEX solves it? Or I  need to build the whole model every time I have a different value for the parameters? The goal is to save time by avoiding to build the model every time a small number of parameters change.

I tried to solve this problem using following code:

cpx1 = cplex.Cplex()
# do stuff
cpx1.parameters.write_file('tmp.prm')
cpx1.write('tmp.sav')

cpx2 = cplex.Cplex()
cpx2.parameters.read_file('tmp.prm')
cpx2.read('tmp.sav')

because I could not find some thing like cpx2 = cpx1.copy() in Cplex and then I tried to modify the model at each node. but I get this error:

CPLEX Error  1219: No names exist.

Is there any other way to handle this or solve the error?

Thank you in advance

With regards to your first question, you can clone model with the following syntax:

cpx2 = cplex.Cplex(cpx1)

As for the 1219 error, can you show us the full traceback and the code that triggers it? Even though you created a copy of the model using SAV files (and this required some disk I/O), it should still give you a more or less exact copy (including names from the original model). So, the error doesn't make sense without more details.

Originally posted by: Atefeh alizadeh

Thanks for your quick reply. I am calling it in a user cut call back and I get the attached error.

Can you wrap your callback code into a try/expect statement, catch the exception in the except block, print its message and stack-trace and then re-throw it? That would give a better idea at where exactly the error is triggered. Could you please also show the offending code then?

Wrap your callback like so:

import traceback
try:
    # Your callback code here
    ...
except:
    traceback.print_exc()
    raise

Originally posted by: Atefeh alizadeh

Hello. Actually I solved the issue by cpx2=cplex.cplex(cpx1). Thank you so much.