Originally posted by: ops1234

Hi,

I am writing my whole model into a lp-file with the function CPXXwriteprob(env,lp,"myprob.lp",nullptr). In this file cplex appended #number to each variable with an increasing number for each new variable. Same thing happens with constraints. Can I somehow turn this off? I have given all my variables unique names already.

Best regards,

ops

This happens if some of your variable or constraint names are not valid for LP file format and have thus to be replaced for output. Consequently, this behavior cannot be turned off since otherwise the LP file would be incorrect.

You can find the rules for names in LP files here: https://www.ibm.com/support/knowledgecenter/SSSA5P_12.8.0/ilog.odms.cplex.help/CPLEX/FileFormats/topics/LP_VariableNames.html

Make sure all your names conform to this then no change in names should happen.

Originally posted by: ops1234

Hi,

thanks for your answer. I am not sure if I understand the rule concerning the letter e. Is something like 'vel3' or 'EXC3' allowed? Another question: If all my variables conform to the rules and have unique names, but several constraints 'of the same class' have the same name, e.g. several constraints were given the name "LINK_CONSTR", does cplex give only each constraint a #number or do the variables also get numbers?

Best regards,

ops

"vel3" is fine, "EXC3" is not (the rule says that names must not start with 'e' or 'E').

I don't think CPLEX checks for duplicate constraint names. So if you have multiple constraints with the same name then the LP file will just have multiple constraints with the same name. Same for variables.

Originally posted by: ops1234

Thank you for your quick response. I could see that cplex doesn't care about same constraint names, but same variable names could become a problem? Unless cplex saves and works with its own variable identifiers and the user defined names are only for output. Well I guess I will see when I change the names. Nonetheless, thank you very much, this helped a lot. 

Yes, duplicate variable names can easily become a problem. CPLEX will happily write these variables to the LP file -- with the same name! Any reader can then of course not distinguish the two variables and will thus merge them into one. This will result in a different model. Thus duplicate variable names must be avoided.