Originally posted by: MatthiasWalter

Dear Cplex community,

I have a question regarding the cplex.getValue() statement for an IloNumVar object (C++).
In my application I solve a linear program, then I query the value of the variables x[i] via cplex.getValue(x[i]) for i=1,…I. If the value of x[i] is equal to 0, I fix the variable to 0 via x[i].setUB(0.0). After this operation, when I query the value of the next variable xi+1, Cplex will issue the error message „Cplex Error 1217: No solution exists“. Obviously, Cplex has to reoptimize the (modified) problem, before another query is possible.

I avoid the Error by first recording all the variables I want to fix and by fixing them after having queried all (and recorded some) variables.

I am wondering if it is possible to fix a variable to its current value (!) without loosing the possibility to query the values of this or other variables.
In some special applications such a possibility would save myself an extra call of cplex.solve().

I would be grateful for any advice.

Kind regards
Matthias Walter
#CPLEXOptimizers
#DecisionOptimization

Originally posted by: SystemAdmin

I would use the getValues() method to query all the variables I cared about, store their values in my code's memory space, and query that copy (rather than CPLEX) until I was ready to call solve() (at which time I might zero out those values or set a flag to indicate they are no longer to be trusted).

Paul

Mathematicians are like Frenchmen: whenever you say something to them, they translate it into their own language, and at once it is something entirely different. (Goethe)
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Originally posted by: MatthiasWalter

Dear Paul,

thanks for your helpful suggestion.

Best regards
Matthias
#CPLEXOptimizers
#DecisionOptimization