Originally posted by: Yanis.hs

Hello every body,

I had a problem with simple optimization :

Minimize 

None

subject to 

Cin_CO2Calculation(0):      CinCO2(1)=-300

Cin_CO2Calculation(1):      0.000648862 CinCO2(1) + 0.000277 CinCO2(2)=0.5876

Cin_CO2Calculation(2):      0.000648862 CinCO2(2) + 0.000277 CinCO2(3)=0.5876

Cin_CO2Calculation(3):      0.000648862 CinCO2(3) + 0.000277 CinCO2(4)=0.5876

Cin_CO2Calculation(4):      0.000648862 CinCO2(4) + 0.000277 CinCO2(5)=0.5876

End 

CPLEX told me that there is no solution for this problem. After checks, I understand that CPLEX consider all variables positives and this is why it does not find solution. Please let me know how I can solve this problem.

Regards, 

By definition of the LP format, if a variable does not appear in the 'Bounds' section (in your case there is no 'Bounds' section, so no variable appears in such a section), then its bounds are [0, infinity[. If you want to have other bounds then you have to list the variable in a 'Bounds' section with appropriate bounds.

In case you did not create this LP file manually then double check the code that creates it and make sure you create the variables with the bounds as desired (in many connectors like C++ and Java specifying no bounds for the constructor of a variable will result in default bounds 0 and infinity).