counting infeasible solutions in GAMS software

Question

I want to run several mathematical models in GAMS and count the number of infeasible solutions. How should I write the condition of IF statement?

Answer 1

You can check the modelstat attribute of your models after solving them. Here is a little example:

equation obj;
variable z;
positive variable x;

obj.. z =e= 1;

equation feasible;
feasible..    x =g= 1;

equation infeasible1;
infeasible1.. x =l= -1;

equation infeasible2;
infeasible2.. x =l= -2;

model m1 /obj, feasible   /;
model m2 /obj, infeasible1/;
model m3 /obj, infeasible2/;

scalar infCount Number of infeasible models /0/;

solve m1 min z use lp;
if(m1.modelstat = %ModelStat.Infeasible%, infCount = infCount+1;)

solve m2 min z use lp;
if(m2.modelstat = %ModelStat.Infeasible%, infCount = infCount+1;)

solve m3 min z use lp;
if(m3.modelstat = %ModelStat.Infeasible%, infCount = infCount+1;)

display infCount;

If you have an integer problem you should also check for %ModelStat.Integer Infeasible% and not only %ModelStat.Infeasible%, so the check after a solve could become

solve m3 min z use mip;
if(m3.modelstat = %ModelStat.Infeasible% or m3.modelstat = %ModelStat.Integer Infeasible%,
  infCount = infCount+1;
)

I hope, that helps! Lutz