nequality constraints, on the other hand, must be real.
S is declared complex, so Sumvector’*S is complex, which therefore can’'t be in an inequality constraint… Hence the error. I don’t know how the code should be changed because I don’t know what your model is supposed to be.
If the program made it to S(i,:) >= 0;the same error message would be generated. Note that instead of using a for loop, you could more simply write this without a for loop as S >= 0 . But that would also generate the same error message.