Genetic algorithm for yagi variable reaactances optimization

So I have a 3 dipole antenna array with just one excited in the middle and other two are parasities. I am trying to find the optimize value for all 3 of the reactances to get a broadside pattern. I am getting the values for self and mutual coupling impedance as imaginary and I got the respond that I can't use GA for the imaginary. Can anyone walk me through with the program. It is going to be three values for x1, x2 and x3.