I am trying to get the real and imaginary part of a complex expression but it appears that the evalc(Im(F)) does not work. My guess is that i have to manipulate the expression before i use the evalc, but the simplify command for example did not give a result either. My funstion is F:=1+2*zs*I-w^2/ws^2-w^2/ws^2*ks*(1+2*zs*I)*(K3*(1+2*z3*I)-H*K2(1+2*z2*I)+H*(H*K1*(1+2*z1*I)-K2*(1+2*z2*I)))/(K1*(1+2*z1*I)*K3*(1+2*z3*I)-K2^2*(1+2*z2*I)^2);

As you see I have imaginary I...