so in the big picture, i have a transfer function and i am wanting to determine it magnitude and eventually later on do some optimization of the function but now i just want to get the real and imaginary parts of the function.  So here is my function:

>tf:=-M[tot](I*C[P]*omega+1/R[eq])/(-I*M[tot]*C[p]*omega^3-(M[tot]/R[eq]+2*Zeta*omega[n]*C[p])*omega^2+I*(omega[n]^2*M[tot]*C[p]+2*Zeta*omega[n]*M[tot]/R[eq]-Theta^2)*omega+omega[n]^2*M[tot]/R[eq])