[Help-gnucap] can gnucap output impedance as a function?

[Wen]

Is there a a possibility to make gnucap output the impedance of a part of an 
electric circuit as a function of the frequency? 
For example for a series connection of RC-elements (parallel) like this

   ---R1---    ---R2---
   |       |  |        |
---        ---          ---
   |       |  |        |
   ---C1---    ---C2---

it would output something like
z(freq)= R1/(1+(R1*2*pi*freq*C1)^2)+R2/(1+(R2*2*pi*freq*C2)^2) + j* 
(-(R1)^2*2*pi*freq*C1/(1+(R1*2*pi*freq*C1)^2)-(R2)^2*2*pi*freq*C2/(1+(R2*2*pi*freq*C2)^2))

So Resistors, Inductors, Capacitors and so on could be parameters and the 
frequency the variable. I need it in such a form to do a complex nonlinear 
least-square fit afterwords with experimental data to get the parameters (in 
this case R1, R2, C1 and C2) that fit best to the real system.
This will be part of an experiment with impedance spectroscopy?

Is gnucap able to give me such output? If not, can you recomend another free 
program thats able to do that?

Thanks,
Wen