If I understand correctly, you want to use the power_zmeter command to create the impedance within a script and then plot it as well.
To do that you can follow the example as shown in the corresponding documentation page:
As the example shows, you can get the data for the impedance using the following code:
% This is from the example
Zdata = power_zmeter('power_gui',logspace(0,3,500))
where the frequency range is defined as the second argument.
Impedance is inherently a complex number so I do not understand why you need to calculate it without the imaginary part.
If you mean that you want to see the magnitude of the impedance then you can use the following command to plot your results:
plot(Zdata.Freq,abs(Zdata.Z(:,1)))
