As I just posted on the ML, I would rather call this function `freqresp` or some similar name conveying the idea of frequency response. I would change the docstring accordingly by renaming the `nyq` variable into `H` (or `G` since G(s) is mentionned in the Example)

reference in Matlab documentation : http://www.mathworks.fr/fr/help/control/ref/freqresp.html

Otherwise, looks good to me !