From Roberto Bucher:

"rlocus" creates automatically a vector with the k values, if not provided. "root_locus" should have the possibility to pass kvect=None, but it is not accepted (-> error). It can be simply solved by adding the same lines as in rlocus, before finding a better algorithm to get the k values

#! TODO: update with a smart calculation of the gains using sys poles/zeros
if klist == None:
klist = logspace(-3, 3)