Add test for Nyquist evaluation at a pole by murrayrm · Pull Request #1104 · python-control/python-control
This PR addresses #1103 by adding a check and raising an exception if the Nyquist contour includes a pole. In this case the Nyquist curve is not well defined and hence an exception is raised. (As noted in #1103, this case was already raising an exception, but not quite for the right reason.)
Unit test added that covers the situation.