Fix typo in ICSystem updfcn, outfcn: update_params -> _update_params by murrayrm · Pull Request #990

Fix typo in ICSystem updfcn, outfcn: update_params -> _update_params by murrayrm · Pull Request #990 · python-control/python-control

This PR fixes a bug in the InterconnectedSystem class, where the updfcn and outfcn methods call update_params instead of _update_params. This bug didn't who up because there were no direct calls to updfcn and outfcn for an IC system. However, these show up in the new phaseplot module code, so it can generate a error.

Simple fix; just adding an underscore in two places (and a unit test to uncover the bug).