Looks fine to me.

It's probably not important, but FYI: with Python 3.7 and Sphinx 2.0.1, the only python-sphinx variant I tried, I get this warning when building docs:

/home/rory/src/python-control/doc/generated/control.frd.rst: WARNING: document isn't included in any toctree

Thought I found the problem (a stray "frd" in matlab.rst instead of "FRD"), but turns out the problem was more subtle:

On MacOS (where I usually work), the file system is "case preserving" but not "case sensitive". This is a problem when you have two functions with the same name but different case. In the control package, there is a class FRD and a function frd. These conflict with each other in the generated/ subdirectory.

There was an error that was getting masked by this effect: in the documentation, we need to reference both FRD (when referring to the class) and frd (when referring to the function). The reference to the function in the "system creation" portion of the manual was FRD when it should have been frd. I've fixed that here, but it does cause a problem compiling the documentation on MacOS.

@roryyorke Can you check to see if this fix works for you (on windows or linux, I assume).

No more warning due to FRD/frd, and I can see both control.frd and control.FRD in the generated docs.