As described in issue #459 and PR #498, there are a number of type conversions for various overloaded operators that are not yet implemented. A table of the current and desired operations can be found in control/tests/type_conversion_test.py.

A few of the more useful ones:

• SISO StateSpace objects should be allowed to serve as a quotient under appropriate circumstances (so that you can write things like T = P*C/(1 + P*C) with state space objects, as you currently can with transfer functions.
• FrequencyResponseData and InputOutputSystem objects should be able to interact with floats and arrays.
• InputOutputSystem objects should be able to interact with LTI systems by converting the LTI system into a LinearIOSystem.
• FrequencyResponseData systems should be able to be combined with StateSpace and TransferFunction options by evaluating the state space system or transfer function at the FRD frequencies.