Feature/check dimension function - #269

Coverage increased (+0.2%) to 78.543% when pulling 7859f8c on don4get:feature/check-dimension-function into 31e6944 on python-control:master.

I don't understand why this functionality is useful? It seems like it is just adding a function that is not likely to be used by users?

Hello! Thank you for your review ;)

As I said in the description of the PR, the point here is to create an internal function to make dimension check uniform in the library.

Currently, the check is partial and varies from a control function to another:
in statefbk.py -> place:

if A_mat.shape[0] != A_mat.shape[1]:
            raise ControlDimension("A must be a square matrix. "
                                   "rows: {} != columns: {}".format(A_mat.shape[0],
                                                                    A_mat.shape[1]))

        if A_mat.shape[0] != B_mat.shape[0]:
            raise ControlDimension("The number of rows of A ({}) must equal "
                                   "the number of rows in B ({})".format(A_mat.shape[0],
                                                                         B_mat.shape[0]))

in place_varga:

if A_mat.shape[0] != A_mat.shape[1] or A_mat.shape[0] != B_mat.shape[0]:
        raise ControlDimension("Matrix dimensions are incorrect.")

in lqr:

# Check dimensions for consistency
    nstates = B.shape[0]
    ninputs = B.shape[1]
    # TODO: Create / Figure out a generic function to check for inconsistent system
    if A.shape[0] != nstates or A.shape[1] != nstates:
        raise ControlDimension("Inconsistent system dimensions.")

And it continues like this in the entire library.

With this new internal function, the check will be uniform, factorized and unit tested :)

If we are going to include this PR, a couple of requests:

• Please see review comments and address as needed.

• I think we should also find the spots in the current code that would use this functionality and add it to those portions of the code. That way we know the new functionality actually does something useful (and works in the places where we need it).

• Need to resolve conflicts with current master.

PR has been idle for > 6 months => stale. @don4get I will close this PR in a few days unless you will have time to work on it soon. No worries if not; just re-open when you have responded to the comments above.