Fix Travis CI failure (lqr bad argument)#253
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murrayrm merged 2 commits intopython-control:masterfrom Dec 22, 2018
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This was referenced Dec 21, 2018
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Fix for the Travis CI bug identified in PR #242 regarding LQR test. The problem was that one of the test cases used in
tests/matlab_test.pywas incorrect. It used a set of weighting matrices that did not give a positive definite cost function for the LQR problem. This should have generated a error, but that case is not tested in the code (see issue #252, created to track this).The fix here is to change the state space weighting matrix (multiplying it by 10) so that the overall weighting function is now positive definite. In addition, a skipped unit test has been put in with the original test case.
The reason this was generating spurious errors is because the
slycotLQR function (sb0md) was creating a closed loop system whose eigenvalues had very small realparts (on order 1e-16) and apparently these were sometimes positive and sometimes negative.Also fixed a small typo in a docstring while I was at it.