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Implemement lft (Linear Fractional Transform) for state-space systems#245

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murrayrm merged 5 commits intopython-control:masterfrom
hungpham2511:master
Apr 7, 2019
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Implemement lft (Linear Fractional Transform) for state-space systems#245
murrayrm merged 5 commits intopython-control:masterfrom
hungpham2511:master

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@hungpham2511 hungpham2511 commented Nov 14, 2018

The lft interconnection is implemented. Some test cases, which are generated using matlab's lft functionality, are also included.

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coveralls commented Nov 14, 2018

Coverage Status

Coverage increased (+0.2%) to 79.113% when pulling 084727c on hungpham2511:master into 4b0101c on python-control:master.

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coveralls commented Nov 14, 2018

Coverage Status

Coverage increased (+0.2%) to 79.113% when pulling 084727c on hungpham2511:master into 4b0101c on python-control:master.

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coveralls commented Nov 14, 2018

Coverage Status

Coverage increased (+0.2%) to 79.113% when pulling 084727c on hungpham2511:master into 4b0101c on python-control:master.

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coveralls commented Nov 14, 2018

Coverage Status

Coverage increased (+0.2%) to 79.113% when pulling 084727c on hungpham2511:master into 4b0101c on python-control:master.

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coveralls commented Nov 14, 2018

Coverage Status

Coverage increased (+0.2%) to 79.113% when pulling 084727c on hungpham2511:master into 4b0101c on python-control:master.

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coveralls commented Nov 14, 2018

Coverage Status

Coverage increased (+0.2%) to 79.113% when pulling 084727c on hungpham2511:master into 4b0101c on python-control:master.

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coveralls commented Nov 14, 2018 •
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Coverage Status

Coverage increased (+0.2%) to 78.424% when pulling 5955fd2 on hungpham2511:master into bcf5382 on python-control:master.

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hungpham2511 commented Nov 14, 2018

Error on testLQR.py. Strange, since the PR does not even touch this part of the code base.

The error, which is reported below, seems similar the error observed in PR #242

======================================================================
ERROR: testLQR (control.tests.matlab_test.TestMatlab)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/python-control/python-control/control/tests/matlab_test.py", line 418, in testLQR
    np.eye(1), [[1], [1], [2]])
  File "/home/travis/build/python-control/python-control/control/statefbk.py", line 325, in lqr
    X,rcond,w,S,U,A_inv = sb02md(nstates, A_b, G, Q_b, 'C')
  File "/home/travis/miniconda/envs/test-environment/lib/python3.5/site-packages/slycot/synthesis.py", line 350, in sb02md
    raise e
ValueError: the Hamiltonian or symplectic matrix H has less than n stable eigenvalues

murrayrm
murrayrm reviewed Dec 21, 2018
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Some small suggestions for improvements.

This PR seems to have pulled in some other PRs => we may see an issue when merging...

control/statesp.py
"""Return the Linear Fractional Transformation.

See definition here:
https://www.mathworks.com/help/control/ref/lft.html
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Can we reference a textbook or some other more "definitive" source for the definition of LFT?

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@hungpham2511 hungpham2511 Jan 4, 2019

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A definition can be found in the Appendix of Skogestad's Multivariable Feedback Control.

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murrayrm commented Jan 4, 2019

@hungpham2511 Can you rebase this against the current master and also address comments above?

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hungpham2511 commented Jan 4, 2019 via email

@murrayrm murrayrm added this to the 0.8.2 milestone Apr 7, 2019
@murrayrm murrayrm merged commit 3738718 into python-control:master Apr 7, 2019
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