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Add unit test illustrating issue #935 + add method keyword for tf2ss#937
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murrayrm merged 3 commits intopython-control:mainfrommurrayrm:tf2ss_unstable_bug-21Oct2023Nov 8, 2023
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47 changes: 37 additions & 10 deletionscontrol/statesp.py
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -60,10 +60,10 @@ | ||
| from scipy.signal import StateSpace as signalStateSpace | ||
| from warnings import warn | ||
| from .exception import ControlSlycot, slycot_check, ControlMIMONotImplemented | ||
| from .frdata import FrequencyResponseData | ||
| from .lti import LTI, _process_frequency_response | ||
| from .iosys import InputOutputSystem, common_timebase, isdtime,issiso,\ | ||
| _process_iosys_keywords, _process_dt_keyword, _process_signal_list | ||
| from .nlsys import NonlinearIOSystem, InterconnectedSystem | ||
| from . import config | ||
| @@ -1583,6 +1583,13 @@ def ss(*args, **kwargs): | ||
| -------- | ||
| tf, ss2tf, tf2ss | ||
| Notes | ||
| ----- | ||
| If a transfer function is passed as the sole positional argument, the | ||
| system will be converted to state space form in the same way as calling | ||
| :func:`~control.tf2ss`. The `method` keyword can be used to select the | ||
| method for conversion. | ||
| Examples | ||
| -------- | ||
| Create a Linear I/O system object from matrices. | ||
| @@ -1615,10 +1622,13 @@ def ss(*args, **kwargs): | ||
| warn("state labels specified for " | ||
| "non-unique state space realization") | ||
| # Allow method to be specified (eg, tf2ss) | ||
| method = kwargs.pop('method', None) | ||
| # Create a state space system from an LTI system | ||
| sys = StateSpace( | ||
| _convert_to_statespace( | ||
| sys, method=method, | ||
| use_prefix_suffix=not sys._generic_name_check()), | ||
| **kwargs) | ||
| @@ -1765,6 +1775,10 @@ def tf2ss(*args, **kwargs): | ||
| name : string, optional | ||
| System name. If unspecified, a generic name <sys[id]> is generated | ||
| with a unique integer id. | ||
| method : str, optional | ||
| Set the method used for computing the result. Current methods are | ||
| 'slycot' and 'scipy'. If set to None (default), try 'slycot' first | ||
| and then 'scipy' (SISO only). | ||
| Raises | ||
| ------ | ||
| @@ -1781,6 +1795,13 @@ def tf2ss(*args, **kwargs): | ||
| tf | ||
| ss2tf | ||
| Notes | ||
| ----- | ||
| The ``slycot`` routine used to convert a transfer function into state | ||
| space form appears to have a bug and in some (rare) instances may not | ||
| return a system with the same poles as the input transfer function. | ||
| For SISO systems, setting ``method=scipy`` can be used as an alternative. | ||
| Examples | ||
| -------- | ||
| >>> num = [[[1., 2.], [3., 4.]], [[5., 6.], [7., 8.]]] | ||
| @@ -2189,7 +2210,7 @@ def _f2s(f): | ||
| return s | ||
| def _convert_to_statespace(sys, use_prefix_suffix=False, method=None): | ||
| """Convert a system to state space form (if needed). | ||
| If sys is already a state space, then it is returned. If sys is a | ||
| @@ -2213,13 +2234,17 @@ def _convert_to_statespace(sys, use_prefix_suffix=False): | ||
| raise ValueError("transfer function is non-proper; can't " | ||
| "convert to StateSpace system") | ||
| if method is None and slycot_check() or method == 'slycot': | ||
| if not slycot_check(): | ||
| raise ValueError("method='slycot' requires slycot") | ||
| from slycot import td04ad | ||
| # Change the numerator and denominator arrays so that the transfer | ||
| # function matrix has a common denominator. | ||
| # matrices are also sized/padded to fit td04ad | ||
| num, den, denorder = sys.minreal()._common_den() | ||
| num, den, denorder = sys._common_den() | ||
| # transfer function to state space conversion now should work! | ||
| ssout = td04ad('C', sys.ninputs, sys.noutputs, | ||
| @@ -2230,9 +2255,8 @@ def _convert_to_statespace(sys, use_prefix_suffix=False): | ||
| ssout[1][:states, :states], ssout[2][:states, :sys.ninputs], | ||
| ssout[3][:sys.noutputs, :states], ssout[4], sys.dt) | ||
| elif method in [None, 'scipy']: | ||
| # Scipy tf->ss can't handle MIMO, but SISO is OK | ||
| maxn = max(max(len(n) for n in nrow) | ||
| for nrow in sys.num) | ||
| maxd = max(max(len(d) for d in drow) | ||
| @@ -2244,12 +2268,15 @@ def _convert_to_statespace(sys, use_prefix_suffix=False): | ||
| D[i, j] = sys.num[i][j][0] / sys.den[i][j][0] | ||
| newsys = StateSpace([], [], [], D, sys.dt) | ||
| else: | ||
| if not issiso(sys): | ||
| raise ControlMIMONotImplemented( | ||
| "MIMO system conversion not supported without Slycot") | ||
| A, B, C, D = \ | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. Suggested change for the two lines above: | ||
| sp.signal.tf2ss(squeeze(sys.num), squeeze(sys.den)) | ||
| newsys = StateSpace(A, B, C, D, sys.dt) | ||
| else: | ||
| raise ValueError(f"unknown {method=}") | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others.Learn more. First instantiation of self-documenting F-strings in python-control? : ) | ||
| # Copy over the signal (and system) names | ||
| newsys._copy_names( | ||
4 changes: 2 additions & 2 deletionscontrol/tests/convert_test.py
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46 changes: 46 additions & 0 deletionscontrol/tests/statesp_test.py
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