[python-control-discuss] SF.net python-control commit:[299] trunk

[<re...@us...>]

Revision: 299
          http://sourceforge.net/p/python-control/code/299
Author:   repa
Date:     2014-05-23 12:41:47 +0000 (Fri, 23 May 2014)
Log Message:
-----------
Added c2d functionality for MIMO state-space systems; both in matlab mode
and for python mode; added tests for same

Modified Paths:
--------------
    trunk/src/dtime.py
    trunk/src/matlab.py
    trunk/src/statesp.py
    trunk/tests/discrete_test.py
    trunk/tests/matlab_test.py

Modified: trunk/src/dtime.py
===================================================================
--- trunk/src/dtime.py	2014-03-23 20:39:48 UTC (rev 298)
+++ trunk/src/dtime.py	2014-05-23 12:41:47 UTC (rev 299)
@@ -94,11 +94,25 @@
     if not isctime(sysc):
         raise ValueError("First argument must be continuous time system")
 
-    # TODO: impelement MIMO version
+    # If we are passed a state space system, convert to transfer function first
+    if isinstance(sysc, StateSpace) and method == 'zoh':
+        
+        try:
+            # try with slycot routine
+            from slycot import mb05nd
+            F, H = mb05nd(sysc.A, Ts)
+            return StateSpace(F, H*sysc.B, sysc.C, sysc.D, Ts)
+        except ImportError: 
+            if sysc.inputs != 1 or sysc.outputs != 1:
+                raise TypeError(
+                    "mb05nd not found in slycot, or slycot not installed")
+            
+    # TODO: implement MIMO version for other than ZOH state-space
     if (sysc.inputs != 1 or sysc.outputs != 1):
         raise NotImplementedError("MIMO implementation not available")
 
-    # If we are passed a state space system, convert to transfer function first
+    # SISO state-space, with other than ZOH, or failing slycot import, 
+    # is handled by conversion to TF
     if isinstance(sysc, StateSpace):
         warn("sample_system: converting to transfer function")
         sysc = _convertToTransferFunction(sysc)

Modified: trunk/src/matlab.py
===================================================================
--- trunk/src/matlab.py	2014-03-23 20:39:48 UTC (rev 298)
+++ trunk/src/matlab.py	2014-05-23 12:41:47 UTC (rev 299)
@@ -1524,8 +1524,29 @@
     return (tf.num, tf.den)
 
 # Convert a continuous time system to a discrete time system
-def c2d(sysc, Ts, method):
-    # TODO: add docstring
+def c2d(sysc, Ts, method='zoh'):
+    '''
+    Return a discrete-time system
+
+    Parameters
+    ----------
+    sysc: Lti (StateSpace or TransferFunction), continuous
+        System to be converted
+
+    Ts: number
+        Sample time for the conversion
+
+    method: string, optional
+        Method to be applied, 
+        'zoh'        Zero-order hold on the inputs (default)
+        'foh'        First-order hold, currently not implemented
+        'impulse'    Impulse-invariant discretization, currently not implemented
+        'tustin'     Bilinear (Tustin) approximation, only SISO
+        'matched'    Matched pole-zero method, only SISO
+    '''
     #  Call the sample_system() function to do the work
-    return sample_system(sysc, Ts, method)
+    sysd = sample_system(sysc, Ts, method)
+    if isinstance(sysc, StateSpace) and not isinstance(sysd, StateSpace):
+        return _convertToStateSpace(sysd)
+    return sysd
 

Modified: trunk/src/statesp.py
===================================================================
--- trunk/src/statesp.py	2014-03-23 20:39:48 UTC (rev 298)
+++ trunk/src/statesp.py	2014-05-23 12:41:47 UTC (rev 299)
@@ -610,7 +610,7 @@
                 ssout[3][:sys.outputs, :states], 
                 ssout[4], sys.dt)
         except ImportError:
-            # TODO: do we want to squeeze first and check dimenations?
+            # TODO: do we want to squeeze first and check dimensions?
             # I think this will fail if num and den aren't 1-D after
             # the squeeze
             lti_sys = lti(squeeze(sys.num), squeeze(sys.den))

Modified: trunk/tests/discrete_test.py
===================================================================
--- trunk/tests/discrete_test.py	2014-03-23 20:39:48 UTC (rev 298)
+++ trunk/tests/discrete_test.py	2014-05-23 12:41:47 UTC (rev 299)
@@ -272,6 +272,10 @@
             self.assertEqual(sysd.dt, 1)
             # TODO: put in other generic checks
 
+        for sysc in (self.mimo_ss1, self.mimo_ss1c):
+            sysd = sample_system(sysc, 1, method='zoh')
+            self.assertEqual(sysd.dt, 1)
+
         # TODO: check results of converstion
 
         # Check errors

Modified: trunk/tests/matlab_test.py
===================================================================
--- trunk/tests/matlab_test.py	2014-03-23 20:39:48 UTC (rev 298)
+++ trunk/tests/matlab_test.py	2014-05-23 12:41:47 UTC (rev 299)
@@ -515,7 +515,26 @@
         np.testing.assert_array_almost_equal(hm.num[0][0], hr.num[0][0])
         np.testing.assert_array_almost_equal(hm.den[0][0], hr.den[0][0])
 
+    def testSS2cont(self):
+        sys = ss(
+            np.mat("-3 4 2; -1 -3 0; 2 5 3"),
+            np.mat("1 4 ; -3 -3; -2 1"),
+            np.mat("4 2 -3; 1 4 3"),
+            np.mat("-2 4; 0 1"))
+        sysd = c2d(sys, 0.1)
+        np.testing.assert_array_almost_equal(
+            np.mat(
+                """0.742840837331905  0.342242024293711  0.203124211149560;
+                  -0.074130792143890  0.724553295044645 -0.009143771143630;
+                   0.180264783290485  0.544385612448419  1.370501013067845"""),
+            sysd.A)
+        np.testing.assert_array_almost_equal(
+            np.mat(""" 0.012362066084719   0.301932197918268;
+                      -0.260952977031384  -0.274201791021713;
+                      -0.304617775734327   0.075182622718853"""), sysd.B)
+        
 
+
 #! TODO: not yet implemented
 #    def testMIMOtfdata(self):
 #        sisotf = ss2tf(self.siso_ss1)