[python-control-discuss] SF.net python-control commit:[289] trunk

[<mur...@us...>]

Revision: 289
          http://sourceforge.net/p/python-control/code/289
Author:   murrayrm
Date:     2013-07-15 04:39:59 +0000 (Mon, 15 Jul 2013)
Log Message:
-----------
Updated sample_system() function to check for proper version of SciPy.  If cont2discrete is not avialable (requires scipy 0.10.0+), generate a warning. 

Modified Paths:
--------------
    trunk/ChangeLog
    trunk/src/dtime.py

Modified: trunk/ChangeLog
===================================================================
--- trunk/ChangeLog	2013-06-25 06:07:45 UTC (rev 288)
+++ trunk/ChangeLog	2013-07-15 04:39:59 UTC (rev 289)
@@ -1,3 +1,9 @@
+2013-07-14  Richard Murray  <murray@altura-2.local>
+
+	* src/dtime.py (sample_system): added check to make sure
+	cont2discrete is available in scipy.signal
+	(sample_system): added docstring
+
 2013-06-24  Richard Murray  <murray@altura-2.local>
 
 	* tests/minreal_test.py (TestMinreal.testMinrealBrute),

Modified: trunk/src/dtime.py
===================================================================
--- trunk/src/dtime.py	2013-06-25 06:07:45 UTC (rev 288)
+++ trunk/src/dtime.py	2013-07-15 04:39:59 UTC (rev 289)
@@ -47,7 +47,7 @@
 
 """
 
-from scipy.signal import zpk2tf, tf2zpk, cont2discrete
+from scipy.signal import zpk2tf, tf2zpk
 import numpy as np
 from cmath import exp
 from warnings import warn
@@ -57,8 +57,39 @@
 
 # Sample a continuous time system
 def sample_system(sysc, Ts, method='matched'):
-    # TODO: add docstring
+    """Convert a continuous time system to discrete time
 
+    Creates a discrete time system from a continuous time system by
+    sampling.  Multiple methods of conversion are supported.
+
+    Parameters
+    ----------
+    sysc : linsys
+        Continuous time system to be converted
+    Ts : real
+        Sampling period
+    method : string
+        Method to use for conversion: 'matched' (default), 'tustin', 'zoh'
+
+    Returns
+    -------
+    sysd : linsys
+        Discrete time system, with sampling rate Ts
+
+    Notes
+    -----
+    1. The conversion methods 'tustin' and 'zoh' require the
+       cont2discrete() function, including in SciPy 0.10.0 and above.
+
+    2. Additional methods 'foh' and 'impulse' are planned for future
+       implementation.
+
+    Examples
+    --------
+    >>> sysc = TransferFunction([1], [1, 2, 1])
+    >>> sysd = sample_system(sysc, 1, method='matched')
+    """
+
     # Make sure we have a continuous time system
     if not isctime(sysc):
         raise ValueError("First argument must be continuous time system")
@@ -77,14 +108,22 @@
         sysd = _c2dmatched(sysc, Ts)
 
     elif method == 'tustin':
-        sys = [sysc.num[0][0], sysc.den[0][0]]
-        scipySysD = cont2discrete(sys, Ts, method='bilinear')
-        sysd = TransferFunction(scipySysD[0][0], scipySysD[1], dt)
-
+        try:
+            from scipy.signal import cont2discrete
+            sys = [sysc.num[0][0], sysc.den[0][0]]
+            scipySysD = cont2discrete(sys, Ts, method='bilinear')
+            sysd = TransferFunction(scipySysD[0][0], scipySysD[1], dt)
+        except ImportError:
+            raise TypeError("cont2discrete not found in scipy.signal; upgrade to v0.10.0+")
+        
     elif method == 'zoh':
-        sys = [sysc.num[0][0], sysc.den[0][0]]
-        scipySysD = cont2discrete(sys, Ts, method='zoh')
-        sysd = TransferFunction(scipySysD[0][0],scipySysD[1], dt)
+        try:
+            from scipy.signal import cont2discrete
+            sys = [sysc.num[0][0], sysc.den[0][0]]
+            scipySysD = cont2discrete(sys, Ts, method='zoh')
+            sysd = TransferFunction(scipySysD[0][0],scipySysD[1], dt)
+        except ImportError:
+            raise TypeError("cont2discrete not found in scipy.signal; upgrade to v0.10.0+")
 
     elif method == 'foh' or method == 'impulse':
         raise ValueError("Method not developed yet")