python-control · murrayrm · Jul 11, 2020 · Jun 26, 2020 · Jun 26, 2020 · Jun 27, 2020
diff --git a/control/config.py b/control/config.py
@@ -11,7 +11,7 @@
 
 __all__ = ['defaults', 'set_defaults', 'reset_defaults',
            'use_matlab_defaults', 'use_fbs_defaults',
-           'use_numpy_matrix']
+           'use_legacy_defaults', 'use_numpy_matrix']
 
 # Package level default values
 _control_defaults = {
@@ -53,6 +53,9 @@ def reset_defaults():
     from .rlocus import _rlocus_defaults
     defaults.update(_rlocus_defaults)
 
+    from .xferfcn import _xferfcn_defaults
+    defaults.update(_xferfcn_defaults)
+
     from .statesp import _statesp_defaults
     defaults.update(_statesp_defaults)
 
@@ -156,3 +159,16 @@ class and functions.  If flat is `False`, then matrices are
         warnings.warn("Return type numpy.matrix is soon to be deprecated.",
                       stacklevel=2)
     set_defaults('statesp', use_numpy_matrix=flag)
+
+def use_legacy_defaults(version):
+    """ Sets the defaults to whatever they were in a given release.
+
+    Parameters
+    ----------
+    version : string
+        version number of the defaults desired. Currently only supports `0.8.3`. 
+    """
+    if version == '0.8.3': 
+        use_numpy_matrix(True) # alternatively: set_defaults('statesp', use_numpy_matrix=True)
+    else:
+        raise ValueError('''version number not recognized. Possible values are: ['0.8.3']''') 
diff --git a/control/statesp.py b/control/statesp.py
@@ -71,7 +71,9 @@
 # Define module default parameter values
 _statesp_defaults = {
     'statesp.use_numpy_matrix': True,
-}
+    'statesp.default_dt': None,
+    'statesp.remove_useless_states': True, 
+    }
 
 
 def _ssmatrix(data, axis=1):
@@ -147,7 +149,8 @@ class StateSpace(LTI):
     Setting dt = 0 specifies a continuous system, while leaving dt = None
     means the system timebase is not specified.  If 'dt' is set to True, the
     system will be treated as a discrete time system with unspecified sampling
-    time.
+    time. The default value of 'dt' is None and can be changed by changing the 
+    value of ``control.config.defaults['statesp.default_dt']``.
 
     """
 
@@ -171,7 +174,7 @@ def __init__(self, *args, **kw):
         if len(args) == 4:
             # The user provided A, B, C, and D matrices.
             (A, B, C, D) = args
-            dt = None
+            dt = config.defaults['statesp.default_dt']
         elif len(args) == 5:
             # Discrete time system
             (A, B, C, D, dt) = args
@@ -187,12 +190,12 @@ def __init__(self, *args, **kw):
             try:
                 dt = args[0].dt
             except NameError:
-                dt = None
+                dt = config.defaults['statesp.default_dt']
         else:
             raise ValueError("Needs 1 or 4 arguments; received %i." % len(args))
 
         # Process keyword arguments
-        remove_useless = kw.get('remove_useless', True)
+        remove_useless = kw.get('remove_useless', config.defaults['statesp.remove_useless_states'])
 
         # Convert all matrices to standard form
         A = _ssmatrix(A)

diff --git a/control/tests/config_test.py b/control/tests/config_test.py
@@ -48,7 +48,7 @@ def test_get_param(self):
 
 
     def test_fbs_bode(self):
-        ct.use_fbs_defaults();
+        ct.use_fbs_defaults()
 
         # Generate a Bode plot
         plt.figure()
@@ -94,7 +94,7 @@ def test_fbs_bode(self):
         ct.reset_defaults()
 
     def test_matlab_bode(self):
-        ct.use_matlab_defaults();
+        ct.use_matlab_defaults()
 
         # Generate a Bode plot
         plt.figure()
@@ -211,6 +211,23 @@ def test_reset_defaults(self):
         self.assertEqual(
             ct.config.defaults['freqplot.feature_periphery_decades'], 1.0)
 
+    def test_legacy_defaults(self):
+        ct.use_legacy_defaults('0.8.3')
+        assert(isinstance(ct.ss(0,0,0,1).D, np.matrix))
+        ct.reset_defaults()
+        assert(isinstance(ct.ss(0,0,0,1).D, np.ndarray))
+
+    def test_change_default_dt(self):
+        ct.set_defaults('statesp', default_dt=0)
+        self.assertEqual(ct.ss(0,0,0,1).dt, 0)
+        ct.set_defaults('statesp', default_dt=None)
+        self.assertEqual(ct.ss(0,0,0,1).dt, None)
+        ct.set_defaults('xferfcn', default_dt=0)
+        self.assertEqual(ct.tf(1, 1).dt, 0)
+        ct.set_defaults('xferfcn', default_dt=None)
+        self.assertEqual(ct.tf(1, 1).dt, None)
+
+
     def tearDown(self):
         # Get rid of any figures that we created
         plt.close('all')

diff --git a/control/xferfcn.py b/control/xferfcn.py
@@ -63,10 +63,15 @@
 from itertools import chain
 from re import sub
 from .lti import LTI, timebaseEqual, timebase, isdtime
+from . import config
 
 __all__ = ['TransferFunction', 'tf', 'ss2tf', 'tfdata']
 
 
+# Define module default parameter values
+_xferfcn_defaults = {
+    'xferfcn.default_dt': None}
+
 class TransferFunction(LTI):
 
     """TransferFunction(num, den[, dt])
@@ -88,7 +93,9 @@ class TransferFunction(LTI):
     instance variable and setting it to something other than 'None'.  If 'dt'
     has a non-zero value, then it must match whenever two transfer functions
     are combined.  If 'dt' is set to True, the system will be treated as a
-    discrete time system with unspecified sampling time.
+    discrete time system with unspecified sampling time. The default value of 
+    'dt' is None and can be changed by changing the value of 
+    ``control.config.defaults['xferfcn.default_dt']``.
 
     The TransferFunction class defines two constants ``s`` and ``z`` that
     represent the differentiation and delay operators in continuous and
@@ -117,7 +124,7 @@ def __init__(self, *args):
         if len(args) == 2:
             # The user provided a numerator and a denominator.
             (num, den) = args
-            dt = None
+            dt = config.defaults['xferfcn.default_dt']
         elif len(args) == 3:
             # Discrete time transfer function
             (num, den, dt) = args
@@ -133,7 +140,7 @@ def __init__(self, *args):
             try:
                 dt = args[0].dt
             except NameError:   # pragma: no coverage
-                dt = None
+                dt = config.defaults['xferfcn.default_dt']
         else:
             raise ValueError("Needs 1, 2 or 3 arguments; received %i."
                              % len(args))

diff --git a/doc/conventions.rst b/doc/conventions.rst
@@ -98,7 +98,9 @@ the result will be a discrete time system with the sample time of the latter
 system.  For continuous time systems, the :func:`sample_system` function or
 the :meth:`StateSpace.sample` and :meth:`TransferFunction.sample` methods
 can be used to create a discrete time system from a continuous time system.
-See :ref:`utility-and-conversions`.
+See :ref:`utility-and-conversions`. The default value of 'dt' can be changed by
+changing the values of ``control.config.defaults['statesp.default_dt']`` and 
+``control.config.defaults['xferfcn.default_dt']``.
 
 Conversion between representations
 ----------------------------------
@@ -220,9 +222,15 @@ Selected variables that can be configured, along with their default values:
   * freqplot.feature_periphery_decade (1.0): How many decades to include in the
     frequency range on both sides of features (poles, zeros).
 
-  * statesp.use_numpy_matrix: set the return type for state space matrices to
+  * statesp.use_numpy_matrix (True): set the return type for state space matrices to
     `numpy.matrix` (verus numpy.ndarray)
 
+  * statesp.default_dt and xferfcn.default_dt (None): set the default value of dt when 
+  constructing new LTI systems
+
+  * statesp.remove_useless_states (True): remove states that have no effect on the 
+  input-output dynamics of the system 
+
 Additional parameter variables are documented in individual functions
 
 Functions that can be used to set standard configurations:
@@ -234,3 +242,4 @@ Functions that can be used to set standard configurations:
     use_fbs_defaults
     use_matlab_defaults
     use_numpy_matrix
+    use_legacy_defaults