Merge pull request #589 from bnavigator/drss-dt

Return a discrete time system with drss()

control/statesp.py

@@ -1434,11 +1434,11 @@ def _convert_to_statespace(sys, **kw):
 
 
 # TODO: add discrete time option
-def _rss_generate(states, inputs, outputs, type, strictly_proper=False):
+def _rss_generate(states, inputs, outputs, cdtype, strictly_proper=False):
     """Generate a random state space.
 
     This does the actual random state space generation expected from rss and
-    drss.  type is 'c' for continuous systems and 'd' for discrete systems.
+    drss.  cdtype is 'c' for continuous systems and 'd' for discrete systems.
 
     """
 
@@ -1465,6 +1465,8 @@ def _rss_generate(states, inputs, outputs, type, strictly_proper=False):
     if outputs < 1 or outputs % 1:
         raise ValueError("outputs must be a positive integer.  outputs = %g." %
                          outputs)
+    if cdtype not in ['c', 'd']:
+        raise ValueError("cdtype must be `c` or `d`")
 
     # Make some poles for A.  Preallocate a complex array.
     poles = zeros(states) + zeros(states) * 0.j
@@ -1484,16 +1486,16 @@ def _rss_generate(states, inputs, outputs, type, strictly_proper=False):
                 i += 2
         elif rand() < pReal or i == states - 1:
             # No-oscillation pole.
-            if type == 'c':
+            if cdtype == 'c':
                 poles[i] = -exp(randn()) + 0.j
-            elif type == 'd':
+            else:
                 poles[i] = 2. * rand() - 1.
             i += 1
         else:
             # Complex conjugate pair of oscillating poles.
-            if type == 'c':
+            if cdtype == 'c':
                 poles[i] = complex(-exp(randn()), 3. * exp(randn()))
-            elif type == 'd':
+            else:
                 mag = rand()
                 phase = 2. * math.pi * rand()
                 poles[i] = complex(mag * cos(phase), mag * sin(phase))
@@ -1546,7 +1548,11 @@ def _rss_generate(states, inputs, outputs, type, strictly_proper=False):
     C = C * Cmask
     D = D * Dmask if not strictly_proper else zeros(D.shape)
 
-    return StateSpace(A, B, C, D)
+    if cdtype == 'c':
+        ss_args = (A, B, C, D)
+    else:
+        ss_args = (A, B, C, D, True)
+    return StateSpace(*ss_args)
 
 
 # Convert a MIMO system to a SISO system
@@ -1825,15 +1831,14 @@ def rss(states=1, outputs=1, inputs=1, strictly_proper=False):
 
     Parameters
     ----------
-    states : integer
+    states : int
         Number of state variables
-    inputs : integer
+    inputs : int
         Number of system inputs
-    outputs : integer
+    outputs : int
         Number of system outputs
     strictly_proper : bool, optional
-        If set to 'True', returns a proper system (no direct term).  Default
-        value is 'False'.
+        If set to 'True', returns a proper system (no direct term).
 
     Returns
     -------
@@ -1867,12 +1872,15 @@ def drss(states=1, outputs=1, inputs=1, strictly_proper=False):
 
     Parameters
     ----------
-    states : integer
+    states : int
         Number of state variables
     inputs : integer
         Number of system inputs
-    outputs : integer
+    outputs : int
         Number of system outputs
+    strictly_proper: bool, optional
+        If set to 'True', returns a proper system (no direct term).
+
 
     Returns
     -------

control/tests/statesp_test.py

@@ -19,7 +19,7 @@
 from control.dtime import sample_system
 from control.lti import evalfr
 from control.statesp import (StateSpace, _convert_to_statespace, drss,
-                             rss, ss, tf2ss, _statesp_defaults)
+                             rss, ss, tf2ss, _statesp_defaults, _rss_generate)
 from control.tests.conftest import ismatarrayout, slycotonly
 from control.xferfcn import TransferFunction, ss2tf
 
@@ -855,6 +855,28 @@ def test_pole(self, states, outputs, inputs):
         for z in p:
             assert z.real < 0
 
+    @pytest.mark.parametrize('strictly_proper', [True, False])
+    def test_strictly_proper(self, strictly_proper):
+        """Test that the strictly_proper argument returns a correct D."""
+        for i in range(100):
+            # The probability that drss(..., strictly_proper=False) returns an
+            # all zero D 100 times in a row is 0.5**100 = 7.89e-31
+            sys = rss(1, 1, 1, strictly_proper=strictly_proper)
+            if np.all(sys.D == 0.) == strictly_proper:
+                break
+        assert np.all(sys.D == 0.) == strictly_proper
+
+    @pytest.mark.parametrize('par, errmatch',
+                             [((-1, 1, 1, 'c'), 'states must be'),
+                              ((1, -1, 1, 'c'), 'inputs must be'),
+                              ((1, 1, -1, 'c'), 'outputs must be'),
+                              ((1, 1, 1, 'x'), 'cdtype must be'),
+                              ])
+    def test_rss_invalid(self, par, errmatch):
+        """Test invalid inputs for rss() and drss()."""
+        with pytest.raises(ValueError, match=errmatch):
+            _rss_generate(*par)
+
 
 class TestDrss:
     """These are tests for the proper functionality of statesp.drss."""
@@ -873,6 +895,7 @@ def test_shape(self, states, outputs, inputs):
         assert sys.nstates == states
         assert sys.ninputs == inputs
         assert sys.noutputs == outputs
+        assert sys.dt is True
 
     @pytest.mark.parametrize('states', range(1, maxStates))
     @pytest.mark.parametrize('outputs', range(1, maxIO))
@@ -884,6 +907,17 @@ def test_pole(self, states, outputs, inputs):
         for z in p:
             assert abs(z) < 1
 
+    @pytest.mark.parametrize('strictly_proper', [True, False])
+    def test_strictly_proper(self, strictly_proper):
+        """Test that the strictly_proper argument returns a correct D."""
+        for i in range(100):
+            # The probability that drss(..., strictly_proper=False) returns an
+            # all zero D 100 times in a row is 0.5**100 = 7.89e-31
+            sys = drss(1, 1, 1, strictly_proper=strictly_proper)
+            if np.all(sys.D == 0.) == strictly_proper:
+                break
+        assert np.all(sys.D == 0.) == strictly_proper
+
 
 class TestLTIConverter:
     """Test returnScipySignalLTI method"""