suggested changes in docstrings

sawyerbfuller · sawyerbfuller · commit 4ad33db513b1 · 2020-08-17T11:13:06.000-07:00
diff --git a/control/frdata.py b/control/frdata.py
@@ -365,8 +365,8 @@ def eval(self, omega, squeeze=True):
             elements = np.isin(self.omega, omega) # binary array
             if sum(elements) < len(omega_array):
                 raise ValueError(
-                    '''not all frequencies omega are in frequency list of FRD 
-                    system. Try an interpolating FRD for additional points.''')
+                    "not all frequencies omega are in frequency list of FRD "
+                    "system. Try an interpolating FRD for additional points.")
             else:
                 out = self.fresp[:, :, elements]
         else:
diff --git a/control/margins.py b/control/margins.py
@@ -56,6 +56,8 @@
 from . import xferfcn
 from .lti import issiso
 from . import frdata
+from .exception import ControlMIMONotImplemented
+
 
 __all__ = ['stability_margins', 'phase_crossover_frequencies', 'margin']
 
@@ -155,7 +157,7 @@ def stability_margins(sysdata, returnall=False, epsw=0.0):
 
         # check for siso
         if not issiso(sys):
-            raise ValueError("Can only do margins for SISO system")
+            raise ControlMIMONotImplemented()
 
         # real and imaginary part polynomials in omega:
         rnum, inum = _polyimsplit(sys.num[0][0])
@@ -297,7 +299,7 @@ def phase_crossover_frequencies(sys):
     """
 
     if not sys.issiso(): 
-        raise ValueError("MIMO systems not yet implemented.")
+        raise ControlMIMONotImplemented()
     # Convert to a transfer function
     tf = xferfcn._convert_to_transfer_function(sys)
     num = tf.num[0][0]
diff --git a/control/rlocus.py b/control/rlocus.py
@@ -472,7 +472,7 @@ def _systopoly1d(sys):
         sys = _convert_to_transfer_function(sys)
 
         # Make sure we have a SISO system
-        if (sys.inputs > 1 or sys.outputs > 1):
+        if not sys.issiso():
             raise ControlMIMONotImplemented()
 
         # Start by extracting the numerator and denominator from system object
