updated per @slivingston review comments

Author: murrayrm

control/nlsys.py

@@ -93,7 +93,7 @@ class NonlinearIOSystem(InputOutputSystem):
         generic name <sys[id]> is generated with a unique integer id.
 
     params : dict, optional
-       Parameter values for the system.  Passed to the evaluation functions
+        Parameter values for the system.  Passed to the evaluation functions
         for the system as default values, overriding internal defaults.
 
     See Also
@@ -1671,7 +1671,7 @@ def ivp_rhs(t, x):
         success=soln.success, message=message)
 
 
-class OperatingPoint(object):
+class OperatingPoint():
     """A class for representing the operating point of a nonlinear I/O system.
 
     The ``OperatingPoint`` class stores the operating point of a nonlinear
@@ -1693,18 +1693,18 @@ class OperatingPoint(object):
 
     """
     def __init__(
-            self, states, inputs=None, outputs=None, result=None,
+            self, states, inputs, outputs=None, result=None,
             return_outputs=False, return_result=False):
         self.states = states
         self.inputs = inputs
 
         if outputs is None and return_outputs and not return_result:
-            raise SystemError("return_outputs specified by no y0 value")
+            raise ValueError("return_outputs specified but no outputs value")
         self.outputs = outputs
         self.return_outputs = return_outputs
 
         if result is None and return_result:
-            raise SystemError("return_result specified by no result value")
+            raise ValueError("return_result specified but no result value")
         self.result = result
         self.return_result = return_result
 
@@ -1799,7 +1799,7 @@ def find_operating_point(
         values will be ignored in solving for an operating point.  State
         indices can be listed in any order.  By default, all updates will be
         fixed at `dx0` in searching for an operating point.
-    root_method : str, optonal
+    root_method : str, optional
         Method to find the operating point.  If specified, this parameter
         is passed to the :func:`scipy.optimize.root` function.
     root_kwargs : dict, optional

control/tests/iosys_test.py

@@ -2089,7 +2089,6 @@ def test_find_eqpt(x0, ix, u0, iu, y0, iy, dx0, idx, dt, x_expect, u_expect):
 
 
 # Test out new operating point version of find_eqpt
-# TODO: add return_)y tests
 def test_find_operating_point():
     dt = 1
     sys = ct.NonlinearIOSystem(
@@ -2148,7 +2147,7 @@ def test_operating_point():
     np.testing.assert_allclose(linsys_orig.C, linsys_oppt.C)
     np.testing.assert_allclose(linsys_orig.D, linsys_oppt.D)
 
-    # Call find_operating point with method and keyword arguments
+    # Call find_operating_point with method and keyword arguments
     op_point = ct.find_operating_point(
         sys, 0, 0, root_method='lm', root_kwargs={'tol': 1e-6})
 

examples/cruise-control.py

@@ -349,7 +349,7 @@ def cruise_plot(sys, t, y, label=None, t_hill=None, vref=20, antiwindup=False,
 # and u given the gear, slope, and desired output velocity)
 X0, U0, Y0 = ct.find_operating_point(
     cruise_pi, [vref[0], 0], [vref[0], gear[0], theta0[0]],
-    y0=[0, vref[0]], iu=[1, 2], iy=[1], return_y=True)
+    y0=[0, vref[0]], iu=[1, 2], iy=[1], return_outputs=True)
 
 # Now simulate the effect of a hill at t = 5 seconds
 plt.figure()

examples/cruise.ipynb

@@ -804,7 +804,7 @@
     "# Compute the equilibrium throttle setting for the desired speed\n",
     "X0, U0, Y0 = ct.find_eqpt(\n",
     "    cruise_pi, [vref[0], 0], [vref[0], gear[0], theta0[0]],\n",
-    "    y0=[0, vref[0]], iu=[1, 2], iy=[1], return_y=True)\n",
+    "    y0=[0, vref[0]], iu=[1, 2], iy=[1], return_outputs=True)\n",
     "\n",
     "# Now simulate the effect of a hill at t = 5 seconds\n",
     "plt.figure()\n",