update userguide examples (copyedits + additional narrative)

Author: murrayrm

control/dtime.py

@@ -63,7 +63,8 @@ def sample_system(sysc, Ts, method='zoh', alpha=None, prewarp_frequency=None,
     Notes
     -----
     See `StateSpace.sample` or `TransferFunction.sample` for further
-    details.
+    details on implementation for state space and transfer function
+    systems, including available methods.
 
     Examples
     --------

control/stochsys.py

@@ -468,8 +468,8 @@ def create_estimator_iosystem(
 
     # Set the output matrices
     if C is not None:
-        # Make sure that we have the full system output
-        if not np.array_equal(sys.C, np.eye(sys.nstates)):
+        # Make sure we have full system output (allowing for numerical errors)
+        if not np.allclose(sys.C, np.eye(sys.nstates)):
             raise ValueError("System output must be full state")
 
         # Make sure that the output matches the size of RN