Update control/frdata.py

sawyerbfuller · bnavigator · web-flow · commit 8486b7a46cb4 · 2020-08-17T10:49:14.000-07:00
Co-authored-by: Ben Greiner &lt;code@bnavigator.de&gt;
diff --git a/control/frdata.py b/control/frdata.py
@@ -391,12 +391,24 @@ def __call__(self, s, squeeze=True):
         transfer function.  For a MIMO transfer fuction, returns a
         matrix of values.
         
-        Raises an error if s is not purely imaginary. 
-        
+        Parameters
+        ----------
+        s : scalar or array_like
+            Complex frequencies
         squeeze: bool, optional (default=True)
             If True and sys is single input, single output (SISO), return a 
             1D array or scalar depending on omega's length.
 
+        Returns
+        -------
+        ndarray or scalar
+            Frequency response
+
+        Raises
+        ------
+        ValueError
+            If `s` is not purely imaginary. 
+
         """
         if any(abs(np.array(s, ndmin=1).real) > 0):
             raise ValueError("__call__: FRD systems can only accept"
