Fix grammar in doc string.

Mark · Mark · commit 7e79c822d069 · 2022-06-13T15:36:56.000-05:00
diff --git a/control/passivity.py b/control/passivity.py
@@ -16,7 +16,7 @@ def is_passive(sys):
     Indicates if a linear time invarient system is passive
 
     Constructs a linear matrix inequality and a feasibility optimization
-    such that is a solution exists, the system is passive.
+    such that if a solution exists, the system is passive.
 
     The source for the algorithm is: 
     McCourt, Michael J., and Panos J. Antsaklis. 
