only call np.delete with actual removal (#430)

bnavigator · web-flow · commit c7c7b4754dcb · 2020-07-10T19:27:07.000-07:00
diff --git a/control/iosys.py b/control/iosys.py
@@ -1645,8 +1645,10 @@ def rootfun(z):
         # and were processed above.
 
         # Get the states and inputs that were not listed as fixed
-        state_vars = np.delete(np.array(range(nstates)), ix)
-        input_vars = np.delete(np.array(range(ninputs)), iu)
+        state_vars = (range(nstates) if not len(ix)
+                      else np.delete(np.array(range(nstates)), ix))
+        input_vars = (range(ninputs) if not len(iu)
+                      else np.delete(np.array(range(ninputs)), iu))
 
         # Set the outputs and derivs that will serve as constraints
         output_vars = np.array(iy)
