better error messages for failed inversion

JuliaControl · Dec 6, 2023 · 2b41c29 · 2b41c29
1 parent b51adf7
commit 2b41c29
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/lib/ControlSystemsBase/src/types/StateSpace.jl b/lib/ControlSystemsBase/src/types/StateSpace.jl
@@ -431,10 +431,11 @@ end
 function /(n::Number, sys::ST) where ST <: AbstractStateSpace
     # Ensure s.D is invertible
     A, B, C, D = ssdata(sys)
+    LinearAlgebra.checksquare(D) || error("The inverted system must have the same number of inputs and outputs")
     Dinv = try
         inv(D)
     catch
-        error("D isn't invertible")
+        error("D isn't invertible. If you are trying to form a quotient between two systems `N(s) / D(s)` where the quotient is proper but the inverse of `D(s)` isn't, consider calling `N / D` instead of `N * inv(D)")
     end
     return basetype(ST)(A - B*Dinv*C, B*Dinv, -n*Dinv*C, n*Dinv, sys.timeevol)
 end