improve tests and docs for delay-system inversion

JuliaControl · Dec 4, 2023 · bd74b9a · bd74b9a
1 parent 66e1475
commit bd74b9a
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Showing 2 changed files with 13 additions and 9 deletions.
diff --git a/lib/ControlSystemsBase/src/types/DelayLtiSystem.jl b/lib/ControlSystemsBase/src/types/DelayLtiSystem.jl
@@ -94,13 +94,16 @@ function +(sys::DelayLtiSystem{T1,S}, n::T2) where {T1,T2<:Number,S}
 end
 
 
+"""
+    /(G1, G2::DelayLtiSystem)
+
+Compute ``G_1 * G_2^{-1} where ``G_2`` is a DelayLtiSystem.
+Throws a SingularException if ``G_2`` is not invertible.
+"""
 function /(anything, sys::DelayLtiSystem)
-    if !all(iszero, sys.Tau)
-        ny,nu = size(sys)
-        ny == nu || error("The denominator system must be square")
-        return anything * feedback(I(nu), sys - I(nu))
-    end
-    /(anything, sys.P.P) # If all delays are zero, invert the inner system
+    ny,nu = size(sys)
+    ny == nu || error("The denominator system must be square")
+    return anything * feedback(I(nu), sys - I(nu))
 end
 
 for other_type in [:Number, :AbstractMatrix, :LTISystem]

diff --git a/lib/ControlSystemsBase/test/test_delayed_systems.jl b/lib/ControlSystemsBase/test/test_delayed_systems.jl
@@ -186,9 +186,10 @@ w = 10 .^ (-2:0.1:2)
 
 @test propertynames(delay(1.0)) == (:P, :Tau, :nu, :ny)
 
-@test_throws ErrorException 1/f2
-@test_throws ErrorException randn(2,2)/f2
-@test_throws ErrorException f2/f2
+@test_throws SingularException 1/f2
+@test_throws SingularException randn(2,2)/f2
+@test_throws SingularException f2/f2
+@test 1/(I(2)+f2) == feedback(I(2), f2)
 
 #FIXME: A lot more tests, including MIMO systems in particular