bugfix: Fixes #253, misplaced 2 in *(Number, DelayLTISystem).

Author: olof3

src/types/DelayLtiSystem.jl

@@ -72,7 +72,7 @@ Base.convert(::Type{V}, sys::DelayLtiSystem)  where {T, V<:DelayLtiSystem{T}} =
 
 function *(sys::DelayLtiSystem, n::Number)
     new_C = [sys.P.C1*n; sys.P.C2]
-    new_D = [sys.P.D11*n sys.P.D12; sys.P.D21*n sys.P.D22]
+    new_D = [sys.P.D11*n sys.P.D12*n; sys.P.D21 sys.P.D22]
     return DelayLtiSystem(StateSpace(sys.P.A, sys.P.B, new_C, new_D, sys.P.Ts), sys.Tau)
 end
 *(n::Number, sys::DelayLtiSystem) = *(sys, n)

test/test_delayed_systems.jl

@@ -31,6 +31,9 @@ P2_fr = (im*ω .+ 1) ./ (im*ω .+ 2)
 # Substraction
 @test freqresp(P1 - delay(1), ω)[:] ≈ P1_fr .- exp.(-im*ω)
 
+## Multiplication by scalar
+@test freqresp(2*delay(1), ω)[:] ≈ 2*exp.(-im*ω)
+@test freqresp(2*(P1*delay(1)), ω)[:] ≈ 2*P1_fr.*exp.(-im*ω)
 
 ## Multiplication
 @test freqresp(P1 * delay(1), ω)[:] ≈ P1_fr .* exp.(-im*ω) rtol=1e-15