add method for computing the determinant of a system

Author: baggepinnen

lib/ControlSystemsBase/src/matrix_comps.jl

@@ -1019,4 +1019,13 @@ end
 
 function observer_filter(sys::AbstractStateSpace{Continuous}, K::AbstractMatrix; kwargs...)
     observer_predictor(sys, K; kwargs...)
-end
+end
+
+function LinearAlgebra.det(sys::LTISystem)
+    sys = deepcopy(sys)
+    arrayofsys = getindex.(Ref(sys), 1:sys.ny, (1:sys.nu)')
+    if sys isa AbstractStateSpace
+        @. arrayofsys = sminreal(arrayofsys)
+    end
+    LinearAlgebra.det_bareiss!(arrayofsys)
+end

lib/ControlSystemsBase/src/types/StateSpace.jl

@@ -265,6 +265,10 @@ Base.zero(sys::AbstractStateSpace) = basetype(sys)(zero(sys.D), sys.timeevol)
 Base.zero(::Type{StateSpace{Continuous, F}}) where {F} = ss([zero(F)], Continuous())
 Base.zero(::Type{StateSpace{D, F}}) where {D<:Discrete, F} = ss([zero(F)], undef_sampletime(D))
 
+# one is a multiplicative identity, which can be set to the one of the element type. This is different from oneunit which should be of the same type.
+Base.one(::Type{StateSpace{TE, T}}) where {TE, T} = Base.one(T)
+
+
 function +(s1::ST, s2::ST) where {ST <: AbstractStateSpace}
     #Ensure systems have same dimensions
     if size(s1) != size(s2)

lib/ControlSystemsBase/test/test_matrix_comps.jl

@@ -11,6 +11,12 @@ sysr, G = balreal(sys)
 @test gram(sysr, :o) ≈ diagm(G)
 @test sort(poles(sysr), by=real) ≈ sort(poles(sys), by=real)
 
+@testset "det" begin
+    detsys = det(sys)
+    w = 0.1
+    @test freqresp(detsys, w)[1] ≈ det(freqresp(sys, w))
+end
+
 sysb,T = ControlSystemsBase.balance_statespace(sys)
 @test similarity_transform(sysb, T) ≈ sys
 Ab,Bb,Cb,T = ControlSystemsBase.balance_statespace(A,B,C)