Merge pull request #657 from JuliaControl/ss2tftypestab

fix type stability in ss2tf conversion

Author: baggepinnen

src/types/conversion.jl

@@ -300,10 +300,9 @@ end
 
 # TODO: Could perhaps be made more accurate. See: An accurate and efficient
 # algorithm for the computation of the # characteristic polynomial of a general square matrix.
-function charpoly(A::AbstractMatrix{<:Number})
-    Λ = eigvalsnosort(A)
-
-    return prod(roots2poly_factors(Λ)) # Compute the polynomial factors directly?
+function charpoly(A::AbstractMatrix{T}) where T
+    Λ::Vector{T} = eigvalsnosort(A)
+    return prod(roots2poly_factors(Λ))::Polynomial{T,:x} # Compute the polynomial factors directly?
 end
 function charpoly(A::AbstractMatrix{<:Real})
     Λ = eigvalsnosort(A)

src/utilities.jl

@@ -54,12 +54,12 @@ printpolyfun(var) = (io, p, mimetype = MIME"text/plain"()) -> Polynomials.printp
 # returned by LAPACK routines for eigenvalues.
 function roots2real_poly_factors(roots::Vector{cT}) where cT <: Number
     T = real(cT)
-    poly_factors = Vector{Polynomial{T}}()
+    poly_factors = Vector{Polynomial{T,:x}}()
     for k=1:length(roots)
         r = roots[k]
 
         if isreal(r)
-            push!(poly_factors,Polynomial{T}([-real(r),1]))
+            push!(poly_factors,Polynomial{T,:x}([-real(r),1]))
         else
             if imag(r) < 0 # This roots was handled in the previous iteration # TODO: Fix better error handling
                 continue
@@ -69,7 +69,7 @@ function roots2real_poly_factors(roots::Vector{cT}) where cT <: Number
                 throw(ArgumentError("Found pole without matching conjugate."))
             end
 
-            push!(poly_factors,Polynomial{T}([real(r)^2+imag(r)^2, -2*real(r), 1]))
+            push!(poly_factors,Polynomial{T,:x}([real(r)^2+imag(r)^2, -2*real(r), 1]))
             # k += 1 # Skip one iteration in the loop
         end
     end
@@ -78,7 +78,7 @@ function roots2real_poly_factors(roots::Vector{cT}) where cT <: Number
 end
 # This function should hande both Complex as well as symbolic types
 function roots2poly_factors(roots::Vector{T}) where T <: Number
-    return Polynomial{T}[Polynomial{T}([-r, 1]) for r in roots]
+    return Polynomial{T,:x}[Polynomial{T,:x}([-r, 1]) for r in roots]
 end
 
 

test/test_conversion.jl

@@ -1,5 +1,11 @@
 @testset "test_conversion" begin
 
+A = randn(3,3)
+@inferred ControlSystems.charpoly(A)
+
+A = randn(ComplexF64,3,3)
+@inferred ControlSystems.charpoly(A)
+
 G = tf(1.0,[1,1])
 H = zpk([0.0], [1.0], 1.0)
 @inferred ControlSystems.siso_tf_to_ss(Float64, G.matrix[1,1])