Move complexroots (#332)

Author: jishnub

Project.toml

@@ -1,6 +1,6 @@
 name = "ApproxFunBase"
 uuid = "fbd15aa5-315a-5a7d-a8a4-24992e37be05"
-version = "0.7.53"
+version = "0.7.54"
 
 [deps]
 AbstractFFTs = "621f4979-c628-5d54-868e-fcf4e3e8185c"

src/specialfunctions.jl

@@ -587,8 +587,30 @@ end
 extrema(f::Fun{PiecewiseSpace{<:Any,<:UnionDomain,<:Real},<:Real}) =
     mapreduce(extrema,(x,y)->extrema([x...;y...]),components(f))
 
+function companion_matrix(c::Vector{T}) where T
+    n=length(c)-1
+
+    A=zeros(T,n,n)
+
+    for k=1:n
+        A[k,end]=-c[k]/c[end]
+    end
+
+    for k=2:n
+        A[k,k-1]=one(T)
+    end
+
+    return A
+end
+
 function complexroots end
 
+complexroots(cfs::Vector{<:Union{Float64,ComplexF64}}) =
+    hesseneigvals(companion_matrix(chop(cfs,10eps())))
+
+complexroots(neg::Vector, pos::Vector) =
+    complexroots([reverse(chop(neg,10eps()), dims=1); pos])
+
 function roots(f::Fun{<:PiecewiseSpace})
     rts=mapreduce(roots,vcat,components(f))
     k=1

test/runtests.jl

@@ -431,6 +431,13 @@ end
         λ2 = eigvals(B)
         @test λ1 ≈ λ2
     end
+
+    @testset "complexroots" begin
+        cfs = [1.0, 1.0]
+        r = complexroots(cfs)
+        @test r == [-1.0]
+        @test complexroots([0.0], cfs) == [-1.0]
+    end
 end
 
 @testset "Special functions" begin