Fix #192 (#194)

Author: dlfivefifty

Project.toml

@@ -1,7 +1,7 @@
 name = "ClassicalOrthogonalPolynomials"
 uuid = "b30e2e7b-c4ee-47da-9d5f-2c5c27239acd"
 authors = ["Sheehan Olver <[email protected]>"]
-version = "0.13.2"
+version = "0.13.3"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"

src/clenshaw.jl

@@ -211,7 +211,7 @@ function clenshaw(c::AbstractVector, A::AbstractVector, B::AbstractVector, C::Ab
     m = size(X,1)
     m == size(X,2) || throw(DimensionMismatch("X must be square"))
     m == length(f) || throw(DimensionMismatch("Dimensions must match"))
-    N == 0 && return zero(T)
+    N == 0 && return [zero(T)]
     bn2 = zeros(T,m)
     bn1 = Vector{T}(undef,m)
     bn1 .= c[N] .* f

test/test_chebyshev.jl

@@ -561,6 +561,14 @@ import BandedMatrices: isbanded
         f = x -> abs(x) ≤ 1 ? 1 : "hi"
         @test T \ f.(axes(T,1)) ≈ [1; zeros(∞)]
     end
+
+    @testset "empty Clenshaw (#192)" begin
+        a = (x,α) -> α*(1-x^2)
+        T = ChebyshevT()
+        x = axes(T, 1)
+        A = T \ (a.(x, 0.) .* T)
+        @test iszero(A[1,1])
+    end
 end
 
 struct QuadraticMap{T} <: Map{T} end