close #598 (#599)

Author: jverzani

Project.toml

@@ -2,7 +2,7 @@ name = "Polynomials"
 uuid = "f27b6e38-b328-58d1-80ce-0feddd5e7a45"
 license = "MIT"
 author = "JuliaMath"
-version = "4.0.17"
+version = "4.0.18"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/polynomials/ngcd.jl

@@ -12,6 +12,13 @@ function ngcd(p::P, q::Q,
               args...;
               kwargs...) where {T,X,P<:StandardBasisPolynomial{T,X},
                                 S,Y,Q<:StandardBasisPolynomial{S,Y}}
+
+    # easy cases
+    degree(p) < 0  && return (u=q,      v=p, w=one(q),  θ=NaN, κ=NaN)
+    degree(p) == 0 && return (u=one(q), v=p, w=q,       θ=NaN, κ=NaN)
+    degree(q) < 0  && return (u=one(q), v=p, w=zero(q), θ=NaN, κ=NaN)
+    degree(q) == 0 && return (u=one(p), v=p, w=q,       Θ=NaN, κ=NaN)
+
     if (degree(q) > degree(p))
         u,w,v,Θ,κ =  ngcd(q,p,args...; kwargs...)
         return (u=u,v=v,w=w, Θ=Θ, κ=κ)
@@ -21,14 +28,12 @@ function ngcd(p::P, q::Q,
         return ngcd(q, b, args...; λ=100,  kwargs...)
     end
 
-    # easy cases
-    degree(p) < 0  && return (u=q,      v=p, w=one(q),  θ=NaN, κ=NaN)
-    degree(p) == 0 && return (u=one(q), v=p, w=q,       θ=NaN, κ=NaN)
-    degree(q) < 0  && return (u=one(q), v=p, w=zero(q), θ=NaN, κ=NaN)
-    degree(q) == 0 && return (u=one(p), v=p, w=q,       Θ=NaN, κ=NaN)
+    # other easy cases
     p ≈ q          && return (u=p,v=one(p),  w=one(p),  θ=NaN, κ=NaN)
     Polynomials.assert_same_variable(p,q)
 
+
+
     R = promote_type(float(T))
     𝑷 = Polynomials.constructorof(P){R,X}
 

test/StandardBasis.jl

@@ -1558,6 +1558,15 @@ end
             @test out.u == x^k
         end
     end
+
+    # issue #598 ultimately ngcd issue not checking 0 polynomial earlier
+    x = Polynomial([0,1])
+    A = (1.0 + 2.0*x^2) // (1.0 + 2.0*x^2)
+    B = (0.0) // (1.0 + 2.0*x^2)
+    C = (3.0*x) // (1.0 + 2.0*x^2)
+    D = (1.0 + 2.0*x^2) // (1.0 + 2.0*x^2)
+    ab,cd = [A B], [C D]
+    @test [A B; C D] == [ab; cd]
 end
 
 @testset "Showing" begin