Fix variable order in partial derivatives (#207)

Author: dlfivefifty

Project.toml

@@ -1,6 +1,6 @@
 name = "MultivariateOrthogonalPolynomials"
 uuid = "4f6956fd-4f93-5457-9149-7bfc4b2ce06d"
-version = "0.9.1"
+version = "0.9.2"
 
 [deps]
 ArrayLayouts = "4c555306-a7a7-4459-81d9-ec55ddd5c99a"

src/rect.jl

@@ -53,8 +53,8 @@ function jacobimatrix(::Val{2}, P::RectPolynomial)
     KronTrav(Y, Eye{eltype(Y)}(∞))
 end
 function diff(P::KronPolynomial{N}, order::NTuple{N,Int}; dims...) where N
-    diffs = diff.(P.args, order)
-    RectPolynomial(basis.(diffs)...) * KronTrav(coefficients.(diffs)...)
+    diffs = map(diff, P.args, order)
+    RectPolynomial(map(basis, diffs)...) * KronTrav(reverse(map(coefficients, diffs))...)
 end
 
 
@@ -164,7 +164,7 @@ end
 
 ## sum
 
-function Base._sum(P::RectPolynomial, dims)
+function Base._sum(P::RectPolynomial, dims::Int)
     @assert dims == 1
     KronTrav(sum.(P.args; dims=1)...)
 end

test/test_rect.jl

@@ -155,6 +155,21 @@ using Base: oneto
         @test sum(f) ≈ 10.546408460894801 # empirical
     end
 
+    @testset "diff" begin
+        P = RectPolynomial(Legendre(),Legendre())
+        f = expand(P, splat((x,y) -> 1))
+        @test diff(f,(1,0))[SVector(0.1,0.2)] == diff(f,(0,1))[SVector(0.1,0.2)] == 0.0
+        f = expand(P, splat((x,y) -> x))
+        @test diff(f,(1,0))[SVector(0.1,0.2)] == 1.0
+        @test diff(f,(0,1))[SVector(0.1,0.2)] == 0.0
+        f = expand(P, splat((x,y) -> cos(x*exp(y))))
+        @test diff(f,(1,0))[SVector(0.1,0.2)] ≈ -sin(0.1*exp(0.2))*exp(0.2)
+        @test diff(f,(0,1))[SVector(0.1,0.2)] ≈ -0.1*sin(0.1*exp(0.2))*exp(0.2)
+        @test diff(f,(2,0))[SVector(0.1,0.2)] ≈ -cos(0.1*exp(0.2))*exp(0.4)
+        @test diff(f,(1,1))[SVector(0.1,0.2)] ≈ -sin(0.1*exp(0.2))*exp(0.2) - 0.1*cos(0.1*exp(0.2))*exp(0.4)
+        @test diff(f,(0,2))[SVector(0.1,0.2)] ≈ -0.1*sin(0.1*exp(0.2))*exp(0.2) - 0.1^2*cos(0.1*exp(0.2))*exp(0.4)
+    end
+
     @testset "KronTrav bug" begin
         W = Weighted(Ultraspherical(3/2))
         D² = diff(W)'diff(W)