Simplify rule according to feedback in #531 (#549)

Co-authored-by: David Widmann <devmotion@users.noreply.github.com>

Author: simsurace

src/chainrules.jl

@@ -111,10 +111,9 @@ end
 
 function ChainRulesCore.rrule(s::Sinus, x::AbstractVector, y::AbstractVector)
     d = x - y
-    sind = sinpi.(d)
-    abs2_sind_r = abs2.(sind) ./ s.r .^ 2
+    abs2_sind_r = (sinpi.(d) ./ s.r) .^ 2
     val = sum(abs2_sind_r)
-    gradx = twoπ .* cospi.(d) .* sind ./ s.r .^ 2
+    gradx = π .* sinpi.(2 .* d) ./ s.r .^ 2
     function evaluate_pullback(Δ::Any)
         r̄ = -2Δ .* abs2_sind_r ./ s.r
         s̄ = ChainRulesCore.Tangent{typeof(s)}(; r=r̄)
@@ -136,7 +135,7 @@ function ChainRulesCore.rrule(
             for j in 1:n, i in 1:n
                 xi = view(x, i, :)
                 xj = view(x, j, :)
-                ds = twoπ .* Δ[i, j] .* sinpi.(xi .- xj) .* cospi.(xi .- xj) ./ d.r .^ 2
+                ds = π .* Δ[i, j] .* sinpi.(2 .* (xi .- xj)) ./ d.r .^ 2
                 r̄ .-= 2 .* Δ[i, j] .* sinpi.(xi .- xj) .^ 2 ./ d.r .^ 3
                 x̄[i, :] += ds
                 x̄[j, :] -= ds
@@ -147,8 +146,8 @@ function ChainRulesCore.rrule(
                 xj = view(x, :, j)
                 ds = twoπ .* Δ[i, j] .* sinpi.(xi .- xj) .* cospi.(xi .- xj) ./ d.r .^ 2
                 r̄ .-= 2 .* Δ[i, j] .* sinpi.(xi .- xj) .^ 2 ./ d.r .^ 3
-                x̄[:, i] += ds
-                x̄[:, j] -= ds
+                x̄[:, i] .+= ds
+                x̄[:, j] .-= ds
             end
         end
         d̄ = ChainRulesCore.Tangent{typeof(d)}(; r=r̄)
@@ -173,19 +172,19 @@ function ChainRulesCore.rrule(
             for j in 1:m, i in 1:n
                 xi = view(x, i, :)
                 yj = view(y, j, :)
-                ds = twoπ .* Δ[i, j] .* sinpi.(xi .- yj) .* cospi.(xi .- yj) ./ d.r .^ 2
+                ds = π .* Δ[i, j] .* sinpi.(2 .* (xi .- yj)) ./ d.r .^ 2
                 r̄ .-= 2 .* Δ[i, j] .* sinpi.(xi .- yj) .^ 2 ./ d.r .^ 3
-                x̄[i, :] += ds
-                ȳ[j, :] -= ds
+                x̄[i, :] .+= ds
+                ȳ[j, :] .-= ds
             end
         elseif dims == 2
             for j in 1:m, i in 1:n
                 xi = view(x, :, i)
                 yj = view(y, :, j)
-                ds = twoπ .* Δ[i, j] .* sinpi.(xi .- yj) .* cospi.(xi .- yj) ./ d.r .^ 2
+                ds = π .* Δ[i, j] .* sinpi.(2 .* (xi .- yj)) ./ d.r .^ 2
                 r̄ .-= 2 .* Δ[i, j] .* sinpi.(xi .- yj) .^ 2 ./ d.r .^ 3
-                x̄[:, i] += ds
-                ȳ[:, j] -= ds
+                x̄[:, i] .+= ds
+                ȳ[:, j] .-= ds
             end
         end
         d̄ = ChainRulesCore.Tangent{typeof(d)}(; r=r̄)
@@ -208,10 +207,10 @@ function ChainRulesCore.rrule(
         for i in 1:n
             xi = view(x, :, i)
             yi = view(y, :, i)
-            ds = twoπ .* Δ[i] .* sinpi.(xi .- yi) .* cospi.(xi .- yi) ./ d.r .^ 2
+            ds = π .* Δ[i] .* sinpi.(2 .* (xi .- yi)) ./ d.r .^ 2
             r̄ .-= 2 .* Δ[i] .* sinpi.(xi .- yi) .^ 2 ./ d.r .^ 3
-            x̄[:, i] += ds
-            ȳ[:, i] -= ds
+            x̄[:, i] .+= ds
+            ȳ[:, i] .-= ds
         end
         d̄ = ChainRulesCore.Tangent{typeof(d)}(; r=r̄)
         return NoTangent(), d̄, @thunk(project_x(x̄)), @thunk(project_y(ȳ))