Fix typo in maxpool backprop (#134)

Fix typo in `maxpool` backprop

Author: staticfloat

src/impl/pooling_direct.jl

@@ -200,7 +200,7 @@ for name in (:max, :mean)
                 w in w_region
 
                 # Grab the incoming gradient at this index for future use
-                y_idx = dy[w, h, d, c, batch_idx]
+                y_idx = y[w, h, d, c, batch_idx]
                 dy_idx = dy[w, h, d, c, batch_idx]
                 maxpool_already_chose = false
 

test/pooling.jl

@@ -303,3 +303,14 @@ x = rand(10, 10, 3, 10)
 @test size(maxpool(x, (2, 2); pad = (2, 2), stride = (2, 2))) == (7, 7, 3, 10)
 @test size(meanpool(x, (2, 2))) == (5, 5, 3, 10)
 @test size(meanpool(x, (2, 2); pad = (2, 2), stride = (2, 2))) == (7, 7, 3, 10)
+
+# Add another test for 2d maxpool that uses an odd-length size:
+@testset "Issue #133" begin
+    x = reshape([(1.:9.)...], 3, 3, 1, 1)
+    pdims = PoolDims(size(x), (2,2), padding = (1,1), stride = (2,2))
+    y = maxpool(x, pdims)
+
+    dy = y .* 0 .+ 1
+    dx = ∇maxpool(dy, y, x, pdims)
+    @test dx[:,:,1,1] == [1.0 0.0 1.0; 0.0 0.0 0.0; 1.0 0.0 1.0]
+end