[GitHub] [incubator-mxnet] kshitij12345 commented on a change in pull request #15480: [MXNET-978] Higher Order Gradient Support `elemwise_mul`, `elemwise_add`.

[GitBox <gi...@apache.org>]

kshitij12345 commented on a change in pull request #15480: [MXNET-978] Higher Order Gradient Support `elemwise_mul`, `elemwise_add`.
URL: https://github.com/apache/incubator-mxnet/pull/15480#discussion_r300922295
 
 

 ##########
 File path: src/operator/tensor/elemwise_binary_op_basic.cc
 ##########
 @@ -251,7 +251,31 @@ NNVM_REGISTER_OP(_backward_mul)
 .set_attr<FCompute>("FCompute<cpu>", ElemwiseBinaryOp::BackwardUseIn<
   cpu, mshadow_op::right, mshadow_op::left>)
 .set_attr<FComputeEx>("FComputeEx<cpu>", ElemwiseBinaryOp::BackwardUseInEx<
-  cpu, mshadow_op::right, mshadow_op::left>);
+  cpu, mshadow_op::right, mshadow_op::left>)
+.set_attr<nnvm::FGradient>("FGradient",
+  [](const nnvm::NodePtr& n, const std::vector<nnvm::NodeEntry>& ograds) {
+    // z = x * y
+    // NodeEntry{n, 0, 0} : z_grad * y
+    // NodeEntry{n, 1, 0} : z_grad * x
+    // n->inputs[0] : z_grad
+    // n->inputs[1] : x
+    // n->inputs[1] : y
+    // ograds[0] : head_grads
+    // f(x, y) = x * y
+    // dx = z_grad * y, dy = z_grad * x
+    // d2x = 0, d2y = 0, dz_grad = dx + dy = y + x
+    auto dz_grad = MakeNode("elemwise_add", n->attrs.name + "_y_add_x",
+                            {n->inputs[2], n->inputs[1]}, nullptr, &n);
+
+    std::vector<nnvm::NodeEntry> ret;
+    ret.emplace_back(MakeNode("elemwise_mul", n->attrs.name + "_backward_grad_grad",
+                              {ograds[0], nnvm::NodeEntry{dz_grad}}, nullptr, &n));
+    ret.emplace_back(MakeNode("zeros_like", n->attrs.name + "_backward_grad_grad_x",
 
 Review comment:
   Ah. Right. Thank You.

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