From 16e18150d85c5315c79859138c293ecd101fbe0c Mon Sep 17 00:00:00 2001
From: kshitij12345 <kshitijkalambarkar@gmail.com>
Date: Sun, 19 May 2019 02:51:49 +0530
Subject: [PATCH] add gradient on

---
 .../tensor/elemwise_unary_op_basic.cc         | 34 +++++++++++++------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/src/operator/tensor/elemwise_unary_op_basic.cc b/src/operator/tensor/elemwise_unary_op_basic.cc
index bcd9962834e5..d5e715f80252 100644
--- a/src/operator/tensor/elemwise_unary_op_basic.cc
+++ b/src/operator/tensor/elemwise_unary_op_basic.cc
@@ -989,16 +989,7 @@ The storage type of ``log`` output is always dense
 
 )code" ADD_FILELINE)
 .set_attr<FCompute>("FCompute<cpu>", UnaryOp::LogCompute<cpu, mshadow_op::log>)
-.set_attr<nnvm::FGradient>("FGradient",
-  [](const nnvm::NodePtr& n, const std::vector<nnvm::NodeEntry>& ograds) {
-    auto x_grad = MakeNode("reciprocal", n->attrs.name + "_mid_x_grad",
-                            {n->inputs[0]}, nullptr, &n);
-    auto in_grad = MakeNode("elemwise_mul", n->attrs.name + "_backward",
-                            {ograds[0], nnvm::NodeEntry{x_grad, 0, 0}}, nullptr, &n);
-    std::vector<nnvm::NodeEntry> ret;
-    ret.emplace_back(nnvm::NodeEntry{in_grad, 0, 0});
-    return ret;
-  });
+.set_attr<nnvm::FGradient>("FGradient", ElemwiseGradUseIn{"_backward_log"});
 
 // log10
 MXNET_OPERATOR_REGISTER_UNARY_WITH_SPARSE_DR(log10, cpu, mshadow_op::log10)
@@ -1025,7 +1016,28 @@ The storage type of ``log2`` output is always dense
 .set_attr<nnvm::FGradient>("FGradient", ElemwiseGradUseIn{"_backward_log2"});
 
 MXNET_OPERATOR_REGISTER_BINARY_WITH_SPARSE_CPU_DR(_backward_log,
-                                                  unary_bwd<mshadow_op::log_grad>);
+                                                  unary_bwd<mshadow_op::log_grad>)
+.set_attr<nnvm::FGradient>("FGradient",
+  [](const nnvm::NodePtr& n, const std::vector<nnvm::NodeEntry>& ograds) {
+    // For g(x) -> g = log
+    // g''(x) = -1 * (g'(x) * g'(x))
+    auto gx = nnvm::NodeEntry{n, 0, 0};
+    auto ggx_mid = MakeNode("elemwise_mul", n->attrs.name + "_backward_mid_grad_grad",
+                            {gx, gx}, nullptr, &n);
+    auto ggx = MakeNode("negative", n->attrs.name + "_backward_grad_grad",
+                        {nnvm::NodeEntry{ggx_mid, 0, 0}}, nullptr, &n);
+    auto gxx_chain = MakeNode("elemwise_mul", n->attrs.name + "_backward_grad_grad_inp",
+                             {ograds[0], nnvm::NodeEntry{ggx, 0, 0}}, nullptr, &n);
+
+    // grad
+    auto ggrad_chain = MakeNode("elemwise_mul", n->attrs.name + "_backward_grad_grad",
+                             {ograds[0], gx}, nullptr, &n);
+
+    std::vector<nnvm::NodeEntry> ret;
+    ret.emplace_back(nnvm::NodeEntry{ggrad_chain, 0, 0});
+    ret.emplace_back(nnvm::NodeEntry{gxx_chain, 0, 0});
+    return ret;
+  });
 
 MXNET_OPERATOR_REGISTER_BINARY_WITH_SPARSE_CPU_DR(_backward_log10,
                                                   unary_bwd<mshadow_op::log10_grad>);