From 264b644718c14da348114bb9a44afddcd7166f11 Mon Sep 17 00:00:00 2001
From: dongzhihong <dzhwinter@gmail.com>
Date: Wed, 2 Aug 2017 21:26:29 +0800
Subject: [PATCH] "add rowwise add backward op"

---
 paddle/operators/rowwise_add_op.cc | 15 +++++++++++++++
 paddle/operators/rowwise_add_op.h  | 19 +++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/paddle/operators/rowwise_add_op.cc b/paddle/operators/rowwise_add_op.cc
index 2ad2b66c8..cc763a8cf 100644
--- a/paddle/operators/rowwise_add_op.cc
+++ b/paddle/operators/rowwise_add_op.cc
@@ -46,6 +46,17 @@ for i in xrange(X.shape[0]):
 )DOC");
   }
 };
+class RowWiseAddGradOp : public OperatorWithKernel {
+protected:
+  void InferShape(const InferShapeContext &ctx) const override {
+    PADDLE_ENFORCE(ctx.InputSize() == 4UL,
+                   "RowWiseAddGrad inputs is I, O, OG, size must be 4");
+    PADDLE_ENFORCE(ctx.OutputSize() == 2,
+                   "RowWiseAddGrad output is IG, size must be 2");
+    ctx.Output<Tensor>(0)->Resize(ctx.Input<Tensor>(0)->dims());
+    ctx.Output<Tensor>(1)->Resize(ctx.Input<Tensor>(1)->dims());
+  }
+};
 
 }  // namespace operators
 }  // namespace paddle
@@ -53,3 +64,7 @@ for i in xrange(X.shape[0]):
 REGISTER_OP(rowwise_add, ops::RowWiseAddOp, ops::RowWiseAddOpMaker);
 REGISTER_OP_CPU_KERNEL(rowwise_add,
                        ops::RowWiseAddKernel<ops::CPUPlace, float>);
+
+REGISTER_GRADIENT_OP(rowwise_add, rowwise_add_grad, ops::RowWiseAddGradOp);
+REGISTER_OP_CPU_KERNEL(rowwise_add_grad,
+                       ops::RowWiseAddGradKernel<ops::CPUPlace, float>);
diff --git a/paddle/operators/rowwise_add_op.h b/paddle/operators/rowwise_add_op.h
index b86dd5463..940459e0f 100644
--- a/paddle/operators/rowwise_add_op.h
+++ b/paddle/operators/rowwise_add_op.h
@@ -38,5 +38,24 @@ public:
   }
 };
 
+template <typename Place, typename T>
+class RowWiseAddGradKernel : public OpKernel {
+public:
+  void Compute(const ExecutionContext& context) const override {
+    auto XGrad = context.Output<Tensor>(0);
+    auto bGrad = context.Output<Tensor>(1);
+    XGrad->mutable_data<T>(context.GetPlace());
+    bGrad->mutable_data<T>(context.GetPlace());
+
+    // I, O, OG  => [X, b], [Out], [OutGrad]
+    auto OutGrad = EigenMatrix<T>::From(*context.Input<Tensor>(3));
+    EigenMatrix<T>::From(*XGrad).device(*(context.GetEigenDevice<Place>())) =
+        OutGrad;
+    // const int dimension = bGrad.dimension(0);
+    // https://eigen.tuxfamily.org/dox/unsupported/TensorBase_8h_source.html
+    EigenVector<T>::Flatten(*bGrad).device(*(context.GetEigenDevice<Place>())) =
+        OutGrad.cumsum(1);  // colwise add
+  }
+};
 }  // namespace operators
 }  // namespace paddle
-- 
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