From d432b10d8aa5beb0e8576b8f9811048af98519bc Mon Sep 17 00:00:00 2001
From: dangqingqing <dangqingqing@baidu.com>
Date: Tue, 5 Dec 2017 13:45:17 +0800
Subject: [PATCH] Update cuda kernel and doc.

---
 paddle/operators/momentum_op.cc | 8 ++++++--
 paddle/operators/momentum_op.cu | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/paddle/operators/momentum_op.cc b/paddle/operators/momentum_op.cc
index fde253b0b38..2ab48fedecf 100644
--- a/paddle/operators/momentum_op.cc
+++ b/paddle/operators/momentum_op.cc
@@ -71,8 +71,12 @@ class MomentumOpMaker : public framework::OpProtoAndCheckerMaker {
              "(Tensor, default Tensor<float>) "
              "Input learning rate");
 
-    AddOutput("ParamOut", "(Tensor) Output updated parameter");
-    AddOutput("VelocityOut", "(Tensor) Output updated velocity");
+    AddOutput("ParamOut",
+              "(Tensor) This output is updated parameter. "
+              "It shared memory with Input(Param).");
+    AddOutput("VelocityOut",
+              "(Tensor) This output is updated velocity. "
+              "It shared memory with Input(Velocity).");
 
     AddAttr<float>("mu", "(float) Momentum coefficient");
     AddAttr<bool>("use_nesterov",
diff --git a/paddle/operators/momentum_op.cu b/paddle/operators/momentum_op.cu
index d856df40027..be0c8ea0717 100644
--- a/paddle/operators/momentum_op.cu
+++ b/paddle/operators/momentum_op.cu
@@ -29,7 +29,7 @@ __global__ void MomentumKernel(const T* p, const T* g, const T* v,
       T g_val = g[i];
       T v_new = v[i] * mu + g_val;
       v_out[i] = v_new;
-      p_out[i] = p[i] - g_val * lr + v_new * mu * lr;
+      p_out[i] = p[i] - (g_val - v_new * mu) * lr;
     }
   } else {
     for (int i = blockIdx.x * blockDim.x + threadIdx.x; i < num;
-- 
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