From 2dd6872e7c920dc9faec4b122e83a136d6369059 Mon Sep 17 00:00:00 2001
From: chenguowei01 <chenguowei01@baidu.com>
Date: Thu, 30 Jul 2020 20:33:28 +0800
Subject: [PATCH] update train.py

---
 dygraph/core/train.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/dygraph/core/train.py b/dygraph/core/train.py
index 0bbcabf1..9563f0c3 100644
--- a/dygraph/core/train.py
+++ b/dygraph/core/train.py
@@ -87,6 +87,7 @@ def train(model,
             labels = data[1].astype('int64')
             if nranks > 1:
                 loss = ddp_model(images, labels)
+                # apply_collective_grads sum grads over multiple gpus.
                 loss = ddp_model.scale_loss(loss)
                 loss.backward()
                 ddp_model.apply_collective_grads()
-- 
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