fix the doc in elementwise_add elementwise_sub elementwise_mul elementwise_div

fix the doc in elementwise ops，add the override function in the doc

python/paddle/fluid/layers/nn.py

@@ -10407,13 +10407,14 @@ Examples:
         x = fluid.data(name="x", shape=[3], dtype='float32')
         y = fluid.data(name="y", shape=[3], dtype='float32')
         z = fluid.layers.elementwise_add(x, y)
+        # z = x + y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
         z_value = exe.run(feed=gen_data(),
                             fetch_list=[z.name])
 
-        print(z_value) #[3., 8., 6.]
+        print(z_value) # [3., 8., 6.]
 
 
     .. code-block:: python
@@ -10430,6 +10431,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[3,4], dtype='float32')
         z = fluid.layers.elementwise_add(x, y, axis=1)
+        # z = x + y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10454,6 +10456,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[5], dtype='float32')
         z = fluid.layers.elementwise_add(x, y, axis=3)
+        # z = x + y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10488,13 +10491,14 @@ Examples:
         x = fluid.data(name="x", shape=[3], dtype='float32')
         y = fluid.data(name="y", shape=[3], dtype='float32')
         z = fluid.layers.elementwise_div(x, y)
+        # z = x / y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
         z_value = exe.run(feed=gen_data(),
                             fetch_list=[z.name])
 
-        print(z_value) #[2., 0.6, 2.]
+        print(z_value) # [2., 0.6, 2.]
 
 
     .. code-block:: python
@@ -10511,6 +10515,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[3,4], dtype='float32')
         z = fluid.layers.elementwise_div(x, y, axis=1)
+        # z = x / y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10535,6 +10540,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[5], dtype='float32')
         z = fluid.layers.elementwise_div(x, y, axis=3)
+        # z = x / y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10569,13 +10575,14 @@ Examples:
         x = fluid.data(name="x", shape=[3], dtype='float32')
         y = fluid.data(name="y", shape=[3], dtype='float32')
         z = fluid.layers.elementwise_sub(x, y)
+        # z = x - y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
         z_value = exe.run(feed=gen_data(),
                             fetch_list=[z.name])
 
-        print(z_value) #[1., -2., 2.]
+        print(z_value) # [1., -2., 2.]
 
 
     .. code-block:: python
@@ -10592,6 +10599,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[3,4], dtype='float32')
         z = fluid.layers.elementwise_sub(x, y, axis=1)
+        # z = x - y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10616,6 +10624,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[5], dtype='float32')
         z = fluid.layers.elementwise_sub(x, y, axis=3)
+        # z = x - y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10650,13 +10659,14 @@ Examples:
         x = fluid.data(name="x", shape=[3], dtype='float32')
         y = fluid.data(name="y", shape=[3], dtype='float32')
         z = fluid.layers.elementwise_mul(x, y)
+        # z = x * y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
         z_value = exe.run(feed=gen_data(),
                             fetch_list=[z.name])
 
-        print(z_value) #[2., 15., 8.]
+        print(z_value) # [2., 15., 8.]
 
 
     .. code-block:: python
@@ -10673,6 +10683,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[3,4], dtype='float32')
         z = fluid.layers.elementwise_mul(x, y, axis=1)
+        # z = x * y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)
@@ -10697,6 +10708,7 @@ Examples:
         x = fluid.data(name="x", shape=[2,3,4,5], dtype='float32')
         y = fluid.data(name="y", shape=[5], dtype='float32')
         z = fluid.layers.elementwise_mul(x, y, axis=3)
+        # z = x * y
 
         place = fluid.CPUPlace()
         exe = fluid.Executor(place)