!653 add LARSUpdate example in comments

Merge pull request !653 from gziyan/add_lars_example

mindspore/ops/operations/nn_ops.py

@@ -2478,6 +2478,27 @@ class LARSUpdate(PrimitiveWithInfer):
 
     Outputs:
         Tensor, representing the new gradient.
+
+    Examples:
+        >>> from mindspore import Tensor
+        >>> from mindspore.ops import operations as P
+        >>> from mindspore.ops import functional as F
+        >>> import mindspore.nn as nn
+        >>> import numpy as np
+        >>> class Net(nn.Cell):
+        >>>     def __init__(self):
+        >>>         super(Net, self).__init__()
+        >>>         self.lars = P.LARSUpdate()
+        >>>         self.reduce = P.ReduceSum()
+        >>>     def construct(self, weight, gradient):
+        >>>         w_square_sum = self.reduce(F.square(weight))
+        >>>         grad_square_sum = self.reduce(F.square(gradient))
+        >>>         grad_t = self.lars(weight, gradient, w_square_sum, grad_square_sum, 0.0, 1.0)
+        >>>         return grad_t
+        >>> weight = np.random.random(size=(2, 3)).astype(np.float32)
+        >>> gradient = np.random.random(size=(2, 3)).astype(np.float32)
+        >>> net = Net()
+        >>> ms_output = net(Tensor(weight), Tensor(gradient))
     """
 
     @prim_attr_register