Update common.py

Author: GeiduanLiu

source/train/common.py

@@ -1,14 +1,28 @@
 import os,warnings,fnmatch
 import numpy as np
+import math
 from deepmd.env import tf
 
+def gelu(x):
+    """Gaussian Error Linear Unit.
+    This is a smoother version of the RELU.
+    Original paper: https://arxiv.org/abs/1606.08415
+    Args:
+    x: float Tensor to perform activation.
+    Returns:
+    `x` with the GELU activation applied.
+    """
+    cdf = 0.5 * (1.0 + tf.tanh((math.sqrt(2 / math.pi) * (x + 0.044715 * tf.pow(x, 3)))))
+    return x * cdf
+
 data_requirement = {}
 activation_fn_dict = {
     "relu": tf.nn.relu,
     "relu6": tf.nn.relu6,
     "softplus": tf.nn.softplus,
     "sigmoid": tf.sigmoid,
-    "tanh": tf.nn.tanh
+    "tanh": tf.nn.tanh,
+    "gelu": gelu
 }
 def add_data_requirement(key, 
                          ndof,