!199 Fix the bug of weight decay for `Adam` optimizer

Merge pull request !199 from seatea/adam-weight-decay

mindspore/nn/optim/adam.py

@@ -166,7 +166,8 @@ class Adam(Optimizer):
     """
 
     def __init__(self, params, learning_rate=1e-3, beta1=0.9, beta2=0.999, eps=1e-8, use_locking=False,
-                 use_nesterov=False, weight_decay=0.0, loss_scale=1.0):
+                 use_nesterov=False, weight_decay=0.0, loss_scale=1.0,
+                 decay_filter=lambda x: 'beta' not in x.name and 'gamma' not in x.name):
         super(Adam, self).__init__(learning_rate, params)
         _check_param_value(beta1, beta2, eps, weight_decay)
         validator.check_type("use_locking", use_locking, [bool])
@@ -192,6 +193,7 @@ class Adam(Optimizer):
         self.moment1 = self.parameters.clone(prefix="moment1", init='zeros')
         self.moment2 = self.parameters.clone(prefix="moment2", init='zeros')
 
+        self.decay_tf = tuple(decay_filter(x) for x in self.parameters)
         self.hyper_map = C.HyperMap()
         self.opt = P.Adam(use_locking, use_nesterov)
         self.weight_decay = weight_decay * loss_scale