Momentum Velocity init in Momentum.__init__() (#29223)

* add lamb optimizer and unittest

* fix momentum resume training

* fix momentum acc

python/paddle/fluid/tests/unittests/test_momentum_op.py

@@ -294,7 +294,6 @@ class TestMomentumV2(unittest.TestCase):
 
     def test_momentum(self):
         paddle.enable_static()
-
         place = fluid.CPUPlace()
         main = fluid.Program()
         with fluid.program_guard(main):

python/paddle/optimizer/momentum.py

@@ -16,6 +16,8 @@ from .optimizer import Optimizer
 from ..fluid import core
 from ..fluid import framework
 from ..fluid.framework import Variable, name_scope
+from ..fluid.layer_helper import LayerHelper
+import paddle.fluid as fluid
 
 __all__ = ["Momentum"]
 
@@ -105,12 +107,20 @@ class Momentum(Optimizer):
         self.type = "momentum"
         self._momentum = momentum
         self._use_nesterov = bool(use_nesterov)
+        if framework.in_dygraph_mode():
+            self.helper = LayerHelper(self.__class__.__name__)
+            for p in parameters:
+                self._add_accumulator(self._velocity_acc_str, p)
+        else:
+            all_parameters = fluid.default_main_program().global_block(
+            ).all_parameters()
+            self.helper = LayerHelper(self.__class__.__name__)
+            for p in all_parameters:
+                self._add_accumulator(self._velocity_acc_str, p)
 
     def _create_accumulators(self, block, parameters):
         assert isinstance(block, framework.Block)
-
-        for p in parameters:
-            self._add_accumulator(self._velocity_acc_str, p)
+        # create accumulator in init func, so no implementation here
 
     def _append_optimize_op(self, block, param_and_grad):
         assert isinstance(block, framework.Block)