Source code for mindspore.nn.optim.momentum

# Copyright 2020 Huawei Technologies Co., Ltd
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"""momentum"""
from mindspore.ops import functional as F, composite as C
from mindspore.ops import _selected_ops
from mindspore.common.parameter import Parameter
from mindspore.common.tensor import Tensor
import mindspore.common.dtype as mstype
from mindspore._checkparam import check_bool
from mindspore._checkparam import Validator as validator
from .optimizer import Optimizer

_momentum_opt = C.MultitypeFuncGraph("momentum_opt")


@_momentum_opt.register("Function", "Tensor", "Tensor", "Tensor", "Tensor", "Tensor")
def _tensor_run_opt_ext(opt, momentum, learning_rate, gradient, weight, moment):
    """Apply momentum optimizer to the weight parameter using Tensor."""
    success = True
    success = F.depend(success, opt(weight, moment, learning_rate, gradient, momentum))
    return success


[docs]class Momentum(Optimizer): """ Implements the Momentum algorithm. Refer to the paper on the importance of initialization and momentum in deep learning for more details. Note: The Momentum optimizer supports separating parameter groups. Different parameter groups can set different `learning_rate` and `weight_decay`. When separating parameter groups, the weight decay in each group will be applied on the parameters if the value of weight_decay > 0. When not separating parameter groups, the `weight_decay` in the API will be applied on the parameters if `weight_decay` > 0 and the 'beta' and 'gamma' are not in the name of parameters. To improve parameter groups performance, the customized order of parameters can be supported. Args: params (Union[list[Parameter], list[dict]]): When the `params` is a list of `Parameter` which will be updated, the element in `params` should be class `Parameter`. When the `params` is a list of `dict`, the "params", "lr", "weight_decay" and "order_params" are the keys can be parsed. - params: Required. The value should be a list of `Parameter`. - lr: Optional. If "lr" in the keys, the value of corresponding learning rate will be used. If not, the `learning_rate` in the API will be used. - weight_decay: Optional. If "weight_decay" in the keys, the value of corresponding weight decay will be used. If not, the `weight_decay` in the API will be used. - order_params: Optional. If "order_params" in the keys, the value should be the order of parameters and the order will be followed in optimizer. There are no other keys in the `dict` and the parameters which in the value of 'order_params' but not in any group will use default learning rate and default weight decay. learning_rate (Union[int, float, Tensor, Iterable]): A value for the learning rate. When the learning_rate is Iterable or a Tensor and the dims of the Tensor is 1, use dynamic learning rate, then the i-th step will take the i-th value as the learning rate. When the learning_rate is float or learning_rate is a Tensor but the dims of the Tensor is 0, use fixed learning rate. Other cases are not supported. It should be equal to or greater than 0.0. momentum (float): Hyperparameter of type float, means momentum for the moving average. It should be at least 0.0. weight_decay (int, float): Weight decay (L2 penalty). It should be equal to or greater than 0.0. Default: 0.0. loss_scale (int, float): A floating point value for the loss scale. It should be greater than 0.0. Default: 1.0. use_nesterov (bool): Enable Nesterov momentum. Default: False. Inputs: - **gradients** (tuple[Tensor]) - The gradients of `params`, the shape is the same as `params`. Outputs: tuple[bool], all elements are True. Raises: ValueError: If the momentum is less than 0.0. Examples: >>> net = Net() >>> #1) All parameters use the same learning rate and weight decay >>> optim = nn.Momentum(params=net.trainable_params(), learning_rate=0.1, momentum=0.9) >>> >>> #2) Use parameter groups and set different values >>> conv_params = list(filter(lambda x: 'conv' in x.name, net.trainable_params())) >>> bias_params = list(filter(lambda x: 'bias' in x.name, net.trainable_params())) >>> group_params = [{'params': conv_params, 'weight_decay': 0.01}, >>> {'params': bias_params, 'lr': 0.01}, >>> {'order_params': net.trainable_params()}] >>> opt = nn.Momentum(group_params, learning_rate=0.1, momentum=0.9, weight_decay=0.0) >>> # The conv_params's parameters will use a learning rate of default value 0.1 and a weight decay of 0.01. >>> # The bias_params's parameters will use a learning rate of 0.01 and a weight decay of default value 0.0. >>> # The final parameters order in which the optimizer will be followed is the value of 'order_params'. >>> # The parameters which in the value of 'order_params' but not in any group will use a learning rate >>> # of default value 0.1 and a weight decay of default value 0.0. >>> >>> loss = nn.SoftmaxCrossEntropyWithLogits() >>> model = Model(net, loss_fn=loss, optimizer=optim, metrics=None) """ def __init__(self, params, learning_rate, momentum, weight_decay=0.0, loss_scale=1.0, use_nesterov=False): super(Momentum, self).__init__(learning_rate, params, weight_decay, loss_scale) validator.check_value_type("momentum", momentum, [float], self.cls_name) if isinstance(momentum, float) and momentum < 0.0: raise ValueError("momentum should be at least 0.0, but got momentum {}".format(momentum)) self.momentum = Parameter(Tensor(momentum, mstype.float32), name="momentum") self.params = self.parameters self.use_nesterov = check_bool(use_nesterov) self.moments = self.params.clone(prefix="moments", init='zeros') self.hyper_map = C.HyperMap() self.opt = _selected_ops.ApplyMomentum(use_nesterov=self.use_nesterov) def construct(self, gradients): params = self.params moments = self.moments gradients = self.decay_weight(gradients) gradients = self.scale_grad(gradients) lr = self.get_lr() if self.is_group_lr: success = self.hyper_map(F.partial(_momentum_opt, self.opt, self.momentum), lr, gradients, params, moments) else: success = self.hyper_map(F.partial(_momentum_opt, self.opt, self.momentum, lr), gradients, params, moments) return success