MomentumOptimizer¶
- class paddle.fluid.optimizer. MomentumOptimizer ( learning_rate, momentum, parameter_list=None, use_nesterov=False, regularization=None, grad_clip=None, name=None ) [源代码] ¶
该接口实现含有速度状态的Simple Momentum 优化器
该优化器含有牛顿动量标志,公式更新如下:
参数¶
learning_rate (float|Variable) - 学习率,用于参数更新。作为数据参数,可以是浮点型值或含有一个浮点型值的变量。
momentum (float) - 动量因子。
parameter_list (list,可选) - 指定优化器需要优化的参数。在动态图模式下必须提供该参数;在静态图模式下默认值为None,这时所有的参数都将被优化。
use_nesterov (bool,可选) - 赋能牛顿动量,默认值False。
regularization (WeightDecayRegularizer,可选) - 正则化方法。支持两种正则化策略:cn_api_fluid_regularizer_L1Decay 、 cn_api_fluid_regularizer_L2Decay。如果一个参数已经在 ParamAttr 中设置了正则化,这里的正则化设置将被忽略; 如果没有在 ParamAttr 中设置正则化,这里的设置才会生效。默认值为None,表示没有正则化。
grad_clip (GradientClipBase,可选) – 梯度裁剪的策略,支持三种裁剪策略:cn_api_fluid_clip_GradientClipByGlobalNorm 、 cn_api_fluid_clip_GradientClipByNorm 、 cn_api_fluid_clip_GradientClipByValue 。 默认值为None,此时将不进行梯度裁剪。
name (str,可选) - 具体用法请参见 Name,一般无需设置,默认值为 None。
代码示例¶
import paddle
import paddle.fluid as fluid
import numpy as np
place = fluid.CPUPlace()
main = fluid.Program()
with fluid.program_guard(main):
x = fluid.layers.data(name='x', shape=[13], dtype='float32')
y = fluid.layers.data(name='y', shape=[1], dtype='float32')
y_predict = fluid.layers.fc(input=x, size=1, act=None)
cost = fluid.layers.square_error_cost(input=y_predict, label=y)
avg_cost = fluid.layers.mean(cost)
moment_optimizer = fluid.optimizer.MomentumOptimizer(learning_rate=0.001, momentum=0.9)
moment_optimizer.minimize(avg_cost)
fetch_list = [avg_cost]
train_reader = paddle.batch(
paddle.dataset.uci_housing.train(), batch_size=1)
feeder = fluid.DataFeeder(place=place, feed_list=[x, y])
exe = fluid.Executor(place)
exe.run(fluid.default_startup_program())
for data in train_reader():
exe.run(main, feed=feeder.feed(data), fetch_list=fetch_list)
方法¶
minimize(loss, startup_program=None, parameter_list=None, no_grad_set=None)¶
为网络添加反向计算过程,并根据反向计算所得的梯度,更新parameter_list中的Parameters,最小化网络损失值loss。
参数
loss (Variable) – 需要最小化的损失值变量
startup_program (Program,可选) – 用于初始化parameter_list中参数的 Program,默认值为None,此时将使用 default_startup_program
parameter_list (list,可选) – 待更新的Parameter或者Parameter.name组成的列表,默认值为None,此时将更新所有的Parameter
no_grad_set (set,可选) – 不需要更新的Parameter或者Parameter.name组成的集合,默认值为None
- 返回
-
tuple(optimize_ops, params_grads),其中optimize_ops为参数优化OP列表;param_grads为由(param, param_grad)组成的列表,其中param和param_grad分别为参数和参数的梯度。该返回值可以加入到
Executor.run()
接口的fetch_list
参数中,若加入,则会重写use_prune
参数为True,并根据feed
和fetch_list
进行剪枝,详见Executor
的文档。 - 返回类型
-
tuple
代码示例
import paddle
import paddle.fluid as fluid
import numpy as np
place = fluid.CPUPlace()
main = fluid.Program()
with fluid.program_guard(main):
x = fluid.layers.data(name='x', shape=[13], dtype='float32')
y = fluid.layers.data(name='y', shape=[1], dtype='float32')
y_predict = fluid.layers.fc(input=x, size=1, act=None)
cost = fluid.layers.square_error_cost(input=y_predict, label=y)
avg_cost = fluid.layers.mean(cost)
moment_optimizer = fluid.optimizer.MomentumOptimizer(learning_rate=0.001, momentum=0.9)
moment_optimizer.minimize(avg_cost)
fetch_list = [avg_cost]
train_reader = paddle.batch(
paddle.dataset.uci_housing.train(), batch_size=1)
feeder = fluid.DataFeeder(place=place, feed_list=[x, y])
exe = fluid.Executor(place)
exe.run(fluid.default_startup_program())
for data in train_reader():
exe.run(main, feed=feeder.feed(data), fetch_list=fetch_list)
clear_gradients()¶
注意:
1. 该API只在 Dygraph 模式下生效
清除需要优化的参数的梯度。
代码示例
import paddle.fluid as fluid
import numpy as np
with fluid.dygraph.guard():
value = np.arange(26).reshape(2, 13).astype("float32")
a = fluid.dygraph.to_variable(value)
linear = fluid.Linear(13, 5, dtype="float32")
optimizer = fluid.optimizer.MomentumOptimizer(learning_rate=0.001, momentum=0.9,
parameter_list=linear.parameters())
out = linear(a)
out.backward()
optimizer.minimize(out)
optimizer.clear_gradients()
set_lr()¶
注意:
1. 该API只在 Dygraph 模式下生效
手动设置当前 optimizer
的学习率。当使用LearningRateDecay时,无法使用该API手动设置学习率,因为这将导致冲突。
参数
value (float|Variable) - 需要设置的学习率的值。
返回 无
代码示例
import paddle.fluid as fluid
with fluid.dygraph.guard():
linear = fluid.dygraph.nn.Linear(10, 10)
adam = fluid.optimizer.Adam(0.1, parameter_list=linear.parameters())
# 通过Python float数值手动设置学习率
lr_list = [0.2, 0.3, 0.4, 0.5, 0.6]
for i in range(5):
adam.set_lr(lr_list[i])
print("current lr is {}".format(adam.current_step_lr()))
# 打印结果:
# current lr is 0.2
# current lr is 0.3
# current lr is 0.4
# current lr is 0.5
# current lr is 0.6
# 通过 框架的Variable 设置学习率
lr_var = fluid.layers.create_global_var(shape=[1], value=0.7, dtype='float32')
adam.set_lr(lr_var)
print("current lr is {}".format(adam.current_step_lr()))
# 打印结果:
# current lr is 0.7
current_step_lr()¶
注意:
1. 该API只在 Dygraph 模式下生效
获取当前步骤的学习率。当不使用LearningRateDecay时,每次调用的返回值都相同,否则返回当前步骤的学习率。
返回 当前步骤的学习率。
返回类型 float
代码示例
import paddle.fluid as fluid
import numpy as np
# example1: LearningRateDecay is not used, return value is all the same
with fluid.dygraph.guard():
emb = fluid.dygraph.Embedding([10, 10])
adam = fluid.optimizer.Adam(0.001, parameter_list = emb.parameters())
lr = adam.current_step_lr()
print(lr) # 0.001
# example2: PiecewiseDecay is used, return the step learning rate
with fluid.dygraph.guard():
inp = np.random.uniform(-0.1, 0.1, [10, 10]).astype("float32")
linear = fluid.dygraph.nn.Linear(10, 10)
inp = fluid.dygraph.to_variable(inp)
out = linear(inp)
loss = fluid.layers.reduce_mean(out)
bd = [2, 4, 6, 8]
value = [0.2, 0.4, 0.6, 0.8, 1.0]
adam = fluid.optimizer.Adam(fluid.dygraph.PiecewiseDecay(bd, value, 0),
parameter_list=linear.parameters())
# first step: learning rate is 0.2
np.allclose(adam.current_step_lr(), 0.2, rtol=1e-06, atol=0.0) # True
# learning rate for different steps
ret = [0.2, 0.2, 0.4, 0.4, 0.6, 0.6, 0.8, 0.8, 1.0, 1.0, 1.0, 1.0]
for i in range(12):
adam.minimize(loss)
lr = adam.current_step_lr()
np.allclose(lr, ret[i], rtol=1e-06, atol=0.0) # True