clip.py

#   Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserve.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import copy

import functools
import layers
import framework
from . import core

__all__ = [
    'ErrorClipByValue',
    'GradientClipByValue',
    'GradientClipByNorm',
    'GradientClipByGlobalNorm',
    'append_gradient_clip_ops',
    'error_clip_callback',
]


class BaseErrorClipAttr(object):
    def append_clip_op(self, block, grad_name):
        raise NotImplementedError()


class ErrorClipByValue(BaseErrorClipAttr):
    def __init__(self, max, min=None):
        max = float(max)
        if min is None:
            min = -max
        else:
            min = float(min)
        self.max = max
        self.min = min

    def append_clip_op(self, block, grad_name):
        clip_op_desc = block.desc.append_op()
        clip_op_desc.set_type("clip")
        clip_op_desc.set_input("X", [grad_name])
        clip_op_desc.set_output("Out", [grad_name])
        clip_op_desc.set_attr("min", self.min)
        clip_op_desc.set_attr("max", self.max)


def error_clip_callback(block, context):
    # the context is a grad_to_var map
    grad_to_var = context
    op_desc = block.desc.op(block.desc.op_size() - 1)
    for grad_n in filter(lambda n: grad_to_var.has_key(n),
                         op_desc.output_arg_names()):
        fwd_var = block.var_recursive(grad_to_var[grad_n])
        error_clip = getattr(fwd_var, "error_clip", None)
        if not (error_clip is None or isinstance(error_clip,
                                                 BaseErrorClipAttr)):
            raise TypeError(
                "Variable's error_clip should be an instance of BaseErrorClipAttr or None."
            )
        if error_clip is not None:
            error_clip.append_clip_op(block, grad_n)


class BaseGradientClipAttr(object):
    def process_context(self, context, param, grad):
        raise NotImplementedError()

    def create_operators(self, param, grad):
        raise NotImplementedError()


class NullGradientClipAttr(BaseGradientClipAttr):
    def process_context(self, context, param, grad):
        pass

    def create_operators(self, param, grad):
        return param, grad


class GradientClipByValue(BaseGradientClipAttr):
    def __init__(self, max, min=None):
        max = float(max)
        if min is None:
            min = -max
        else:
            min = float(min)
        self.max = max
        self.min = min

    def process_context(self, context, param, grad):
        pass

    def create_operators(self, param, grad):
        new_grad = layers.clip(x=grad, min=self.min, max=self.max)
        return param, new_grad


class GradientClipByNorm(BaseGradientClipAttr):
    def __init__(self, clip_norm):
        self.clip_norm = clip_norm

    def process_context(self, context, param, grad):
        pass

    def create_operators(self, param, grad):
        new_grad = layers.clip_by_norm(x=grad, max_norm=self.clip_norm)
        return param, new_grad


class GradientClipByGlobalNorm(BaseGradientClipAttr):
    def __init__(self, clip_norm, group_name="default_group"):
        if not isinstance(group_name, basestring):
            raise TypeError("'group_name' must be a basestring.")

        self.clip_norm = clip_norm
        self.group_name = group_name

    def process_context(self, context, param, grad):
        if self.group_name not in context:
            context[self.group_name] = []
            context[self.group_name + "_clip_value"] = self.clip_norm
            context[self.group_name + "_clip"] = layers.fill_constant(
                shape=[1], dtype="float32", value=self.clip_norm)
        else:
            if not self.clip_norm == context[self.group_name + "_clip_value"]:
                raise ValueError(
                    "All parameters' 'clip_norm' of a same group should be the same"
                )

        local_norm_var = layers.reduce_sum(input=layers.pow(x=grad, factor=2.0))
        context[self.group_name].append(local_norm_var)

        self.context = context

    def create_operators(self, param, grad):
        group_scale_name = self.group_name + "_scale"
        if group_scale_name not in self.context:
            group_norm_var = layers.sums(input=self.context[self.group_name])
            layers.sqrt(x=group_norm_var, out=group_norm_var)
            clip_var = self.context[self.group_name + "_clip"]
            group_scale_var = layers.elementwise_div(
                x=clip_var,
                y=layers.elementwise_max(
                    x=clip_var, y=group_norm_var))
            assert group_scale_var.shape == (1L, )
            self.context[group_scale_name] = group_scale_var

        new_grad = layers.elementwise_mul(
            x=grad, y=self.context[group_scale_name])
        return param, new_grad


def set_gradient_clip(clip, param_list=None, program=None):
    """
        To specify parameters that require gradient clip.
        Args:
            clip(BaseGradientClipAttr): An instance of some derived class of BaseGradientClipAttr, 
                    which describes the type and detailed attributes of required gradient clip.
            param_list(list, None by default): Parameters that require gradient clip. 
                    It can be a list of parameter or a list of parameter's name. 
                    When it's None, all parameters in the program will be included. 
            program(Program, None by default): The program where parameters are. 
                    Will be the default main program when assigned with None.
    """
    if not isinstance(clip, BaseGradientClipAttr):
        raise TypeError(
            "'clip' should be an instance of BaseGradientClipAttr's derived class"
        )
    if program is None:
        program = framework.default_main_program()
    if param_list is None:
        param_list = program.block(0).all_parameters()
    if all(isinstance(elem, basestring) for elem in param_list):
        param_list = [program.block(0).var(elem) for elem in param_list]
    if not all(isinstance(elem, framework.Parameter) for elem in param_list):
        raise TypeError(
            "'param_list' should be a list of Parameter or basestring(parameter's name)."
        )

    for param in param_list:
        param.gradient_clip_attr = copy.deepcopy(clip)


def append_gradient_clip_ops(param_grad):
    context = dict()
    create_op_callbacks = []
    for p, g in param_grad:
        clip_attr = getattr(p, 'gradient_clip_attr', NullGradientClipAttr())
        if clip_attr is None:
            clip_attr = NullGradientClipAttr()
        if not isinstance(clip_attr, BaseGradientClipAttr):
            raise TypeError(
                "clip attribute should be an instance of BaseGradientClipAttr")

        clip_attr.process_context(context=context, param=p, grad=g)
        create_op_callbacks.append(
            functools.partial(
                clip_attr.create_operators, param=p, grad=g))

    return [each_callback() for each_callback in create_op_callbacks]


ClipByValue = GradientClipByValue