Warm-up和Cos设置LR

2020/08/23 11:19
阅读数 734

Warm-up和Cos设置LR

import bisect
from bisect import bisect_right
import matplotlib.pyplot as plt
import numpy as np
import math

lr = []
iters=[]

def _get_warmup_factor_at_iter(
    method: str, iter: int, warmup_iters: int, warmup_factor: float
):
    """
    Return the learning rate warmup factor at a specific iteration.
    See :paper:`in1k1h` for more details.
    Args:
        method (str): warmup method; either "constant" or "linear".
        iter (int): iteration at which to calculate the warmup factor.
        warmup_iters (int): the number of warmup iterations.
        warmup_factor (float): the base warmup factor (the meaning changes according
            to the method used).
    Returns:
        float: the effective warmup factor at the given iteration.
    """
    if iter >= warmup_iters:
        return 1.0

    if method == "constant":
        return warmup_factor
    elif method == "linear":
        alpha = iter / warmup_iters
        return warmup_factor * (1 - alpha) + alpha
    else:
        raise ValueError("Unknown warmup method: {}".format(method))

class WarmupMultiStepLR():
    def __init__(
        self,
        milestones,
        gamma: float = 0.1,
        warmup_factor: float = 0.001,
        warmup_iters: int = 50,
        warmup_method: str = "linear",
    ):
        if not list(milestones) == sorted(milestones):
            raise ValueError(
                "Milestones should be a list of" " increasing integers. Got {}", milestones
            )
        self.milestones = milestones
        self.gamma = gamma
        self.warmup_factor = warmup_factor
        self.warmup_iters = warmup_iters
        self.warmup_method = warmup_method

    def get_lr(self, iter) :
        warmup_factor = _get_warmup_factor_at_iter(
            self.warmup_method, iter, self.warmup_iters, self.warmup_factor
        )
        return [
            base_lr * warmup_factor * self.gamma ** bisect_right(self.milestones, iter)
            for base_lr in [0.001]
        ]


class WarmupCosineLR():
    def __init__(
        self,
        max_iters: int,
        warmup_factor: float = 0.001,
        warmup_iters: int = 50,
        warmup_method: str = "linear",
    ):
        self.max_iters = max_iters
        self.warmup_factor = warmup_factor
        self.warmup_iters = warmup_iters
        self.warmup_method = warmup_method

    def get_lr(self, iter):
        warmup_factor = _get_warmup_factor_at_iter(
            self.warmup_method, iter, self.warmup_iters, self.warmup_factor
        )
        # Different definitions of half-cosine with warmup are possible. For
        # simplicity we multiply the standard half-cosine schedule by the warmup
        # factor. An alternative is to start the period of the cosine at warmup_iters
        # instead of at 0. In the case that warmup_iters << max_iters the two are
        # very close to each other.
        return [
            base_lr
            * warmup_factor
            * 0.5
            * (1.0 + math.cos(math.pi * iter / self.max_iters))
            for base_lr in [0.01]]

coslr = WarmupCosineLR(max_iters = 500)
linlr = WarmupMultiStepLR(milestones=[50,200,400])
for iter in range(500):

    lr.append(linlr.get_lr(iter))
    iters.append(iter)
plt.plot(iters,lr)
plt.show()

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