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# -*- coding: utf-8 -*-
# Author: Gaojian Wang@ZJUICSR
# --------------------------------------------------------
# This source code is licensed under the Attribution-NonCommercial 4.0 International License.
# You can find the license in the LICENSE file in the root directory of this source tree.
# --------------------------------------------------------
import math
import numpy as np
def adjust_learning_rate(optimizer, epoch, args):
"""Decay the learning rate with half-cycle cosine after warmup"""
if epoch < args.warmup_epochs:
lr = args.lr * epoch / args.warmup_epochs
else:
lr = args.min_lr + (args.lr - args.min_lr) * 0.5 * \
(1. + math.cos(math.pi * (epoch - args.warmup_epochs) / (args.epochs - args.warmup_epochs)))
for param_group in optimizer.param_groups:
if "lr_scale" in param_group:
param_group["lr"] = lr * param_group["lr_scale"]
else:
param_group["lr"] = lr
return lr
def cosine_scheduler(base_value, final_value, epochs, niter_per_ep, warmup_epochs=0,
start_warmup_value=0, warmup_steps=-1):
warmup_schedule = np.array([])
warmup_iters = warmup_epochs * niter_per_ep
if warmup_steps > 0:
warmup_iters = warmup_steps
print("Set warmup steps = %d" % warmup_iters)
if warmup_epochs > 0:
warmup_schedule = np.linspace(start_warmup_value, base_value, warmup_iters)
iters = np.arange(epochs * niter_per_ep - warmup_iters)
schedule = np.array(
[final_value + 0.5 * (base_value - final_value) * (1 + math.cos(math.pi * i / (len(iters)))) for i in iters])
schedule = np.concatenate((warmup_schedule, schedule))
assert len(schedule) == epochs * niter_per_ep
return schedule |