def adjust_learning_rate(optimizer, decay=0.1):
    """Sets the learning rate to the initial LR decayed by 0.5 every 20 epochs"""
    for param_group in optimizer.param_groups:
        param_group['lr'] = decay * param_group['lr']
Sets the learning rate to the initial LR decayed by 0.5 every 20 epochs
lib/model/utils/net_utils.py