def lr_schedule(epoch):
    """
    Learning rate is scheduled to be reduced after 40, 60, 80, 90 epochs.
    """
    lr = 0.001
    if epoch > 90:
        lr *= 0.0005
    elif epoch > 60:
        lr *= 0.001
    elif epoch > 40:
        lr *= 0.01
    elif epoch > 20:
        lr *= 0.1
    print('Learning rate: ', lr)
    return lr
