# import related module
from tensorflow.python.framework import constant_op
from tensorflow.python.framework import ops
from tensorflow.python.ops import control_flow_ops
from tensorflow.python.ops import math_ops
# implementation of inv decay in caffe base_lr*（1+gamm*itear）^(-power)
def inv_decay(learning_rate, global_step, gamma, power, name=None):
    if global_step is None:
        raise ValueError("global_step is required for inv_decay.")
    with ops.name_scope(name, "InvDecay",
                      [learning_rate, global_step,
                       gamma, power]) as name:
        learning_rate = ops.convert_to_tensor(learning_rate, name="learning_rate")
        dtype = learning_rate.dtype
        global_step = math_ops.cast(global_step, dtype)
        gamma = math_ops.cast(gamma, dtype)
        power = math_ops.cast(power, dtype)
        base = math_ops.multiply(gamma, global_step)
        return math_ops.multiply(learning_rate, math_ops.pow(1+base, -power),
                                 name=name)
lr = inv_decay(learning_rate=0.0005, global_step=get_global_step_var()-2800000,
        gamma=0.0001,
        power=0.75)
tf.summary.scalar('lr', lr)
optimizer=tf.train.GradientDescentOptimizer(lr)