GRU same configurations but in two different ways

问题:

I would like to do some sequence prediction in tensorflow using GRU. so I have created the same model in 2 different ways as follows:

In model 1 I have a 2 GRUs, one after the other, that is, the new_state1, the final hidden state of the first GRU, acts as the initial state to the second GRU. Therefore, the model outputs new_state1 and new_state2 consequentially. Note that this is not a 2 layer model, but only 1 layer. From the code below, I divided the input and the output into 2 parts where GRU1 takes the first part, and the second GRU takes the second part.

Also the random_seed is set and fixed for both model so that results can be comparable.

Model 1

import tensorflow as tf
import numpy as np

cell_size = 32

seq_length = 1000

time_steps1 = 500
time_steps2 = seq_length - time_steps1

x_t = np.arange(1, seq_length + 1)    
x_t_plus_1 = np.arange(2, seq_length + 2)

tf.set_random_seed(123)

m_dtype = tf.float32

input_1 = tf.placeholder(dtype=m_dtype, shape=[None, time_steps1, 1], name="input_1")
input_2 = tf.placeholder(dtype=m_dtype, shape=[None, time_steps2, 1], name="input_2")

labels1 = tf.placeholder(dtype=m_dtype, shape=[None, time_steps1, 1], name="labels_1")
labels2 = tf.placeholder(dtype=m_dtype, shape=[None, time_steps2, 1], name="labels_2")

labels = tf.concat([labels1, labels2], axis=1, name="labels")

initial_state = tf.placeholder(shape=[None, cell_size], dtype=m_dtype, name="initial_state")

def model(input_feat1, input_feat2):
    with tf.variable_scope("GRU"):
        cell1 = tf.nn.rnn_cell.GRUCell(cell_size)
        cell2 = tf.nn.rnn_cell.GRUCell(cell_size)

        with tf.variable_scope("First50"):
            # output1: shape=[1, time_steps1, 32]
            output1, new_state1 = tf.nn.dynamic_rnn(cell1, input_feat1, dtype=m_dtype, initial_state=initial_state)

        with tf.variable_scope("Second50"):
            # output2: shape=[1, time_steps2, 32]
            output2, new_state2 = tf.nn.dynamic_rnn(cell2, input_feat2, dtype=m_dtype, initial_state=new_state1)

        with tf.variable_scope("output"):
            # output shape: [1, time_steps1 + time_steps2, 32] => [1, 100, 32]
            output = tf.concat([output1, output2], axis=1)

            output = tf.reshape(output, shape=[-1, cell_size])
            output = tf.layers.dense(output, units=1)
            output = tf.reshape(output, shape=[1, time_steps1 + time_steps2, 1])

        with tf.variable_scope("outputs_1_2_reshaped"):
            output1 = tf.slice(input_=output, begin=[0, 0, 0], size=[-1, time_steps1, -1])
            output2 = tf.slice(input_=output, begin=[0, time_steps1, 0], size=[-1, time_steps2, 1])

            print(output.get_shape().as_list(), "1")
            print(output1.get_shape().as_list(), "2")
            print(output2.get_shape().as_list(), "3")

            return output, output1, output2, initial_state, new_state1, new_state2

output, output1, output2, initial_state, new_state1, new_state2 = model(input_1, input_2)

init = tf.global_variables_initializer()

with tf.Session() as sess:
    sess.run(init)

    to_run_list = [new_state1, new_state2]

    in1 = np.reshape(x_t[:time_steps1], newshape=(1, time_steps1, 1))
    in2 = np.reshape(x_t[time_steps1:], newshape=(1, time_steps2, 1))
    l1 = np.reshape(x_t_plus_1[:time_steps1], newshape=(1, time_steps1, 1))
    l2 = np.reshape(x_t_plus_1[time_steps1:], newshape=(1, time_steps2, 1))
    i_s = np.zeros([1, cell_size])

    new_s1, new_s2 = sess.run(to_run_list, feed_dict={input_1: in1,
                                                              input_2: in2,
                                                              labels1: l1,
                                                              labels2: l2,
                                                              initial_state: i_s})

    print(np.shape(new_s1), np.shape(new_s2))

    print(np.mean(new_s1), np.mean(new_s2))
    print(np.sum(new_s1), np.sum(new_s2))

In this model, Instead of having 2 different GRU, I created one, and I divided the input and labels into 2 different parts as well, and I used a for loop to iterate over my input dataset. Then the final state is taken and fed back into the same model as initial state.

Note that both model1 and model2 have the very first initial state of zeros.

Model 2

import tensorflow as tf
import numpy as np

cell_size = 32

seq_length = 1000

time_steps = 500

x_t = np.arange(1, seq_length + 1)    
x_t_plus_1 = np.arange(2, seq_length + 2)

tf.set_random_seed(123)

m_dtype = tf.float32

inputs = tf.placeholder(dtype=m_dtype, shape=[None, time_steps, 1], name="inputs")

labels = tf.placeholder(dtype=m_dtype, shape=[None, time_steps, 1], name="labels")

initial_state = tf.placeholder(shape=[None, cell_size], dtype=m_dtype, name="initial_state")

grads_initial_state = tf.placeholder(dtype=m_dtype, shape=[None, cell_size], name="prev_grads")

this_is_last_batch = tf.placeholder(dtype=tf.bool, name="this_is_last_batch")

def model(input_feat):
    with tf.variable_scope("GRU"):
        cell = tf.nn.rnn_cell.GRUCell(cell_size)

        with tf.variable_scope("cell"):
            # output1: shape=[1, time_steps, 32]
            output, new_state = tf.nn.dynamic_rnn(cell, input_feat, dtype=m_dtype, initial_state=initial_state)

        with tf.variable_scope("output"):

            output = tf.reshape(output, shape=[-1, cell_size])
            output = tf.layers.dense(output, units=1)
            output = tf.reshape(output, shape=[1, time_steps, 1])

            print(output.get_shape().as_list(), "1")

            return output, new_state

output, new_state = model(inputs)

init = tf.global_variables_initializer()

with tf.Session() as sess:
    sess.run(init)

    # 1000 // 500 = 2
    num_iterations = seq_length // time_steps
    print("num_iterations:", num_iterations)

    final_states = []
    to_run_list = [grads_wrt_initial_state, new_state]

    for i in range(num_iterations):

        current_xt = x_t[i * time_steps: (i + 1)*time_steps]
        current_xt_plus_1 = x_t_plus_1[i*time_steps: (i + 1)*time_steps]

        in1 = np.reshape(current_xt, newshape=(1, time_steps, 1))
        l1 = np.reshape(current_xt_plus_1, newshape=(1, time_steps, 1))
        i_s = np.zeros([1, cell_size])

        if i == 0:
            new_s = sess.run(new_state, feed_dict={inputs: in1,
                                                   labels: l1,
                                                   initial_state: i_s})
            final_states.append(new_s)
            print("---->", np.mean(final_states[-1]), np.sum(final_states[-1]), i)
        else:
            new_s = sess.run(new_state, feed_dict={inputs: in1,
                                                   labels: l1,
                                                   initial_state: final_states[-1]})
            final_states.append(new_s)
            print("---->", np.mean(final_states[-1]), np.sum(final_states[-1]), i)

Finally, after printing out the statistics of new_state1 and new_state2 in model1, they were different from the new_state, after each iteration, in model2.

I would like to know how to fix this problem and why is that happening.

Edit:

I have figured out that the weights values of the gru in both files are different

Now how can I reproduce the same results in 2 the different files even after setting the random seed?

Any help is much appreciated!!!

回答1:

so to reproduce the same results in different files, tf.set_random_seed() is not enough. I figured out that we need to also set the seed for the intializers of the gru cells as well as the initializers of the weights in the dense layer at the output (this is at least acccording to my model); so the definition of the cell is now:

cell1 = tf.nn.rnn_cell.GRUCell(cell_size, kernel_initializer=tf.glorot_normal_initializer(seed=123, dtype=m_dtype))

And for the dense layer:

output = tf.layers.dense(output, units=1, kernel_initializer=tf.glorot_uniform_initializer(seed=123, dtype=m_dtype))

Note that any other initializer could be used as long as we set the seed the dtype for it.