Multi tool use

tf.gather_nd is really slow when used for many times

I would like a loss function in tensorflow which is a complex combination of many elements. For example, this code:

import tensorflow as tf
import numpy as np
import time

input_layer = tf.placeholder(tf.float64, shape=[64,4])
output_layer = input_layer + 0.5*tf.tanh(tf.Variable(tf.random_uniform(shape=[64,4],
minval=-1,maxval=1,dtype=tf.float64)))

# random_combination is 2-d numpy array of the form:
# [[32, 34, 23, 56],[23,54,33,21],...]
random_combination = np.random.randint(64, size=(210000000, 4))

# a collector to collect the values
collector=

print('start looping')
print(time.asctime(time.localtime(time.time())))

# loop through random_combination and pick the elements of output_layer
for i in range(len(random_combination)):
[i,j,k,l] = [random_combination[i][0],random_combination[i][1],
random_combination[i][2],random_combination[i][3]]

# pick the needed element from output_layer
f1 = tf.gather_nd(output_layer,[i,0])
f2 = tf.gather_nd(output_layer,[i,2])
f3 = tf.gather_nd(output_layer,[i,3])
f4 = tf.gather_nd(output_layer,[i,4])

tf1 = f1+1
tf2 = f2+1
tf3 = f3+1
tf4 = f4+1
collector.append(0.3*tf.abs(f1*f2*tf3*tf4-tf1*tf2*f3*f4))

print('end looping')
print(time.asctime(time.localtime(time.time())))

# loss function
loss = tf.add_n(collector)


This takes around 50 minutes on my computer.
My question is that is it the proper way to do the coding in tensorflow?
Or there is a more time efficient way to index the elements?

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