Issue
I am new to tensorflow, I am trying to find a function that calculates the n!. I saw that one can use the gamma function, which was possible with theano, but did not work for tensorflow.
factorial = theano.tensor.gamma(v)
I am using a for loop to multiply number from n to 1, but I assume there is an easier and faster way. I saw functions related to gamma distribution, but couldn't figure out how to calculate the factorial. Would appreciate if one can point me to some documentation.
Here is the way I do it now
import tensorflow as tf
factorial = tf.Variable(1, "factorial")
recursion = tf.Variable(1, "recursion")
# calculate factorial
mult = tf.multiply(recursion, factorial)
assign_fact = tf.assign(factorial, mult)
init = tf.global_variables_initializer()
with tf.Session() as sess:
sess.run(init)
for i in range(2,10):
counter = tf.assign(recursion, tf.constant(i))
sess.run(counter)
sess.run(assign_fact)
print(i,"factorial is", sess.run(factorial))
sess.close()
Output is
2 factorial is 2
3 factorial is 6
4 factorial is 24
5 factorial is 120
6 factorial is 720
7 factorial is 5040
8 factorial is 40320
9 factorial is 362880
Solution
Try this: tf.exp(tf.lgamma(x + 1))
.
tf.lgamma
computes the log of the absolute value of Gamma(x) element-wise, so the exponent will give you the raw Gamma(x) value:
>>> sess.run(tf.exp(tf.lgamma(5.0)))
24.0
Answered By - Maxim
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