NumPy : Beginner's Guide - Third Edition

Time for action – calculating the factorial

The ndarray class has the prod() method, which computes the product of the elements in an array. Perform the following steps to calculate the factorial:

1. Calculate the factorial of 8. To do this, generate an array with values 1 to 8 and call the prod() function on it:

   b = np.arange(1, 9)
   print("b =", b)
   print("Factorial", b.prod())

   Check the result with your pocket calculator:

   b = [1 2 3 4 5 6 7 8]
   Factorial 40320
   

   This is nice, but what if we want to know all the factorials from 1 to 8?

2. No problem! Call the cumprod() method, which computes the cumulative product of an array:

   print("Factorials", b.cumprod())

   It's pocket calculator time again:

   Factorials [    1     2     6    24   120   720  5040 40320]
   

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