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 eight. To do that, 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]

What just happened?

We used the prod and cumprod functions to calculate factorials (see ndarraymethods.py).

import numpy as np

a = np.arange(5)
print "a =", a
print "Clipped", a.clip(1, 2)

a = np.arange(4)
print a
print "Compressed", a.compress(a > 2)

b = np...