Exercise

Calculate the prime numbers between 0 and 100 by using a Boolean array.

Solution:

import numpy as np

is_prime = np.ones((100,), dtype=bool)

# Cross out 0 and 1 which are not primes:

is_prime[:2] = 0

# cross out its higher multiples (sieve of Eratosthenes):

nmax = int(np.sqrt(len(is_prime)))

for i in range(2, nmax):

is_prime[2*i::i] = False

print(np.nonzero(is_prime))