sft_wick._util — Internal Utilities

Internal utility functions.

sft_wick._util.double_factorial(n)

Compute n!! = n * (n-2) * (n-4) * … * 1.

For odd n: n!! = 1 * 3 * 5 * … * n For even n: n!! = 2 * 4 * 6 * … * n 0!! = 1, (-1)!! = 1

Parameters:

n (int)

Return type:

int