# Computation :: Probability

- combination(set,subset)
- Returns the number of unique subsets created from all combinations of a number of elements, or (-1) on error.

- erf(x)
- Returns the value of erf(x), the "error function" or cumulative distribution function, which computes the probability that a Gaussian random number falls within a given range.

- exp_dist(mean)
- Returns a random number with exponential distribution.

- factorial(number)
- Returns the factorial of a given number.

- gauss(mean,deviation)
- Returns a pseudo-random number with an exact Gaussian distribution.

- permutation(set,subset)
- Returns the number of unique subsets created from all permutations of a number of elements in which the order of the chosen elements is significant, or (-1) on error.

- random_weighted(p0 [, p1, ..., pN])
- Returns a randomly selected index based on their given relative probabilities.

- roll_dice(num,sides)
- Returns the sum of a number of die rolls using dice with a given number of sides.