factorial.js

import { deepMap } from '../../utils/collection.js'
import { factory } from '../../utils/factory.js'

const name = 'factorial'
const dependencies = ['typed', 'isInteger', 'gamma']

export const createFactorial = /* #__PURE__ */ factory(name, dependencies, ({
  typed, isInteger, bignumber, gamma
}) => {
  /**
   * Compute the factorial of a value
   *
   * Factorial only supports an integer value as argument.
   * For matrices, the function is evaluated element wise.
   *
   * Syntax:
   *
   *    math.factorial(n)
   *
   * Examples:
   *
   *    math.factorial(5)    // returns 120
   *    math.factorial(3)    // returns 6
   *
   * See also:
   *
   *    combinations, combinationsWithRep, gamma, permutations
   *
   * @param {number | BigNumber | Array | Matrix} n   An integer number
   * @return {number | BigNumber | Array | Matrix}    The factorial of `n`
   */
  return typed(name, {
    number: function (n) {
      if (n < 0) {
        throw new Error('Value must be non-negative')
      }

      return gamma(n + 1)
    },

    BigNumber: function (n) {
      if (n.isNegative()) {
        throw new Error('Value must be non-negative')
      }
      if (!n.isFinite()) return n
      if (!isInteger(n)) throw new Error('Value must be integer')

      return gamma(n.plus(1))
    },

    'Array | Matrix': typed.referToSelf(self => n => deepMap(n, self))
  })
})