mathjs/lib/function/statistics/prod.js

Math.js is an extensive math library for JavaScript and Node.js. It features a flexible expression parser with support for symbolic computation, comes with a large set of built-in functions and constants, and offers an integrated solution to work with dif

'use strict';

var deepForEach = require('../../utils/collection/deepForEach');

function factory (type, config, load, typed) {
  var multiply = load(require('../arithmetic/multiplyScalar'));
  var improveErrorMessage = load(require('./utils/improveErrorMessage'));

  /**
   * Compute the product of a matrix or a list with values.
   * In case of a (multi dimensional) array or matrix, the sum of all
   * elements will be calculated.
   *
   * Syntax:
   *
   *     math.prod(a, b, c, ...)
   *     math.prod(A)
   *
   * Examples:
   *
   *     math.multiply(2, 3);           // returns 6
   *     math.prod(2, 3);               // returns 6
   *     math.prod(2, 3, 4);            // returns 24
   *     math.prod([2, 3, 4]);          // returns 24
   *     math.prod([[2, 5], [4, 3]]);   // returns 120
   *
   * See also:
   *
   *    mean, median, min, max, sum, std, var
   *
   * @param {... *} args  A single matrix or or multiple scalar values
   * @return {*} The product of all values
   */
  var prod = typed('prod', {
    // prod([a, b, c, d, ...])
    'Array | Matrix': _prod,

    // prod([a, b, c, d, ...], dim)
    'Array | Matrix, number | BigNumber': function (array, dim) {
      // TODO: implement prod(A, dim)
      throw new Error('prod(A, dim) is not yet supported');
      //return reduce(arguments[0], arguments[1], math.prod);
    },

    // prod(a, b, c, d, ...)
    '...': function (args) {
      return _prod(args);
    }
  });

  prod.toTex = undefined; // use default template

  return prod;

  /**
   * Recursively calculate the product of an n-dimensional array
   * @param {Array} array
   * @return {number} prod
   * @private
   */
  function _prod(array) {
    var prod = undefined;

    deepForEach(array, function (value) {
      try {
        prod = (prod === undefined) ? value : multiply(prod, value);
      }
      catch (err) {
        throw improveErrorMessage(err, 'prod', value);
      }
    });

    if (prod === undefined) {
      throw new Error('Cannot calculate prod of an empty array');
    }

    return prod;
  }
}

exports.name = 'prod';
exports.factory = factory;