Excel RATE() Javascript Function

Finance.excel.rate.js

/*!
 * @fileOverview Finance Excel Rate Formula Javascript Equivalent
 * @version 1.0.0
 *
 * @author Burak Arslan @kucukharf http://www.github.com/kucukharf
 * @license
 * Copyright (c) 2010-2018 Burak Arslan
 * Licensed under Creative Commons (CC) license
 * @usage RATE($periods, $payment, $present, $future, $type, $guess)
 */

RATE = function(periods, payment, present, future, type, guess) {
    guess = (guess === undefined) ? 0.01 : guess;
    future = (future === undefined) ? 0 : future;
    type = (type === undefined) ? 0 : type;
  
    // Set maximum epsilon for end of iteration
    var epsMax = 1e-10;
  
    // Set maximum number of iterations
    var iterMax = 10;
  
    // Implement Newton's method
    var y, y0, y1, x0, x1 = 0,
      f = 0,
      i = 0;
    var rate = guess;
    if (Math.abs(rate) < epsMax) {
      y = present * (1 + periods * rate) + payment * (1 + rate * type) * periods + future;
    } else {
      f = Math.exp(periods * Math.log(1 + rate));
      y = present * f + payment * (1 / rate + type) * (f - 1) + future;
    }
    y0 = present + payment * periods + future;
    y1 = present * f + payment * (1 / rate + type) * (f - 1) + future;
    i = x0 = 0;
    x1 = rate;
    while ((Math.abs(y0 - y1) > epsMax) && (i < iterMax)) {
      rate = (y1 * x0 - y0 * x1) / (y1 - y0);
      x0 = x1;
      x1 = rate;
        if (Math.abs(rate) < epsMax) {
          y = present * (1 + periods * rate) + payment * (1 + rate * type) * periods + future;
        } else {
          f = Math.exp(periods * Math.log(1 + rate));
          y = present * f + payment * (1 / rate + type) * (f - 1) + future;
        }
      y0 = y1;
      y1 = y;
      ++i;
    }
    return rate;
};