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RATE Function
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| // Copyright (c) 2012 Sutoiku, Inc. (MIT License) | |
| function RATE(periods, payment, present, future, type, guess) { | |
| // Credits: rabugento | |
| // Initialize guess | |
| var guess = (typeof guess === 'undefined') ? 0.01 : guess; | |
| // Initialize future | |
| var future = (typeof future === 'undefined') ? 0 : future; | |
| // Initialize type | |
| var type = (typeof type === 'undefined') ? 0 : type; | |
| // Evaluate periods (TODO: replace with secure expression evaluator) | |
| periods = eval(periods); | |
| // Set maximum epsilon for end of iteration | |
| var epsMax = 1e-10; | |
| // Set maximum number of iterations | |
| var iterMax = 50; | |
| // 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 + nper * rate) + payment * (1 + rate * type) * nper + future; | |
| } else { | |
| f = Math.exp(nper * Math.log(1 + rate)); | |
| y = present * f + payment * (1 / rate + type) * (f - 1) + future; | |
| } | |
| y0 = present + payment * nper + 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 + nper * rate) + payment * (1 + rate * type) * nper + future; | |
| } else { | |
| f = Math.exp(nper * Math.log(1 + rate)); | |
| y = present * f + payment * (1 / rate + type) * (f - 1) + future; | |
| } | |
| y0 = y1; | |
| y1 = y; | |
| ++i; | |
| } | |
| return rate; | |
| } |
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