javascript数租

function IRR(cashFlows, estimatedResult) {
var result = "isNAN";
if (cashFlows != null && cashFlows.length > 0) {
// check if business startup costs is not zero:
if (cashFlows[0] != 0) {
var noOfCashFlows = cashFlows.length;
var sumCashFlows = 0;
// check if at least 1 positive and 1 negative cash flow exists:
var noOfNegativeCashFlows = 0;
var noOfPositiveCashFlows = 0;
for (var i = 0; i < noOfCashFlows; i++) {
sumCashFlows += cashFlows[i];
if (cashFlows[i] > 0) {
noOfPositiveCashFlows++;
} else {
if (cashFlows[i] < 0) {
noOfNegativeCashFlows++;
}
}
}

// at least 1 negative and 1 positive cash flow available?
if (noOfNegativeCashFlows > 0 && noOfPositiveCashFlows > 0) {
// set estimated result:
var irrGuess = 0.1; // default: 10%
if (!isNaN(estimatedResult)) {
irrGuess = estimatedResult;
if (irrGuess <= 0) {
irrGuess = 0.5;
}
}

// initialize first IRR with estimated result:
var irr = 0;
if (sumCashFlows < 0) { // sum of cash flows negative?
irr = -irrGuess;
} else { // sum of cash flows not negative
irr = irrGuess;
}

// iteration:
// the smaller the distance, the smaller the interpolation
// error
var minDistance = 1e-15;

// business startup costs
var cashFlowStart = cashFlows[0];
var maxIteration = 100;
var wasHi = false;
var cashValue = 0;
for (var i = 0; i <= maxIteration; i++) {
// calculate cash value with current irr:
cashValue = cashFlowStart; // init with startup costs

// for each cash flow
for (var j = 1; j < noOfCashFlows; j++) {
cashValue += cashFlows[j] / Math.pow(1 + irr, j);
}

// cash value is nearly zero
if (Math.abs(cashValue) < 0.01) {
result = irr;
break;
}

// adjust irr for next iteration:
// cash value > 0 => next irr > current irr
if (cashValue > 0) {
if (wasHi) {
irrGuess /= 2;
}
irr += irrGuess;
if (wasHi) {
irrGuess -= minDistance;
wasHi = false;
}
} else {// cash value < 0 => next irr < current irr
irrGuess /= 2;
irr -= irrGuess;
wasHi = true;
}

// estimated result too small to continue => end
// calculation
if (irrGuess <= minDistance) {
result = irr;
break;
}
}
}
}
}
return result;
}