IRR formula for PHP

gistfile1.txt

<?php

class IRRHelper{

	//Adapted from Javascript version here: https://gist.github.com/ghalimi/4591338
	//
	// Copyright (c) 2012 Sutoiku, Inc. (MIT License)
 	//
	// Some algorithms have been ported from Apache OpenOffice:
	//	 
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	 * Licensed to the Apache Software Foundation (ASF) under one
	 * or more contributor license agreements.  See the NOTICE file
	 * distributed with this work for additional information
	 * regarding copyright ownership.  The ASF licenses this file
	 * to you under the Apache License, Version 2.0 (the
	 * "License"); you may not use this file except in compliance
	 * with the License.  You may obtain a copy of the License at
	 * 
	 *   http://www.apache.org/licenses/LICENSE-2.0
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	 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
	 * KIND, either express or implied.  See the License for the
	 * specific language governing permissions and limitations
	 * under the License.
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	public static function IRR($values, $guess=0.1) {
		// Credits: algorithm inspired by Apache OpenOffice

		// Initialize dates and check that values contains at least one positive value and one negative value
		$dates = array();
		$positive = false;
		$negative = false;
		foreach($values as $index=>$value){
			$dates[] = ($index===0) ? 0 : $dates[$index-1] + 365;
			if($values[$index] > 0) $positive = true;
			if($values[$index] < 0) $negative = true;
		}

		// Return error if values does not contain at least one positive value and one negative value
		if(!$positive || !$negative) return null;

		// Initialize guess and resultRate
		$resultRate = $guess;

		// Set maximum epsilon for end of iteration
		$epsMax = 0.0000000001;

		// Set maximum number of iterations
		$iterMax = 50;

		// Implement Newton's method
		$newRate;
		$epsRate;
		$resultValue;
		$iteration = 0;
		$contLoop = true;
		while($contLoop && (++$iteration < $iterMax)){
			$resultValue = self::irrResult($values, $dates, $resultRate);
			$newRate = $resultRate - $resultValue / self::irrResultDeriv($values, $dates, $resultRate);
			$epsRate = abs($newRate - $resultRate);
			$resultRate = $newRate;
			$contLoop = ($epsRate > $epsMax) && (abs($resultValue) > $epsMax);
		}

		if($contLoop) return null;

		// Return internal rate of return
		return $resultRate;
	}

	// Calculates the resulting amount
	public static function irrResult($values, $dates, $rate){
		$r = $rate + 1;
		$result = $values[0];
		for($i=1;$i<count($values);$i++){
			$result += $values[$i] / pow($r, ($dates[$i] - $dates[0]) / 365);
		}
		return $result;
	}

	// Calculates the first derivation
	public static function irrResultDeriv($values, $dates, $rate){
		$r = $rate + 1;
		$result = 0;
		for($i=1;$i<count($values);$i++){
			$frac = ($dates[$i] - $dates[0]) / 365;
			$result -= $frac * $values[$i] / pow($r, $frac + 1);
		}
		return $result;
	}
	
}

echo IRRHelper::IRR(array(-100,0,120));

The guess value is set way too high, as most investments have returns that are less than 0.100. The formula skips all guesses below that guess value. Try setting it at 0.000001 (1E-5)

For me self::irrResultDeriv($values, $dates, $resultRate); is generating 0 values which is causing {"error":"Division by zero"}.
Need Help.

i have same problem too, irrResultDeriv return 0 if only 2 value in array

Same problem (division by zero). If anyone has gotten it right, please share (even using some other function).