/**
* Returns the internal rate of return of a cash flow series, considering both financial and reinvestment rates
* Excel equivalent: MIRR
*
* @param array Cash flow series
* @param float Interest rate on the money used in the cash flow
* @param float Interest rate received when reinvested
* @return float
* @static
* @access public
*/
function modifiedInternalRateOfReturn($values, $finance_rate, $reinvest_rate)
{
if (!is_array($values)) {
return PEAR::raiseError('The cash flow series most be an array');
}
if (min($values) * max($values) >= 0) {
return PEAR::raiseError('Cash flow must contain at least one positive value and one negative value');
}
$positive_flows = $negative_flows = array();
foreach ($values as $value) {
if ($value >= 0) {
$positive_flows[] = $value;
$negative_flows[] = 0;
} else {
$positive_flows[] = 0;
$negative_flows[] = $value;
}
}
$nper = count($values);
return pow(-Math_Finance::netPresentValue($reinvest_rate, $positive_flows) * pow(1 + $reinvest_rate, $nper) / Math_Finance::netPresentValue($finance_rate, $negative_flows) / (1 + $finance_rate), 1 / ($nper - 1)) - 1;
}
function testnetPresentValue()
{
// various random calculations
$this->assertTrue(abs(1188.443412 - Math_Finance::netPresentValue(0.1, array(-10000, 3000, 4200, 6800))) < FINANCE_PRECISION);
// cash flow series must be an array
$this->assertType('object', Math_Finance::netPresentValue(0.1, -1000, 3000, 4200, 6800));
}
