/**
* XNPV
*
* Returns the net present value for a schedule of cash flows that is not necessarily periodic.
* To calculate the net present value for a series of cash flows that is periodic, use the NPV function.
*
* Excel Function:
* =XNPV(rate,values,dates)
*
* @param float $rate The discount rate to apply to the cash flows.
* @param array of float $values A series of cash flows that corresponds to a schedule of payments in dates.
* The first payment is optional and corresponds to a cost or payment that occurs at the beginning of the investment.
* If the first value is a cost or payment, it must be a negative value. All succeeding payments are discounted based on a 365-day year.
* The series of values must contain at least one positive value and one negative value.
* @param array of mixed $dates A schedule of payment dates that corresponds to the cash flow payments.
* The first payment date indicates the beginning of the schedule of payments.
* All other dates must be later than this date, but they may occur in any order.
* @return float
*/
public static function XNPV($rate, $values, $dates)
{
$rate = Functions::flattenSingleValue($rate);
if (!is_numeric($rate)) {
return Functions::VALUE();
}
if (!is_array($values) || !is_array($dates)) {
return Functions::VALUE();
}
$values = Functions::flattenArray($values);
$dates = Functions::flattenArray($dates);
$valCount = count($values);
if ($valCount != count($dates)) {
return Functions::NAN();
}
if (min($values) > 0 || max($values) < 0) {
return Functions::VALUE();
}
$xnpv = 0.0;
for ($i = 0; $i < $valCount; ++$i) {
if (!is_numeric($values[$i])) {
return Functions::VALUE();
}
$xnpv += $values[$i] / pow(1 + $rate, DateTime::DATEDIF($dates[0], $dates[$i], 'd') / 365);
}
return is_finite($xnpv) ? $xnpv : Functions::VALUE();
}
