Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Financial.php
public static function SYD($cost, $salvage, $life, $period)
    {
        $cost = Functions::flattenSingleValue($cost);
        $salvage = Functions::flattenSingleValue($salvage);
        $life = Functions::flattenSingleValue($life);
        $period = Functions::flattenSingleValue($period);

        // Calculate
        if ((is_numeric($cost)) && (is_numeric($salvage)) && (is_numeric($life)) && (is_numeric($period))) {
            if (($life < 1) || ($period > $life)) {
                return Functions::NAN();
            }

            return (($cost - $salvage) * ($life - $period + 1) * 2) / ($life * ($life + 1));
        }

        return Functions::VALUE();
    }
public static function SYD($cost, $salvage, $life, $period)
    {
        $cost = Functions::flattenSingleValue($cost);
        $salvage = Functions::flattenSingleValue($salvage);
        $life = Functions::flattenSingleValue($life);
        $period = Functions::flattenSingleValue($period);

        // Calculate
        if ((is_numeric($cost)) && (is_numeric($salvage)) && (is_numeric($life)) && (is_numeric($period))) {
            if (($life < 1) || ($period > $life)) {
                return Functions::NAN();
            }

            return (($cost - $salvage) * ($life - $period + 1) * 2) / ($life * ($life + 1));
        }

        return Functions::VALUE();
    }
SYD.

Returns the sum-of-years' digits depreciation of an asset for a specified period.

@param mixed $cost Initial cost of the asset
@param mixed $salvage Value at the end of the depreciation
@param mixed $life Number of periods over which the asset is depreciated
@param mixed $period Period

@return float