Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Engineering.php
public static function IMLN($complexNumber)
    {
        $complexNumber = Functions::flattenSingleValue($complexNumber);

        $parsedComplex = self::parseComplex($complexNumber);

        if (($parsedComplex['real'] == 0.0) && ($parsedComplex['imaginary'] == 0.0)) {
            return Functions::NAN();
        }

        $logR = log(sqrt(($parsedComplex['real'] * $parsedComplex['real']) + ($parsedComplex['imaginary'] * $parsedComplex['imaginary'])));
        $t = self::IMARGUMENT($complexNumber);

        if ($parsedComplex['suffix'] == '') {
            return self::COMPLEX($logR, $t);
        }

        return self::COMPLEX($logR, $t, $parsedComplex['suffix']);
    }
public static function IMLN($complexNumber)
    {
        $complexNumber = Functions::flattenSingleValue($complexNumber);

        $parsedComplex = self::parseComplex($complexNumber);

        if (($parsedComplex['real'] == 0.0) && ($parsedComplex['imaginary'] == 0.0)) {
            return Functions::NAN();
        }

        $logR = log(sqrt(($parsedComplex['real'] * $parsedComplex['real']) + ($parsedComplex['imaginary'] * $parsedComplex['imaginary'])));
        $t = self::IMARGUMENT($complexNumber);

        if ($parsedComplex['suffix'] == '') {
            return self::COMPLEX($logR, $t);
        }

        return self::COMPLEX($logR, $t, $parsedComplex['suffix']);
    }
IMLN.

Returns the natural logarithm of a complex number in x + yi or x + yj text format.

Excel Function:
IMLN(complexNumber)

@param string $complexNumber the complex number for which you want the natural logarithm

@return string