code: 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']);
      }
docs: 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