code: public static function NOMINAL($effect_rate = 0, $npery = 0)
      {
          $effect_rate = Functions::flattenSingleValue($effect_rate);
          $npery = (int) Functions::flattenSingleValue($npery);
  
          // Validate parameters
          if ($effect_rate <= 0 || $npery < 1) {
              return Functions::NAN();
          }
  
          // Calculate
          return $npery * (pow($effect_rate + 1, 1 / $npery) - 1);
      }
docs: NOMINAL.
  
  Returns the nominal interest rate given the effective rate and the number of compounding payments per year.
  
  @param float $effect_rate Effective interest rate
  @param int $npery Number of compounding payments per year
  
  @return float