protected function calculate()
    {
        $method = $this->getMethod();
        $start = clone($this->start);
        $this->end = $start->$method($this->interval_count);
    }
protected function calculate()
    {
        $method = $this->getMethod();
        $start = clone($this->start);
        $this->end = $start->$method($this->interval_count);
    }
protected function calculate ( ) { $ method = $ this -> getMethod ( ) ; $ start = clone ( $ this -> start ) ; $ this -> end = $ start -> $ method ( $ this -> interval_count ) ; }
Calculate the end date of the period.

@return void
Calculate the end date of the period .