public function isConvergent ()
	{
		$is = true;
		for( $i=$this->interval->getStart(); $i<$this->interval->getEnd(); $i++ )
		{
			$an = $this->getPartialSum( $this->interval->getStart(), $i );
			$an1 = $this->getPartialSum( $this->interval->getStart(), $i+1 );
			$diff = abs( $an1 - $an );
//			echo "<br>an1: ".$an1." | an: ".$an." | diff: ".$diff;
			if (!$old_diff) $old_diff = $diff;
			else if( $diff >= $old_diff )
				$is = false;
		}
		return $is;
	}