public function buildPolynomial()
	{
		$t		= array();
		$a		= array();
		$keys	= array_keys( $this->data );
		$values	= array_values( $this->data );
		for( $i=0; $i<count( $keys ); $i++ )
		{
			$t[$i]	= $values[$i];
			for( $j=$i-1; $j>=0; $j-- )
				$t[$j]	= ( $t[$j+1] - $t[$j] ) / ( $keys[$i] - $keys[$j] );
			$a[$i]	= $t[0];
		}
		$this->polynomial	= $a;
	}