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<?php
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/**
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 * PHPExcel
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 *
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 * Copyright (c) 2006 - 2013 PHPExcel
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 *
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 * This library is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * This library is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with this library; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
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 *
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 * @category   PHPExcel
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 * @package    PHPExcel_Shared_Trend
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 * @copyright  Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
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 * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt	LGPL
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 * @version    ##VERSION##, ##DATE##
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 */
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require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/bestFitClass.php';
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/**
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 * PHPExcel_Power_Best_Fit
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 *
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 * @category   PHPExcel
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 * @package    PHPExcel_Shared_Trend
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 * @copyright  Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
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 */
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class PHPExcel_Power_Best_Fit extends PHPExcel_Best_Fit
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{
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	/**
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	 * Algorithm type to use for best-fit
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	 * (Name of this trend class)
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	 *
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	 * @var	string
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	 **/
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	protected $_bestFitType		= 'power';
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	/**
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	 * Return the Y-Value for a specified value of X
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	 *
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	 * @param	 float		$xValue			X-Value
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	 * @return	 float						Y-Value
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	 **/
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	public function getValueOfYForX($xValue) {
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		return $this->getIntersect() * pow(($xValue - $this->_Xoffset),$this->getSlope());
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	}	//	function getValueOfYForX()
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	/**
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	 * Return the X-Value for a specified value of Y
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	 *
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	 * @param	 float		$yValue			Y-Value
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	 * @return	 float						X-Value
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	 **/
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	public function getValueOfXForY($yValue) {
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		return pow((($yValue + $this->_Yoffset) / $this->getIntersect()),(1 / $this->getSlope()));
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	}	//	function getValueOfXForY()
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	/**
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	 * Return the Equation of the best-fit line
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	 *
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	 * @param	 int		$dp		Number of places of decimal precision to display
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	 * @return	 string
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	 **/
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	public function getEquation($dp=0) {
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		$slope = $this->getSlope($dp);
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		$intersect = $this->getIntersect($dp);
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		return 'Y = '.$intersect.' * X^'.$slope;
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	}	//	function getEquation()
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	/**
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	 * Return the Value of X where it intersects Y = 0
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	 *
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	 * @param	 int		$dp		Number of places of decimal precision to display
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	 * @return	 string
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	 **/
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	public function getIntersect($dp=0) {
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		if ($dp != 0) {
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			return round(exp($this->_intersect),$dp);
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		}
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		return exp($this->_intersect);
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	}	//	function getIntersect()
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	/**
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	 * Execute the regression and calculate the goodness of fit for a set of X and Y data values
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	 *
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	 * @param	 float[]	$yValues	The set of Y-values for this regression
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	 * @param	 float[]	$xValues	The set of X-values for this regression
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	 * @param	 boolean	$const
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	 */
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	private function _power_regression($yValues, $xValues, $const) {
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		foreach($xValues as &$value) {
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			if ($value < 0.0) {
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				$value = 0 - log(abs($value));
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			} elseif ($value > 0.0) {
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				$value = log($value);
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			}
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		}
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		unset($value);
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		foreach($yValues as &$value) {
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			if ($value < 0.0) {
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				$value = 0 - log(abs($value));
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			} elseif ($value > 0.0) {
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				$value = log($value);
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			}
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		}
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		unset($value);
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		$this->_leastSquareFit($yValues, $xValues, $const);
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	}	//	function _power_regression()
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	/**
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	 * Define the regression and calculate the goodness of fit for a set of X and Y data values
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	 *
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	 * @param	 float[]	$yValues	The set of Y-values for this regression
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	 * @param	 float[]	$xValues	The set of X-values for this regression
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	 * @param	 boolean	$const
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	 */
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	function __construct($yValues, $xValues=array(), $const=True) {
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		if (parent::__construct($yValues, $xValues) !== False) {
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			$this->_power_regression($yValues, $xValues, $const);
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		}
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	}	//	function __construct()
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}	//	class powerBestFit