ThinkPHP/Library/Org/Util/PHPExcel/Shared/trend/exponentialBestFitClass.php

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<?php

require_once(PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/bestFitClass.php');

/**
 * PHPExcel_Exponential_Best_Fit
 *
 * Copyright (c) 2006 - 2015 PHPExcel
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * @category   PHPExcel
 * @package    PHPExcel_Shared_Trend
 * @copyright  Copyright (c) 2006 - 2015 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt    LGPL
 * @version    ##VERSION##, ##DATE##
 */
class PHPExcel_Exponential_Best_Fit extends PHPExcel_Best_Fit
{
    /**
     * Algorithm type to use for best-fit
     * (Name of this trend class)
     *
     * @var    string
     **/
    protected $bestFitType        = 'exponential';

    /**
     * Return the Y-Value for a specified value of X
     *
     * @param     float        $xValue            X-Value
     * @return     float                        Y-Value
     **/
    public function getValueOfYForX($xValue)
    {
        return $this->getIntersect() * pow($this->getSlope(), ($xValue - $this->xOffset));
    }

    /**
     * Return the X-Value for a specified value of Y
     *
     * @param     float        $yValue            Y-Value
     * @return     float                        X-Value
     **/
    public function getValueOfXForY($yValue)
    {
        return log(($yValue + $this->yOffset) / $this->getIntersect()) / log($this->getSlope());
    }