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

/**
 * PHPExcel_Logarithmic_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_Logarithmic_Best_Fit extends PHPExcel_Best_Fit
{
  /**
   * Algorithm type to use for best-fit
   * (Name of this trend class)
   *
   * @var string
   *
   */
  protected $bestFitType = 'logarithmic';
  
  /**
   * 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 () + $this->getSlope () * log ( $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 exp ( ($yValue - $this->getIntersect ()) / $this->getSlope () );
  }
  
  /**
   * Return the Equation of the best-fit line
   *
   * @param int $dp
   *          Number of places of decimal precision to display
   * @return string
   *
   */
  public function getEquation($dp = 0)
  {
    $slope = $this->getSlope ( $dp );
    $intersect = $this->getIntersect ( $dp );
    
    return 'Y = ' . $intersect . ' + ' . $slope . ' * log(X)';
  }
  
  /**
   * Execute the regression and calculate the goodness of fit for a set of X and Y data values
   *
   * @param float[] $yValues
   *          The set of Y-values for this regression
   * @param float[] $xValues
   *          The set of X-values for this regression
   * @param boolean $const          
   */
  private function logarithmicRegression($yValues, $xValues, $const)
  {
    foreach ( $xValues as &$value )
    {
      if ($value < 0.0)
      {
        $value = 0 - log ( abs ( $value ) );
      }
      elseif ($value > 0.0)
      {
        $value = log ( $value );
      }
    }
    unset ( $value );
    
    $this->leastSquareFit ( $yValues, $xValues, $const );
  }
  
  /**
   * Define the regression and calculate the goodness of fit for a set of X and Y data values
   *
   * @param float[] $yValues
   *          The set of Y-values for this regression
   * @param float[] $xValues
   *          The set of X-values for this regression
   * @param boolean $const          
   */
  public function __construct($yValues, $xValues = array(), $const = true)
  {
    if (parent::__construct ( $yValues, $xValues ) !== false)
    {
      $this->logarithmicRegression ( $yValues, $xValues, $const );
    }
  }
}
