powerBestFitClass.php

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


class PHPExcel_Power_Best_Fit extends PHPExcel_Best_Fit
{
        protected $_bestFitType         = 'power';


        public function getValueOfYForX($xValue) {
                return $this->getIntersect() * pow(($xValue - $this->_Xoffset),$this->getSlope());
        }       //      function getValueOfYForX()


        public function getValueOfXForY($yValue) {
                return pow((($yValue + $this->_Yoffset) / $this->getIntersect()),(1 / $this->getSlope()));
        }       //      function getValueOfXForY()


        public function getEquation($dp=0) {
                $slope = $this->getSlope($dp);
                $intersect = $this->getIntersect($dp);

                return 'Y = '.$intersect.' * X^'.$slope;
        }       //      function getEquation()


        public function getIntersect($dp=0) {
                if ($dp != 0) {
                        return round(exp($this->_intersect),$dp);
                }
                return exp($this->_intersect);
        }       //      function getIntersect()


        private function _power_regression($yValues, $xValues, $const) {
                foreach($xValues as &$value) {
                        if ($value < 0.0) {
                                $value = 0 - log(abs($value));
                        } elseif ($value > 0.0) {
                                $value = log($value);
                        }
                }
                unset($value);
                foreach($yValues 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);
        }       //      function _power_regression()


        function __construct($yValues, $xValues=array(), $const=True) {
                if (parent::__construct($yValues, $xValues) !== False) {
                        $this->_power_regression($yValues, $xValues, $const);
                }
        }       //      function __construct()

}       //      class powerBestFit