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<?php
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namespace PhpOffice\PhpSpreadsheet\Shared\Trend;
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class Trend
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{
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    const TREND_LINEAR = 'Linear';
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    const TREND_LOGARITHMIC = 'Logarithmic';
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    const TREND_EXPONENTIAL = 'Exponential';
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    const TREND_POWER = 'Power';
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    const TREND_POLYNOMIAL_2 = 'Polynomial_2';
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    const TREND_POLYNOMIAL_3 = 'Polynomial_3';
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    const TREND_POLYNOMIAL_4 = 'Polynomial_4';
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    const TREND_POLYNOMIAL_5 = 'Polynomial_5';
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    const TREND_POLYNOMIAL_6 = 'Polynomial_6';
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    const TREND_BEST_FIT = 'Bestfit';
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    const TREND_BEST_FIT_NO_POLY = 'Bestfit_no_Polynomials';
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    /**
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     * Names of the best-fit Trend analysis methods.
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     *
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     * @var string[]
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     */
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    private static $trendTypes = [
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        self::TREND_LINEAR,
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        self::TREND_LOGARITHMIC,
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        self::TREND_EXPONENTIAL,
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        self::TREND_POWER,
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    ];
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    /**
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     * Names of the best-fit Trend polynomial orders.
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     *
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     * @var string[]
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     */
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    private static $trendTypePolynomialOrders = [
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        self::TREND_POLYNOMIAL_2,
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        self::TREND_POLYNOMIAL_3,
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        self::TREND_POLYNOMIAL_4,
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        self::TREND_POLYNOMIAL_5,
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        self::TREND_POLYNOMIAL_6,
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    ];
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    /**
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     * Cached results for each method when trying to identify which provides the best fit.
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     *
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     * @var BestFit[]
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     */
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    private static $trendCache = [];
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    /**
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     * @param string $trendType
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     * @param array $yValues
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     * @param array $xValues
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     * @param bool $const
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     *
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     * @return mixed
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     */
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    public static function calculate($trendType = self::TREND_BEST_FIT, $yValues = [], $xValues = [], $const = true)
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    {
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        //    Calculate number of points in each dataset
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        $nY = count($yValues);
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        $nX = count($xValues);
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        //    Define X Values if necessary
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        if ($nX === 0) {
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            $xValues = range(1, $nY);
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        } elseif ($nY !== $nX) {
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            //    Ensure both arrays of points are the same size
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            trigger_error('Trend(): Number of elements in coordinate arrays do not match.', E_USER_ERROR);
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        }
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        $key = md5($trendType . $const . serialize($yValues) . serialize($xValues));
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        //    Determine which Trend method has been requested
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        switch ($trendType) {
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            //    Instantiate and return the class for the requested Trend method
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            case self::TREND_LINEAR:
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            case self::TREND_LOGARITHMIC:
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            case self::TREND_EXPONENTIAL:
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            case self::TREND_POWER:
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                if (!isset(self::$trendCache[$key])) {
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                    $className = '\PhpOffice\PhpSpreadsheet\Shared\Trend\\' . $trendType . 'BestFit';
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                    self::$trendCache[$key] = new $className($yValues, $xValues, $const);
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                }
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                return self::$trendCache[$key];
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            case self::TREND_POLYNOMIAL_2:
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            case self::TREND_POLYNOMIAL_3:
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            case self::TREND_POLYNOMIAL_4:
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            case self::TREND_POLYNOMIAL_5:
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            case self::TREND_POLYNOMIAL_6:
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                if (!isset(self::$trendCache[$key])) {
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                    $order = (int) substr($trendType, -1);
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                    self::$trendCache[$key] = new PolynomialBestFit($order, $yValues, $xValues);
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                }
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                return self::$trendCache[$key];
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            case self::TREND_BEST_FIT:
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            case self::TREND_BEST_FIT_NO_POLY:
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                //    If the request is to determine the best fit regression, then we test each Trend line in turn
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                //    Start by generating an instance of each available Trend method
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                $bestFit = [];
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                $bestFitValue = [];
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                foreach (self::$trendTypes as $trendMethod) {
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                    $className = '\PhpOffice\PhpSpreadsheet\Shared\Trend\\' . $trendType . 'BestFit';
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                    //* @phpstan-ignore-next-line
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                    $bestFit[$trendMethod] = new $className($yValues, $xValues, $const);
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                    $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
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                }
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                if ($trendType != self::TREND_BEST_FIT_NO_POLY) {
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                    foreach (self::$trendTypePolynomialOrders as $trendMethod) {
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                        $order = (int) substr($trendMethod, -1);
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                        $bestFit[$trendMethod] = new PolynomialBestFit($order, $yValues, $xValues);
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                        if ($bestFit[$trendMethod]->getError()) {
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                            unset($bestFit[$trendMethod]);
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                        } else {
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                            $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
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                        }
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                    }
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                }
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                //    Determine which of our Trend lines is the best fit, and then we return the instance of that Trend class
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                arsort($bestFitValue);
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                $bestFitType = key($bestFitValue);
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                return $bestFit[$bestFitType];
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            default:
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                return false;
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        }
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    }
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}