vendor/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/Trend/Trend.php

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<?php

namespace PhpOffice\PhpSpreadsheet\Shared\Trend;

class Trend
{
    const TREND_LINEAR = 'Linear';
    const TREND_LOGARITHMIC = 'Logarithmic';
    const TREND_EXPONENTIAL = 'Exponential';
    const TREND_POWER = 'Power';
    const TREND_POLYNOMIAL_2 = 'Polynomial_2';
    const TREND_POLYNOMIAL_3 = 'Polynomial_3';
    const TREND_POLYNOMIAL_4 = 'Polynomial_4';
    const TREND_POLYNOMIAL_5 = 'Polynomial_5';
    const TREND_POLYNOMIAL_6 = 'Polynomial_6';
    const TREND_BEST_FIT = 'Bestfit';
    const TREND_BEST_FIT_NO_POLY = 'Bestfit_no_Polynomials';

    /**
     * Names of the best-fit Trend analysis methods.
     *
     * @var string[]
     */
    private static $trendTypes = [
        self::TREND_LINEAR,
        self::TREND_LOGARITHMIC,
        self::TREND_EXPONENTIAL,
        self::TREND_POWER,
    ];

    /**
     * Names of the best-fit Trend polynomial orders.
     *
     * @var string[]
     */
    private static $trendTypePolynomialOrders = [
        self::TREND_POLYNOMIAL_2,
        self::TREND_POLYNOMIAL_3,
        self::TREND_POLYNOMIAL_4,
        self::TREND_POLYNOMIAL_5,
        self::TREND_POLYNOMIAL_6,
    ];

    /**
     * Cached results for each method when trying to identify which provides the best fit.
     *
     * @var bestFit[]
     */
    private static $trendCache = [];

    public static function calculate($trendType = self::TREND_BEST_FIT, $yValues = [], $xValues = [], $const = true)
    {
        //    Calculate number of points in each dataset
        $nY = count($yValues);
        $nX = count($xValues);

        //    Define X Values if necessary
        if ($nX == 0) {
            $xValues = range(1, $nY);
            $nX = $nY;