Resources/PhpOffice/PhpSpreadsheet/Calculation/Statistical/Distributions/Weibull.php

<?php

namespace PhpOffice\PhpSpreadsheet\Calculation\Statistical\Distributions;

use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
use PhpOffice\PhpSpreadsheet\Calculation\Exception;
use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;

class Weibull
{
    use ArrayEnabled;

    /**
     * WEIBULL.
     *
     * Returns the Weibull distribution. Use this distribution in reliability
     * analysis, such as calculating a device's mean time to failure.
     *
     * @param mixed $value Float value for the distribution
     *                      Or can be an array of values
     * @param mixed $alpha Float alpha Parameter
     *                      Or can be an array of values
     * @param mixed $beta Float beta Parameter
     *                      Or can be an array of values
     * @param mixed $cumulative Boolean value indicating if we want the cdf (true) or the pdf (false)
     *                      Or can be an array of values
     *
     * @return array|float|string (string if result is an error)
     *         If an array of numbers is passed as an argument, then the returned result will also be an array
     *            with the same dimensions
     */
    public static function distribution($value, $alpha, $beta, $cumulative)
    {
        if (\is_array($value) || \is_array($alpha) || \is_array($beta) || \is_array($cumulative)) {
            return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $alpha, $beta, $cumulative);
        }

        try {
            $value = DistributionValidations::validateFloat($value);
            $alpha = DistributionValidations::validateFloat($alpha);
            $beta = DistributionValidations::validateFloat($beta);
            $cumulative = DistributionValidations::validateBool($cumulative);
        } catch (Exception $e) {
            return $e->getMessage();
        }

        if (($value < 0) || ($alpha <= 0) || ($beta <= 0)) {
            return ExcelError::NAN();
        }

        if ($cumulative) {
            return 1 - \exp(0 - ($value / $beta) ** $alpha);
        }

        return ($alpha / $beta ** $alpha) * $value ** ($alpha - 1) * \exp(0 - ($value / $beta) ** $alpha);
    }
}