LogNormal.php

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<?php

namespace PhpOffice\PhpSpreadsheet\Calculation\Statistical\Distributions;

use PhpOffice\PhpSpreadsheet\Calculation\Exception;
use PhpOffice\PhpSpreadsheet\Calculation\Functions;

class LogNormal
{
    public static function cumulative($value, $mean, $stdDev)
    {
        $value = Functions::flattenSingleValue($value);
        $mean = Functions::flattenSingleValue($mean);
        $stdDev = Functions::flattenSingleValue($stdDev);

        try {
            $value = DistributionValidations::validateFloat($value);
            $mean = DistributionValidations::validateFloat($mean);
            $stdDev = DistributionValidations::validateFloat($stdDev);
        } catch (Exception $e) {
            return $e->getMessage();
        }

        if (($value <= 0) || ($stdDev <= 0)) {
            return Functions::NAN();
        }

        return StandardNormal::cumulative((log($value) - $mean) / $stdDev);
    }

    public static function distribution($value, $mean, $stdDev, $cumulative = false)
    {
        $value = Functions::flattenSingleValue($value);
        $mean = Functions::flattenSingleValue($mean);
        $stdDev = Functions::flattenSingleValue($stdDev);
        $cumulative = Functions::flattenSingleValue($cumulative);

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

        if (($value <= 0) || ($stdDev <= 0)) {
            return Functions::NAN();
        }

        if ($cumulative === true) {
            return StandardNormal::distribution((log($value) - $mean) / $stdDev, true);
        }

        return (1 / (sqrt(2 * M_PI) * $stdDev * $value)) *
            exp(0 - ((log($value) - $mean) ** 2 / (2 * $stdDev ** 2)));
    }

    public static function inverse($probability, $mean, $stdDev)
    {
        $probability = Functions::flattenSingleValue($probability);
        $mean = Functions::flattenSingleValue($mean);
        $stdDev = Functions::flattenSingleValue($stdDev);

        try {
            $probability = DistributionValidations::validateProbability($probability);
            $mean = DistributionValidations::validateFloat($mean);
            $stdDev = DistributionValidations::validateFloat($stdDev);
        } catch (Exception $e) {
            return $e->getMessage();
        }

        if ($stdDev <= 0) {
            return Functions::NAN();
        }

        return exp($mean + $stdDev * StandardNormal::inverse($probability));
    }
}