Weibull.php
1.7 KB
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<?php
namespace PhpOffice\PhpSpreadsheet\Calculation\Statistical\Distributions;
use PhpOffice\PhpSpreadsheet\Calculation\Exception;
use PhpOffice\PhpSpreadsheet\Calculation\Functions;
class Weibull
{
/**
* 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
* @param mixed $alpha Float alpha Parameter
* @param mixed $beta Float beta Parameter
* @param mixed $cumulative Boolean value indicating if we want the cdf (true) or the pdf (false)
*
* @return float|string (string if result is an error)
*/
public static function distribution($value, $alpha, $beta, $cumulative)
{
$value = Functions::flattenSingleValue($value);
$alpha = Functions::flattenSingleValue($alpha);
$beta = Functions::flattenSingleValue($beta);
$cumulative = Functions::flattenSingleValue($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 Functions::NAN();
}
if ($cumulative) {
return 1 - exp(0 - ($value / $beta) ** $alpha);
}
return ($alpha / $beta ** $alpha) * $value ** ($alpha - 1) * exp(0 - ($value / $beta) ** $alpha);
}
}