/**
* ZTEST
*
* Returns the Weibull distribution. Use this distribution in reliability
* analysis, such as calculating a device's mean time to failure.
*
* @param float $value
* @param float $alpha Alpha Parameter
* @param float $beta Beta Parameter
* @param boolean $cumulative
* @return float
*
*/
public static function ZTEST($dataSet, $m0, $sigma = null)
{
$dataSet = PHPExcel_Calculation_Functions::flattenArrayIndexed($dataSet);
$m0 = PHPExcel_Calculation_Functions::flattenSingleValue($m0);
$sigma = PHPExcel_Calculation_Functions::flattenSingleValue($sigma);
if (is_null($sigma)) {
$sigma = self::STDEV($dataSet);
}
$n = count($dataSet);
return 1 - self::NORMSDIST((self::AVERAGE($dataSet) - $m0) / ($sigma / SQRT($n)));
}