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<?php
namespace PhpOffice\PhpSpreadsheet\Calculation\Engineering;
use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
use PhpOffice\PhpSpreadsheet\Calculation\Functions;
use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
class ErfC
{
use ArrayEnabled;
/**
* ERFC.
*
* Returns the complementary ERF function integrated between x and infinity
*
* Note: In Excel 2007 or earlier, if you input a negative value for the lower bound argument,
* the function would return a #NUM! error. However, in Excel 2010, the function algorithm was
* improved, so that it can now calculate the function for both positive and negative x values.
* PhpSpreadsheet follows Excel 2010 behaviour, and accepts nagative arguments.
*
* Excel Function:
* ERFC(x)
*
* @param mixed $value The float lower bound for integrating ERFC
* Or can be an array of values
*
* @return array|float|string
* If an array of numbers is passed as an argument, then the returned result will also be an array
* with the same dimensions
*/
public static function ERFC($value)
{
if (is_array($value)) {
return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
}
if (is_numeric($value)) {
return self::erfcValue($value);
}
return ExcelError::VALUE();
}
private const ONE_SQRT_PI = 0.564189583547756287;
/**
* Method to calculate the erfc value.
*
* @param float|int|string $value
*
* @return float
*/
private static function erfcValue($value)
{
$value = (float) $value;
if (abs($value) < 2.2) {
return 1 - Erf::erfValue($value);
}
if ($value < 0) {
return 2 - self::erfcValue(-$value);
}
$a = $n = 1;
$b = $c = $value;
$d = ($value * $value) + 0.5;
$q2 = $b / $d;
do {
$t = $a * $n + $b * $value;
$a = $b;
$b = $t;
$t = $c * $n + $d * $value;
$c = $d;
$d = $t;
$n += 0.5;
$q1 = $q2;
$q2 = $b / $d;
} while ((abs($q1 - $q2) / $q2) > Functions::PRECISION);
return self::ONE_SQRT_PI * exp(-$value * $value) * $q2;
}
}
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