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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 Erf
{
use ArrayEnabled;
private const TWO_SQRT_PI = 1.128379167095512574;
/**
* ERF.
*
* Returns the error function integrated between the lower and upper bound arguments.
*
* Note: In Excel 2007 or earlier, if you input a negative value for the upper or lower bound arguments,
* 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 ranges.
* PhpSpreadsheet follows Excel 2010 behaviour, and accepts negative arguments.
*
* Excel Function:
* ERF(lower[,upper])
*
* @param mixed $lower Lower bound float for integrating ERF
* Or can be an array of values
* @param mixed $upper Upper bound float for integrating ERF.
* If omitted, ERF integrates between zero and lower_limit
* Or can be an array of values
*
* @return array|float|string
* If an array of numbers is passed as an argument, then the returned result will also be an array
* with the same dimensions
*/
public static function ERF($lower, $upper = null)
{
if (is_array($lower) || is_array($upper)) {
return self::evaluateArrayArguments([self::class, __FUNCTION__], $lower, $upper);
}
if (is_numeric($lower)) {
if ($upper === null) {
return self::erfValue($lower);
}
if (is_numeric($upper)) {
return self::erfValue($upper) - self::erfValue($lower);
}
}
return ExcelError::VALUE();
}
/**
* ERFPRECISE.
*
* Returns the error function integrated between the lower and upper bound arguments.
*
* Excel Function:
* ERF.PRECISE(limit)
*
* @param mixed $limit Float bound for integrating ERF, other bound is zero
* Or can be an array of values
*
* @return array|float|string
* If an array of numbers is passed as an argument, then the returned result will also be an array
* with the same dimensions
*/
public static function ERFPRECISE($limit)
{
if (is_array($limit)) {
return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $limit);
}
return self::ERF($limit);
}
/**
* Method to calculate the erf value.
*
* @param float|int|string $value
*
* @return float
*/
public static function erfValue($value)
{
$value = (float) $value;
if (abs($value) > 2.2) {
return 1 - ErfC::ERFC($value);
}
$sum = $term = $value;
$xsqr = ($value * $value);
$j = 1;
do {
$term *= $xsqr / $j;
$sum -= $term / (2 * $j + 1);
++$j;
$term *= $xsqr / $j;
$sum += $term / (2 * $j + 1);
++$j;
if ($sum == 0.0) {
break;
}
} while (abs($term / $sum) > Functions::PRECISION);
return self::TWO_SQRT_PI * $sum;
}
}
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