$twoSqrtPi
$twoSqrtPi
ERF(float $lower, float $upper = null) : float|string
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])
| float | $lower | lower bound for integrating ERF |
| float | $upper | upper bound for integrating ERF. If omitted, ERF integrates between zero and lower_limit |
<?php
namespace PhpOffice\PhpSpreadsheet\Calculation\Engineering;
use PhpOffice\PhpSpreadsheet\Calculation\Functions;
class Erf
{
private static $twoSqrtPi = 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 float $lower lower bound for integrating ERF
* @param float $upper upper bound for integrating ERF.
* If omitted, ERF integrates between zero and lower_limit
*
* @return float|string
*/
public static function ERF($lower, $upper = null)
{
$lower = Functions::flattenSingleValue($lower);
$upper = Functions::flattenSingleValue($upper);
if (is_numeric($lower)) {
if ($upper === null) {
return self::erfValue($lower);
}
if (is_numeric($upper)) {
return self::erfValue($upper) - self::erfValue($lower);
}
}
return Functions::VALUE();
}
/**
* ERFPRECISE.
*
* Returns the error function integrated between the lower and upper bound arguments.
*
* Excel Function:
* ERF.PRECISE(limit)
*
* @param float $limit bound for integrating ERF
*
* @return float|string
*/
public static function ERFPRECISE($limit)
{
$limit = Functions::flattenSingleValue($limit);
return self::ERF($limit);
}
//
// Private method to calculate the erf value
//
public static function erfValue($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 / $sum) > Functions::PRECISION);
return self::$twoSqrtPi * $sum;
}
}