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