66 lines
2.4 KiB
PHP
66 lines
2.4 KiB
PHP
<?php
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namespace PhpOffice\PhpSpreadsheet\Calculation\Statistical\Distributions;
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use PhpOffice\PhpSpreadsheet\Calculation\ArrayEnabled;
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use PhpOffice\PhpSpreadsheet\Calculation\Exception;
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use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
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use PhpOffice\PhpSpreadsheet\Calculation\MathTrig;
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class Poisson
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{
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use ArrayEnabled;
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/**
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* POISSON.
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*
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* Returns the Poisson distribution. A common application of the Poisson distribution
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* is predicting the number of events over a specific time, such as the number of
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* cars arriving at a toll plaza in 1 minute.
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*
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* @param mixed $value Float value for which we want the probability
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* Or can be an array of values
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* @param mixed $mean Mean value as a float
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* Or can be an array of values
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* @param mixed $cumulative Boolean value indicating if we want the cdf (true) or the pdf (false)
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* Or can be an array of values
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*
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* @return array|float|string The result, or a string containing an error
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* 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 distribution(mixed $value, mixed $mean, mixed $cumulative): array|string|float
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{
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if (is_array($value) || is_array($mean) || is_array($cumulative)) {
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return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $mean, $cumulative);
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}
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try {
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$value = DistributionValidations::validateFloat($value);
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$mean = DistributionValidations::validateFloat($mean);
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$cumulative = DistributionValidations::validateBool($cumulative);
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} catch (Exception $e) {
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return $e->getMessage();
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}
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if (($value < 0) || ($mean < 0)) {
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return ExcelError::NAN();
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}
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if ($cumulative) {
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$summer = 0;
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$floor = floor($value);
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for ($i = 0; $i <= $floor; ++$i) {
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/** @var float $fact */
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$fact = MathTrig\Factorial::fact($i);
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$summer += $mean ** $i / $fact;
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}
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return exp(0 - $mean) * $summer;
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}
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/** @var float $fact */
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$fact = MathTrig\Factorial::fact($value);
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return (exp(0 - $mean) * $mean ** $value) / $fact;
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}
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}
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