/**
* POISSON
*
* Returns the Poisson distribution. A common application of the Poisson distribution
* is predicting the number of events over a specific time, such as the number of
* cars arriving at a toll plaza in 1 minute.
*
* @param float $value
* @param float $mean Mean Value
* @param boolean $cumulative
* @return float
*
*/
public static function POISSON($value, $mean, $cumulative)
{
$value = Functions::flattenSingleValue($value);
$mean = Functions::flattenSingleValue($mean);
if (is_numeric($value) && is_numeric($mean)) {
if ($value < 0 || $mean <= 0) {
return Functions::NAN();
}
if (is_numeric($cumulative) || is_bool($cumulative)) {
if ($cumulative) {
$summer = 0;
for ($i = 0; $i <= floor($value); ++$i) {
$summer += pow($mean, $i) / MathTrig::FACT($i);
}
return exp(0 - $mean) * $summer;
} else {
return exp(0 - $mean) * pow($mean, $value) / MathTrig::FACT($value);
}
}
}
return Functions::VALUE();
}
/**
* BESSELJ
*
* Returns the Bessel function
*
* Excel Function:
* BESSELJ(x,ord)
*
* @access public
* @category Engineering Functions
* @param float $x The value at which to evaluate the function.
* If x is nonnumeric, BESSELJ returns the #VALUE! error value.
* @param integer $ord The order of the Bessel function. If n is not an integer, it is truncated.
* If $ord is nonnumeric, BESSELJ returns the #VALUE! error value.
* If $ord < 0, BESSELJ returns the #NUM! error value.
* @return float
*
*/
public static function BESSELJ($x, $ord)
{
$x = is_null($x) ? 0.0 : Functions::flattenSingleValue($x);
$ord = is_null($ord) ? 0.0 : Functions::flattenSingleValue($ord);
if (is_numeric($x) && is_numeric($ord)) {
$ord = floor($ord);
if ($ord < 0) {
return Functions::NAN();
}
$fResult = 0;
if (abs($x) <= 30) {
$fResult = $fTerm = pow($x / 2, $ord) / MathTrig::FACT($ord);
$ordK = 1;
$fSqrX = $x * $x / -4;
do {
$fTerm *= $fSqrX;
$fTerm /= $ordK * ($ordK + $ord);
$fResult += $fTerm;
} while (abs($fTerm) > 1.0E-12 && ++$ordK < 100);
} else {
$f_PI_DIV_2 = M_PI / 2;
$f_PI_DIV_4 = M_PI / 4;
$fXAbs = abs($x);
$fResult = sqrt(M_2DIVPI / $fXAbs) * cos($fXAbs - $ord * $f_PI_DIV_2 - $f_PI_DIV_4);
if ($ord & 1 && $x < 0) {
$fResult = -$fResult;
}
}
return is_nan($fResult) ? Functions::NAN() : $fResult;
}
return Functions::VALUE();
}
