/**
* Returns the probability mass function
*
* @param float $x The test value
* @param float $p The probability of success per trial
* @param int $n The number of trials
* @return float The probability
*/
public static function getPmf($x, $p = 0.5, $n = 1)
{
return \PHPStats\Stats::combinations($n, $x) * pow($p, $x) * pow(1 - $p, $n - $x);
}
/**
Returns the cumulative distribution function, the probability of getting the test value or something below it
@param float $x The test value
@param int $L The population size
@param int $m The number of interesting elements in the population
@param int $n The number of draws from the population
@return float The probability
*/
static function getCdf($x, $L = 1, $m = 1, $n = 1)
{
$x = floor($x);
$L = floor($L);
$m = floor($m);
$n = floor($n);
if ($L >= 1 && $m >= 0 && $n >= 0) {
$sum = 0;
for ($i = 0; $i <= $x; $i++) {
$sum += \PHPStats\Stats::combinations($m, $i) * \PHPStats\Stats::combinations($L - $m, $n - $i) / \PHPStats\Stats::combinations($L, $n);
}
return $sum;
} else {
return 0.0;
}
}
public function test_combinations()
{
$this->assertEquals(1, Stats::combinations(1, 1));
$this->assertEquals(2, Stats::combinations(2, 1));
$this->assertEquals(6, Stats::combinations(4, 2));
$this->assertEquals(1, Stats::combinations(5, 5));
$this->assertEquals(56, Stats::combinations(8, 5));
}