/**
Returns the cumulative distribution function, the probability of getting the test value or something below it
@param float $x The test value
@param float $df The degrees of freedeom. Default 1
@return float The probability
*/
static function getCdf($x, $df = 1)
{
$return = 1 - 0.5 * \PHPStats\Stats::regularizedIncompleteBeta($df / 2, 0.5, $df / (pow($x, 2) + $df));
//Valid only for $x > 0
if ($x < 0) {
return 1 - $return;
} elseif ($x == 0) {
return 0.5;
} else {
return $return;
}
}
/**
Returns the cumulative distribution function, the probability of getting the test value or something below it
@param float $x The test value
@param float $alpha The minimum parameter. Default 0.0
@param float $beta The maximum parameter. Default 1.0
@return float The probability
*/
static function getCdf($x, $alpha = 1, $beta = 1)
{
return \PHPStats\Stats::regularizedIncompleteBeta($alpha, $beta, $x);
}
public function test_regularizedIncompleteBeta()
{
$this->assertEquals(0.25, round(Stats::regularizedIncompleteBeta(1, 1, 0.25), 5));
$this->assertEquals(0.4375, round(Stats::regularizedIncompleteBeta(1, 2, 0.25), 5));
$this->assertEquals(0.0625, round(Stats::regularizedIncompleteBeta(2, 1, 0.25), 5));
$this->assertEquals(0.73343, round(Stats::regularizedIncompleteBeta(5, 5, 0.6), 5));
$this->assertEquals(0.94269, round(Stats::regularizedIncompleteBeta(5, 8, 0.6), 5));
}