/**
Returns the probability distribution function
@param float $x The test value
@param float $df The degrees of freedeom. Default 1
@return float The probability
*/
static function getPdf($x, $df = 1)
{
return pow(1 + pow($x, 2) / $df, -($df + 1) / 2) / (sqrt($df) * \PHPStats\Stats::beta(0.5, $df / 2));
}
/**
Returns the probability distribution function
@param float $x The test value
@param float $alpha The minimum parameter. Default 0.0
@param float $beta The maximum parameter. Default 1.0
@return float The probability
*/
static function getPdf($x, $alpha = 1, $beta = 1)
{
if ($x >= 0 && $x <= 1) {
return pow($x, $alpha - 1) * pow(1 - $x, $beta - 1) / \PHPStats\Stats::beta($alpha, $beta);
} else {
return 0.0;
}
}
public function test_beta()
{
$this->assertEquals(1, round(Stats::beta(1, 1), 2));
$this->assertEquals(0.5, round(Stats::beta(1, 2), 2));
$this->assertEquals(0.5, round(Stats::beta(2, 1), 2));
$this->assertEquals(0.0015873, round(Stats::beta(5, 5), 7));
$this->assertEquals(0.0002525, round(Stats::beta(5, 8), 7));
}
