/** Returns the probability mass function @param float $x The test value @param float $lambda The rate of events @return float The probability */ static function getPmf($x, $lambda = 1) { return exp(-$lambda) * pow($lambda, $x) / \PHPStats\Stats::factorial($x); }
public function test_factorial() { $this->assertEquals(1, Stats::factorial(0)); $this->assertEquals(1, Stats::factorial(1)); $this->assertEquals(2, Stats::factorial(2)); $this->assertEquals(120, Stats::factorial(5)); $this->assertEquals(3628800, Stats::factorial(10)); }