| public testRisingFactorialAsLahNumberAndFallingFactorial ( integer $x, $n ) | ||
| $x | integer | |
public function testRisingFactorialAsLahNumberAndFallingFactorial(int $x, $n)
{
$x⁽ⁿ⁾ = Combinatorics::risingFactorial($x, $n);
$∑L⟮n、k⟯x₍k₎ = 0;
for ($k = 1; $k <= $n; $k++) {
$x₍k₎ = Combinatorics::fallingFactorial($x, $k);
$L⟮n、k⟯ = Combinatorics::lahNumber($n, $k);
$∑L⟮n、k⟯x₍k₎ += $L⟮n、k⟯ * $x₍k₎;
}
$this->assertEquals($x⁽ⁿ⁾, $∑L⟮n、k⟯x₍k₎);
}