Description:
------------
The existing hypot() function is limited to finding the hypotenuse of a right-angled triangle in two dimensions ($h = hypot($x,$y)), when in fact it is well-defined for higher dimensions as well as the length of the diagonal of a (hyper)cuboid with edge lengths $x,$y,$z...; it's the square root of the sum of the squares of the edge lengths.

For geometric purposes it would be helpful to have at least hypot($x,$y,$z). The existing alternatives are sqrt($x*$x+$y*$y+$z*$z) or hypot(hypot($x,$y),$z). The latter is (not surprisingly) markedly slower, and also less accurate.

Test script:
---------------
function length($v1, $v2)
{
    return hypot($v1[0]-$v2[0], $v1[1]-$v2[1], $v1[2]-$v2[2]);
}

$v1 = array(1, 1, 1);
$v2 = array(5, 6, 1);
echo length($v1, $v2);


Expected result:
----------------
6.4031242374328

Actual result:
--------------
A warning about hypot expecting exactly two parameters, and a NULL return value.