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Normally-Distributed Random Numbers

Found at comp.lang.php on 2002/11/22 and implemented in php:

exercise: rewrite in RubyLanguage

$done = false;
while (!$done)
{
    $u1 = rand() / getrandmax();
    $u2 = rand() / getrandmax();

    // Set V1 = 2U1 - 1, V2 = 2U2 -1, S = V1^2 + V2^2

    $v1 = 2*$u1 -1;
    $v2 = 2*$u2 -1;
    $s = $v1 * $v1 + $v2 * $v2;

    // If S > 1, return to step 1
    if ($s <= 1)
        $done = true;
}

// Now return the independent unit normals
$x = sqrt(-2 * log($s) / $s) * $v1;
$y = sqrt(-2 * log($s) / $s) * $v2;