Elo rating

elo_rating.php

<?php

const K = 4;
const Z = 400;

$rating_a = 1200.0;
$rating_b = 1500.0;

$win = function ($r, $e) {
    return sprintf('%.2F', round($r + (K * (1 - $e)), 2));
};
$lose = function ($r, $e) {
    return sprintf('%.2F', round($r + (K * (0 - $e)), 2));
};
$draw = function ($r, $e) {
    return sprintf('%.2F', round($r + (K * (0.5 - $e)), 2));
};

$winning_per_average_a = 1 / (1 + (10 ** (($rating_b - $rating_a) / Z)));
$winning_per_average_b = 1 / (1 + (10 ** (($rating_a - $rating_b) / Z)));

echo "A:\n"
    . sprintf("    before-rating=%.5F\n", $rating_a)
    . sprintf("    win=%.5F\n", $win($rating_a, $winning_per_average_a))
    . sprintf("    lose=%.5F\n", $lose($rating_a, $winning_per_average_a))
    . sprintf("    draw=%.5F\n", $draw($rating_a, $winning_per_average_a))
    . "\n"
    . "B:\n"
    . sprintf("    before-rating=%.5F\n", $rating_b)
    . sprintf("    win=%.5F\n", $win($rating_b, $winning_per_average_b))
    . sprintf("    lose=%.5F\n", $lose($rating_b, $winning_per_average_b))
    . sprintf("    draw=%.5F\n", $draw($rating_b, $winning_per_average_b));