Rating Script - Stuck :(

[Adrian Schneider]

I really hate php :(

Anyway, if someone can tell me why this won't work (everything works except the $probability) In cases where it should obviously spit out something like 50 (50% chance) it spits out 0.95834583.


<?php
////////////////////////////////////////////////////////
// MySQL & Form Setup //////////////////////////////////
////////////////////////////////////////////////////////
$connection = mysql_connect("localhost", "##CENSORED##", "##CENSORED##");
mysql_select_db("##CENSORED##_vbulletin");

$winner = $_POST['winner'];
$loser = $_POST['loser'];

$winnerq = mysql_query("SELECT `user`.`rating` FROM user WHERE username = '$winner' LIMIT 1");
$loserq = mysql_query("SELECT `user`.`rating` FROM user WHERE username = '$loser' LIMIT 1");
$winnerr = mysql_fetch_array($winnerq);
$loserr = mysql_fetch_array($loserq);


/////////////////////////////////////////////////////////
// Difference Determination /////////////////////////////
/////////////////////////////////////////////////////////
if ($winnerr[rating] > $loserr[rating])
{
$difference = $winnerr[rating] - $loserr[rating];
}
if ($winnerr[rating] < $loserr[rating])
{
$difference = $loserr[rating] - $winnerr[rating];
}
if ($winnerr[rating] == $loserr[rating])
{
$difference = 0;
}
////////////////////////////////////////////////////////
// Probability Determination ///////////////////////////
////////////////////////////////////////////////////////
$probability = 1/(1+10^($difference/400));



////////////////////////////////////////////////////////
// Winner K Determination //////////////////////////////
////////////////////////////////////////////////////////
if ($winnerr[rating] < 1300)
{
$wK = 50;
}
if ($winnerr[rating] > 1300 AND $winnerr[rating] < 1500)
{
$wK = 30;
}
if ($winnerr[rating] > 1500)
{
$wK = 20;
}


////////////////////////////////////////////////////////
// Loser K Determination ///////////////////////////////
////////////////////////////////////////////////////////
if ($loserr[rating] < 1300)
{
$lK = 50;
}
if ($loserr[rating] > 1300 AND $loserr[rating] < 1500)
{
$lK = 30;
}
if ($loserr[rating] > 1500)
{
$lK = 20;
}
/////////////////////////////////////////////////////////
// Modify by How Much ///////////////////////////////////
/////////////////////////////////////////////////////////
$winneradd = $wK * 1-$probability;
$losersub = $lK * $probability;
$winnernew = round($winnerr[rating] + $winneradd, 0);
$losernew = round($loserr[rating] - $losersub, 0);


/////////////////////////////////////////////////////////
// Update Rating ////////////////////////////////////////
/////////////////////////////////////////////////////////
$updatewinner = mysql_query("UPDATE user SET rating='$winnernew' WHERE username='$winner'");
$updateloser = mysql_query("UPDATE user SET rating='$losernew' WHERE username='$loser'");


/////////////////////////////////////////////////////////
// Test Variables (Diagnostics) /////////////////////////
/////////////////////////////////////////////////////////
echo
"$winner score has been changed from $winnerr[rating] to $winnernew <BR>
$loser score has been changed from $loserr[rating] to $losernew <BR>
Rating difference is $difference <BR>
The probability of winning was $probability";
?>

Edit: by the way the formula this is based off of (Blizzards) can be viewed here: http://www.starcraftdream.com/forums/league.php?do=scoring.

[Andreas]

Hmm, can you give example data for which the script does fail?
As I don't seem to understand what it's all about ...


if ($winnerr[rating] > $loserr[rating])
{
$difference = $winnerr[rating] - $loserr[rating];
}
if ($winnerr[rating] < $loserr[rating])
{
$difference = $loserr[rating] - $winnerr[rating];
}
if ($winnerr[rating] == $loserr[rating])
{
$difference = 0;
}


Why not just

$difference = abs($winnerr[rating] - $loserr[rating]);

[Adrian Schneider]

Just learning. :)

I didn't want a negative difference, so I made sure the one in front was larger. Not sure what the abs function does.

Say if the difference = 0, then obviously the probability of winning would be 50. Getting .095843573 or something similar, tells me something is wrong.

[Andreas]

Your formular is

$probability = 1/(1+10^($difference/400));


$difference is 0


$probability = 1/(1+10^0);


10^0 is 10


$probability = 1/(1+10);


And 1/11 is 0.09090... according to my calculator.
So what's wrong?

[Adrian Schneider]

Hmm I guess that is good news. Thanks

[Andreas]

I think your formula is wrong and your probably meant

$probability = 1/(1+pow(10, $difference/400));

as this will result in 0.5

[Adrian Schneider]

Fantastic, thanks a bunch. Fast response too. :)

[Andreas]

You're welcome :)

^ is an XOR operator, not powers - you have to use function pow() for that.

Function abs() does give the absolute value of the argument.