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I made a couple significant changes to the code I posted here earlier.

One is a bug fix. The uasort on $players should be a usort. A uasort
leaves array keys intact, but my subsequent use of the array assumed that
array keys had been changed.

The other change is to the generation of the second two sets of ratings.
Between the second and third sets, I changed the order of the $players
array, essentially twisting it inside out in a spiral, so that the order
is very different. I then calculated the last two sets of ratings in the
otherwise same zig-zagging and reverse zig-zagging order of the first two
sets. Here's the code I used to change the order:

$neworder = array(); $midpoint = (int)floor($pc/2);
for ($i = 0; $i < $pc; $i++) {
	$neworder[$i] = ($i & 1) ? $players[$midpoint - (int)ceil($i/2)] :
$players[$midpoint + $i/2];
}
$players = $neworder;

I may change this in the future. I am thinking of evaluating all pairs in
a single order, based on which pairs have played the most games together.
This would start with the pairs that are most likely to give reliable
ratings and move on to pairs less likely to give reliable ratings. This
would help make the ratings of the latter more reliable when it finally
got to them, and it is probably the best order overall for reliable
ratings.