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Last edit: 01:28, 4 October 2018

I've been always thinking about the pairing systems of meleerumble.

Once every combination of 10 bots had a run, the score is unbiased, which takes N = n! / (10! * (n - 10)!) ≈ 10^19 battles in current settings (n is the total of participants).

However we should get approximate score with feasible battles via monte carlo method. In current settings, ~10000 battles already gives a somewhat stable score (for the new participant).

Let each bot gets m battles, randomly selected from all (N / n) 10-bot combinations containing that bot, then the probability of meeting another specific bot in a battle is (N / n / (n - 1)) / (N / n) = 1 / (n - 1).

Assume that when a new bot is released, every battle contains that bot, then the probability of meeting that bot is 1 instead of 1 / (n - 1), which is highly biased.

To fix this, we have two options — mutate our current pairing systems to get unbiased score online, or to reset the entire meleerumble periodically.

Since the score of new bots are unbiased, all we need to do for an unbiased score is to ignore (n - 2) / (n - 1) biased battles randomly when calculating the score of an old bot. However this approach takes much more battles.

A more practical way is is, when bot A is added, for each battle, select another bot B randomly, and run melee battles containing those two bots as usual. A battle containing A, B and other 8 bots should yield 45 pairings, but only those matching (A, *) or (B, *) is taken into account. This produces 17 parings.

This scheme does not affect the pairings of the new bot itself at all, which is already unbiased; And for an old bot, the probability of being chosen as B is 1 / (n - 1), therefore the probability of a battle with A present being taken into account for old bots is 1 / (n - 1), the same as the unbiased one.

Xor (talk)10:29, 11 September 2018

Your second approach seems good, it will need patches on the client side so that if a priority pairing needs to happen it only uploads the battles which contain one of the priority bots. This filter will work fine for the 1v1 rumble as well.

Why don't we wait to update the client until this can be fixed too?

Skilgannon (talk)21:50, 11 September 2018

The only reason for upgrading earlier is that those two bugs are very annoying when running rumble client 7/24.

And it generally takes monthes for fnl to release a new version in normal cycle ;(

Anyway, since those two fixes are unrelated to robocode engine, one should expect no performance difference if we cherry pick the fix back to

Maybe we could release a special version of for those running rumble 7/24, before the melee pairing fix is released.

Or, we may just ask fnl whether he could please release soon after the meleerumble patch is applied.

Xor (talk)02:51, 12 September 2018

I patched robocode's roborumble by cherry-picking roborumble client fixes from and

The patched roborumble.jar can be downloaded from:

This should check participants list more often preventing retired bots from being battled and submitted nullifying smart battles. And on unstable network it won't upload 80000 duplicate battles for a single pairing any more. (See pulsar.PulsarNano 0.2.4 and ad.last.Bottom 1.0)

I suspect we should separate roborumble version and robocode version (since they are weakly dependent) and get roborumble bug fixes quicker than robocode, since roborumble bugs are generally more serious, and roborumble fixes has nothing to do with the rest of robocode users.

Currently fixes in roborumble takes almost a year to be actually deployed.

Xor (talk)05:57, 20 September 2018

I've enabled for uploads. Let's try it for a while and see how it goes. If we notice anything strange, well, the rumble probably needs a wipe some time soon anyway, and definitely melee.

Skilgannon (talk)17:18, 3 October 2018

I'll upgrade all my clients later and upload the same bot of mine with different version number to see the impact on score...

The melee part is already discussed, but why the 1v1 rumble needs a wipe as well? And how long it should take to reload the rumble? Or should we run the current rumble as a backup in parallel until the reload completes? (so that new players can still submit their bots)

Xor (talk)17:40, 3 October 2018
Edited by another user.
Last edit: 04:37, 18 October 2018

Seems something is wrong, ScalarN is suddenly first in mini, micro and nano rumble ! And ofcourse second in roborumble, which in itself is quite an accomplishment.

GrubbmGait (talk)01:07, 18 October 2018