Komi

    Keywords: Rules, Go term

Chinese: 貼目 (tiē mù)
Japanese: (komi)
Korean: 덤(dum)

Komi is a Japanese go term adopted into English. In a game of Go, Black has the advantage of first move. In order to compensate for this, White can be given an agreed, set number of points before starting the game. These points are called komi. The English term "compensation points" or simply "compensation" is often used as a translation for komi, which is short for komidashi.[5]

A typical value for komi is in the region of 6 points, but numerous different values have been used in practice - see below for details. To prevent a drawn game in the case of jigo, the komi is commonly set to a fractional value such as 5.5 (which is a succinct way of expressing "White gets 5 points compensation and wins in the case of jigo").

With the notable exception of the Oteai, almost all tournaments nowadays, both amateur and professional, use komi. But this has not always been so. In fact, komi was rarely used in professional tournaments before 1937, and its gradual introduction into professional play was not without controversy.

The usual komi in Japan was for some time 4.5 points (specified as 4 points with White winning jigo)[4], although even lower values were commonly used early on. In 1955 the Oza became the first tournament to adopt 5.5. Today the standard komi in Japan is 5.5 points, although the Nihon Ki-in decided to change to 6.5 in September 2002.[1] Korea also used to use 5.5, but is already in the process of switching to 6.5.[2]. The usual komi in China was formerly 5.5, but 7.5 is now standard.[3] The Ing rules also have a komi of 7.5, specified as 8 points with Black winning jigo. Western countries often used to follow Japanese practice in using a komi of 5.5 points, but tournaments with komi set at 6 or 6.5 are not uncommon. The New Zealand rules specify a komi of 7. The American Go Association changed komi from 5.5 to 7.5 in August 2004, effective 2005. John Fairbairn has written on the History of Komi.

Because of the difficulty of determining a fair komi, a few amateur tournaments have adopted a system whereby players arrive at the komi through some form of bidding (Auction Komi).

The Correct Komi

In theory, the correct komi for a given ruleset is a well-defined concept: it is the number of points by which Black would win given perfect play by both sides. Unless the ruleset allows fractional winning margins (which none of the common ones do), this is necessarily a whole number. Due to the absence of perfect players this number cannot be determined with certainty, but it is possible to make a reasonable guess at it, at least for some rulesets.

Josh?: Going out on a limb, I suggest that the idea of "perfect play" is a poor way to set komi. Defining perfect play, even a perfect move, is not an easy thing to do, even for a professional. Furthermore, what relevance does perfect play have to "actual play". Even professionals make mistakes. So how useful is this idea for the rest of us?!

I suggestion abandoning the impractical notion of perfect play when setting komi and replacing it with a komi that is determine by the play of two equal opponents. I anticipate at least two objections to this idea: (1) How can you get two perfectly equal players? doesn't this suffer the same problem as requiring perfect play? (2) The play of two equal players could be awful - would you want the komi to be established by awful play?

Firstly, go programs provide can be used to get two perfectly equal players, e.g. get GnuGo to play against GnuGo. Have the programs play one another a large number of times with a given komi and the calculate the ratio of white wins to black wins (I am adopting an idea that as proposed elsewhere on SL, to use the win/loss ratio as a measure of the effect of the komi rather than the actual score. This means that there is no problem with resignation.)

Secondly, when two players of equal rank play they use some value of the komi (depending on the rule set used), but this komi does not change if the players are 9 kyu or 9 dan. So if the komi is correct for both 9 kyu and 9 dan that suggests that the komi is appropriate for perfect play, awful play, and everything in between! If that is the case, why is it problematic to base the komi upon the awful play of two evenly match players -- we assume it anyway! This brings me to what I consider the big question mark in my proposal: That the komi is independent of the players rank, it is only the difference in the ranks that is important. Is this actually true? I don't know if it is but, again, I think that computer go programs can assist. There are several versions of computer programs that play go and they play at different strengths. Above I describe a procedure for estimating the komi using one go program. Find the "fair komi" for each program. Does the "fair komi" differ between programs? I expect that there will be differences but I am curious to see what the difference would be like. If the difference is small, then the case for having a "one-size-fits-all" komi seems good and therefore it also seems that using a go program, weak though it may be, could provide a better approach to determining the "fair komi".

I realize that I could be stirring up a hornets nest, but I am interest in what ojections people have to this idea or what improvements they could foresee. Also, if anyone knows of any data relevant to this approach, that would be interesting to see here as well :-)

When area scoring is used (as in Chinese, Ing, AGA and New Zealand rules), the winning margin without komi is always odd, unless there are an odd number of points in seki. Since seki is fairly rare, and since a komi of 5.5 points has proven insufficient in professional play, and since a komi of 9 is generally considered far too much, it seems likely that the correct komi is 7.

When territory scoring is used (as in Japanese and Korean rules), the score is usually either the same as with area scoring, or one point better for White. This suggests that the correct komi under territory scoring rules is either 6 or 7. (Statistical evidence from professional games suggests 7.)

This is faulty reasoning. There needs to be made a distinction here between perfect komi as defined three paragraphs above and fair komi, which can be defined as that komi that gives a person against an evenly matched opponent a winning percentage that is as close to 50 percent as possible (treating a draw as half a win and half a loss). Perfect komi stays constant, but as insights change over time, fair komi can change with them, possibly even becoming fractional despite the used ruleset if the statistics can justify it.

The DragonGoServer offers a "proper komi feature" with fine-tuned komi intervals (..., 1.5, 2.0, 2.5, ...) to balance even minor rating differences to a 50:50 chance for both players.

BQM 67: How to adjust komi to board size?

See Handicap for smaller board sizes.

Statistics

illich: I did a little research using gobase.org.
I selected games on 19x19 with 5.5 komi. The results are:

Total: 12607 decided games
Black wins: 6701 games (53.15%)
White wins: 5906 games (46.84%)

And:
Black wins by 0.5: 369 games (2.92%)

So when you move games B+0.5 to W+0.5, it will be very close: 6332:6275. This means that komi of 6.5 is fair.

There is one brief analysis of komi and winning percentages at [ext] http://homepage.ntlworld.com/daniel.gilder/komistats.html and another at [DougsGoBlog#toc2].

Komi Analysis Naturally Skewed

The problem with most statistical komi analyses is that pros play to win only. The player who is behind will try to introduce complexities, while his opponent may be willing to play suboptimally in order to reduce complexities, so long as he gives up fewer points than his lead. This means completed games tend to gravitate toward small margins.

For this reason, the only reliable statistic is whether more games are won by W (or B) for a given komi. To get solid evidence of the perfect komi, we need good statistics for an upper bound. I have heard that more pro games are won by B in ING rules which use (effectively) 7.5 . This suggests the perfect komi in chinese scoring is at least 9. Since this is a scary amount of points to give W for the privilege of moving first, I would like to see much better statistics.

Searching GoBase at komi 8 gives 172 for B, 138 for W. Searching at komi 7.5 gives 483 for B, 566 for W. I did not filter for tournament games only, so this may include games where the stronger player is W.

Komi in Handicap Games

In handicap games a komi of half a point is often given to White in order to avoid a drawn game.

Komi can also be used in handicap games to compensate for differences in strength that exceed the traditional maximum handicap of 9 stones. Such a komi, given to Black rather than to White, is called "reverse komi" (gyaku komi in Japanese).

Komi can also be used to 'fine tune' a handicap. This is especially useful on small board Go, such as on a 9x9 board, where a single handicap stone compensates for a much greater difference in strength than it is the case on a 19x19 board.

Relation with the value of first move

Consider a game where black passes as first move. So white plays first move, and the game starts just as if white were black, unless that white has the komi advantage. This can be interpreted as if white played a game with reversed komi : the advantage he has is 2*komi (the komi he has + the komi that black has not)

We can assume that by passing, black lost an amount of points equal to the value of a standard move in the beginning, i.e 14 to 15 points according to professionnals.

To me, it is then normal that the value of komi be equal to half the value of a move in the opening...

Continuing the theory : I'm 6k, so I think the average value of my moves is about 1 point behind the professional's ones (15 stones is about 200 points, and a game is about 200 moves long). Well then I guess the komi that professionnals set is half a point too much for me ! Well I don't know about you, but in that case, I prefer playing white, with a decisive advantage of half a point !

Velobici: IMHO its not that amateurs play moves that are 1 point (or N points) less efficient than professionals. Consequently, over 200 moves end up 200 points amateurs are 200 points behind. Rather, amateurs play some moves that are professional level and some that are just horrible. The just horrible moves (errors) are the ones that mark us as amateurs. By reducing the magnitude of our errors, we improve...still we make moves that are somewhat less horrible in the midst of moves that are professional level. Once we stop making horrible moves, all our moves are professional level and we play like Jie Li.


[1] Nihon Ki-in looked at about 15,000 tournament games from 1996 to 2001 and found that Black won 51.86 % of all games, a margin of nearly 4 percent over White. The directors voted to change to 6.5 komi and negotiate with the Kansai Ki-in and tournament sponsors.

[2] The first significant professional tournament to adopt 6.5 komi seems to have been the 3rd LG Cup in 1998. This was an international tournament, but Korean-sponsored. Some Korean tournaments are still using 5.5 komi in 2002.

[3] Under Chinese rules there is very little practical difference between 5.5 and 6.5 komi, hence the jump directly to 7.5. Note also that in China it's usual to talk of 2.75 or 3.75 zi (子, meaning stone), rather than 5.5 or 7.5 komi.

[4] I was in Japan during the transition to 5.5 point komi. Then most pro games used a 4.5 point komi, but some used a 5 point komi with White winning jigo. I am unaware of any Japanese pro games with a 4 point komi with White winning jigo. -- Bill

[5]

Bill: Really? I thought that komidashi meant komi given, or giving komi.


See also:

For an alternative to komi, see Pie Rule.


This is a copy of the living page "Komi" at Sensei's Library.
(OC) 2005 the Authors, published under the OpenContent License V1.0.
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