You are doing the pairings...

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IM Jack Rudd
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You are doing the pairings...

Post by IM Jack Rudd » Mon Apr 23, 2012 10:21 pm

...and this scenario arises in the last round of a 5-round tournament. You are floating medians in both directions.

Downfloater from the 3½ scoregroup: Player #5, BWBW
In the 3 scoregroup are:
#2, WBWB
#10, WBWB
#12, bye BWW
#15, BWBW
#19, BWBW

2 has already played 15; no other relevant results-between-the-players

Which of these pairings do you go with?
(A) 5 v 12, 2 v 19, 10 v 15
(B) 10 v 5, 2 v 19, 15 v 12

Matthew Turner
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Re: You are doing the pairings...

Post by Matthew Turner » Mon Apr 23, 2012 10:30 pm

I think A is correct because it maintains the principle of top half against bottom half. I know this doesn't alway happen but as a rule of thumb for 'amateur' arbiters it is a good thing to aim for.

Alex McFarlane
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Re: You are doing the pairings...

Post by Alex McFarlane » Mon Apr 23, 2012 10:34 pm

With pairing A, I assume that having changed the colour of your downfloat you checked to see that it was still the correct person to bring down!

I see that your arguement for (a) is to pair the two medians, however everything else being equal I would tend to assume colour changes would be in the bottom half and would therefore go for (B). In adopting method (B) had your upfloat been a 'bottom half' player then I would have gone for (A) to avoid a median flip.

I trust this answer is totally incomprehensible to 90% of readers :lol:

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IM Jack Rudd
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Re: You are doing the pairings...

Post by IM Jack Rudd » Mon Apr 23, 2012 11:03 pm

Alex McFarlane wrote:With pairing A, I assume that having changed the colour of your downfloat you checked to see that it was still the correct person to bring down!
A good point, and it did affect the pairings in another section, but yes, 5 was the correct downfloater whichever colour the downfloater would have.

Alex Holowczak
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Re: You are doing the pairings...

Post by Alex Holowczak » Mon Apr 23, 2012 11:17 pm

Jack set me this poser via Facebook while on my way back from a league game. I did the pairings without seeing (A) and (B), and I ended up at (A).

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IM Jack Rudd
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Re: You are doing the pairings...

Post by IM Jack Rudd » Mon Apr 23, 2012 11:33 pm

The reason I set this question is that the pairings were queried at the time. Not by any of the six people in the question, but by #3, who was in the 3½ scoregroup and thought that pairing (A) - which was the one I went with - gave #5 an unfair advantage.

I won't mention who player #3 was, but I suspect most readers of this forum will already have guessed.

Roger de Coverly
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Re: You are doing the pairings...

Post by Roger de Coverly » Tue Apr 24, 2012 12:27 am

IM Jack Rudd wrote: I won't mention who player #3 was, but I suspect most readers of this forum will already have guessed.
I think the #5 had an advantage, but then so did the #3 seed in an earlier round, since colours were wrong for him to play the #1 seed and the #2 seed got the short straw.

Th #5 seed is well known to the forum as well and this result would only enhance his reputation.

I would have a marginal unease about a result which had a sole winner on 5/5 but the second place score being shared with 4.5 from 5. But accelerated pairings introduce their own problems.

Sean Hewitt
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Re: You are doing the pairings...

Post by Sean Hewitt » Tue Apr 24, 2012 7:51 am

IM Jack Rudd wrote:The reason I set this question is that the pairings were queried at the time. Not by any of the six people in the question, but by #3, who was in the 3½ scoregroup and thought that pairing (A) - which was the one I went with - gave #5 an unfair advantage.
An example of why the British idea of floating medians is a bad one in my opinion.

Alex McFarlane
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Re: You are doing the pairings...

Post by Alex McFarlane » Tue Apr 24, 2012 8:14 am

In a 5 round event the British system is median down highest graded up.
I was puzzled why it was median v median in Jack's example.

The 'Scottish' system of median down, highest up is perfectly logical. If you assume the upfloat to be the lowest rated in the scoregroup then that would be the pairing you would get under top half v bottom half.
Median down also avoids the lowest gradedgetting the bye and then stronger opponents than he should in subsequent rounds.

For long tournaments median up/median down can prevent the sole leader from getting a much tougher draw than would be desirable when compared to those of rivals in the score group below.

Sean Hewitt
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Re: You are doing the pairings...

Post by Sean Hewitt » Tue Apr 24, 2012 8:32 am

Personally, I prefer the FIDE rules of bottom down, top up. I think they normally make more sense (such as in this example) but, more importantly (to me), it is the correct way to pair according to the world governing body.

I accept that's a matter of choice but, if officials in Britain think that their way is superior, why don't they seek to change the official FIDE rules rather than 'go it alone' with different pairing rules?

Malcolm Clarke
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Re: You are doing the pairings...

Post by Malcolm Clarke » Tue Apr 24, 2012 7:31 pm

I often do the pairings for one of the Megafinals in the UK Chess Challenge and I must admit I try and find practical solutions without being too technical.

I have been in the past had only 6 or 7 players in a section with little grading information. In order for 6 players to complete a 6 player tournament in 5 rounds I start off pairing players with similar scores, but after the first 3 rounds I have to be careful that I am not left with 2 groups of 3 players who have yet to play each other.

With 7 players I usually look at the possible solutions with a couple of rounds left, but usually find 2 solutions of which I find it difficult to judge which is the most effective of these.

With comparatively small sections to work with my priorities not necessarily in order are 1) To keep within the schedule 2) To ensure different players receive byes where they are required 3) To ensure that players have their fair share of games with the white and black pieces 4) For players to play different opponents in each round. 5) To pair according to the results in the early rounds, and the later rounds if possible, whilst making sure I have a practical solution for all rounds.

If I achieve more than 1) to 5) it is a bonus and things like downfloats and medians are not things I attach high importance to, in the context I am operating.

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IM Jack Rudd
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Re: You are doing the pairings...

Post by IM Jack Rudd » Tue Apr 24, 2012 7:34 pm

Malcolm Clarke wrote: I have been in the past had only 6 or 7 players in a section with little grading information. In order for 6 players to complete a 6 player tournament in 5 rounds I start off pairing players with similar scores, but after the first 3 rounds I have to be careful that I am not left with 2 groups of 3 players who have yet to play each other.
The way to pair that is as follows:

Round 1: 1-6, 2-5, 3-4
Round 2: 1-2, 5-3, 6-4
Round 3: 3-1, 2-6, 4-5
Round 4: 1-4, 2-3, 6-5
Round 5: 5-1, 4-2, 3-6

Alex Holowczak
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Re: You are doing the pairings...

Post by Alex Holowczak » Tue Apr 24, 2012 8:23 pm

IM Jack Rudd wrote:
Malcolm Clarke wrote: I have been in the past had only 6 or 7 players in a section with little grading information. In order for 6 players to complete a 6 player tournament in 5 rounds I start off pairing players with similar scores, but after the first 3 rounds I have to be careful that I am not left with 2 groups of 3 players who have yet to play each other.
The way to pair that is as follows:

Round 1: 1-6, 2-5, 3-4
Round 2: 1-2, 5-3, 6-4
Round 3: 3-1, 2-6, 4-5
Round 4: 1-4, 2-3, 6-5
Round 5: 5-1, 4-2, 3-6
Yes, the best way to pair 6 players in 5 rounds is just by using the Berger tables for All-Play-Alls. No need to do it as a Swiss.

It's also probably the best way to pair 8 players in 6 rounds. You just choose, perhaps at random, which round you're missing out, and then make the necessary colour adjustments to end up with each player having 3 whites and 3 blacks.

I recently did this with a 10-player 7-round event at UKCC level. I dropped the last two rounds. Because it had a mix of ages, I decided to choose PINs such that the players in the same age group all met within the 7 rounds prescribed for the competition. I thought this was the fairest way of doing it.

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IM Jack Rudd
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Re: You are doing the pairings...

Post by IM Jack Rudd » Tue Apr 24, 2012 8:26 pm

Alex Holowczak wrote: Yes, the best way to pair 6 players in 5 rounds is just by using the Berger tables for All-Play-Alls. No need to do it as a Swiss.

It's also probably the best way to pair 8 players in 6 rounds. You just choose, perhaps at random, which round you're missing out, and then make the necessary colour adjustments to end up with each player having 3 whites and 3 blacks.
Round 1 would do the trick with no colour adjustments needed.

(Or you could do what I did at Keynsham a couple of years ago, where 8 players entered a 6-round Open section: I altered the time control in that section from G/25' to G/20' and fit seven rounds in the allotted time.)

Alex Holowczak
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Re: You are doing the pairings...

Post by Alex Holowczak » Tue Apr 24, 2012 8:32 pm

IM Jack Rudd wrote:(Or you could do what I did at Keynsham a couple of years ago, where 8 players entered a 6-round Open section: I altered the time control in that section from G/25' to G/20' and fit seven rounds in the allotted time.)
I didn't have this option, it being a UKCC. You needed x/6 to qualify, where from memory, x was 4. By extending the event to 7 rounds, this messed up the qualification threshold. In other circumstances, I agree that this is a reasonable solution.