My head hurts...

Cant you just move everyone over one spot at a time. Then when they are in pin 1 third player they go to pin 2 first player? Everyone will play in the same spots once. Is that what you meant? Or did you actually want someone to fill out all 13 rounds for you?

Edit: i just saw the part about everyplayer faceing each person twice.

If i could remember back to differetial equations in college there is probably a solution. Too bad i dropped out of that class

You can do it with matchplay if you do four player groups. Not sure if you can force matchplay to give you three player groups if it can give you four player groups.

Sorry, but this "problem" is worth more than $20 of time!!!

This might help:

http://www.printyourbrackets.com/roundrobin.html

A solution where each player plays against each other player exactly 2 times might not be possible. I can't neither prove or disprove this. I did find a solution so that each player plays against each other player at least 1 time but no more than 3 times. Shown below.

13 players are numbered 0 - 12.

round 1
2 8 9
3 11 12
1 4 10
5 6 7
round 2
4 9 11
6 8 10
2 3 7
0 5 12
round 3
1 7 11
3 6 8
4 5 9
0 10 12
round 4
0 4 6
5 8 10
7 11 12
1 2 9
round 5
0 1 5
2 6 11
7 10 12
3 8 9
round 6
1 10 11
0 3 9
4 8 12
2 6 7
round 7
4 8 11
7 9 10
2 5 12
0 1 3
round 8
1 5 8
3 6 10
0 9 11
2 4 12
round 9
0 4 7
1 9 12
5 6 11
2 3 10
round 10
2 4 10
3 5 11
1 6 12
0 7 8
round 11
3 4 5
6 7 9
0 1 2
8 11 12
round 12
7 10 12
1 5 9
3 6 8
0 2 4
round 13
2 6 11
1 4 10
7 8 9
0 3 5

crosstable showing how many times the players play against each other.

#0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12
#0. 0 3 2 3 3 3 1 2 1 2 1 1 2
#1. 0 0 2 1 2 3 1 1 1 3 3 2 2
#2. 0 0 0 2 3 1 3 2 1 2 2 2 2
#3. 0 0 0 0 1 3 3 1 3 2 2 2 1
#4. 0 0 0 0 0 2 1 1 2 2 3 2 2
#5. 0 0 0 0 0 0 2 1 2 2 1 2 2
#6. 0 0 0 0 0 0 0 3 3 1 2 3 1
#7. 0 0 0 0 0 0 0 0 2 3 3 2 3
#8. 0 0 0 0 0 0 0 0 0 3 2 2 2
#9. 0 0 0 0 0 0 0 0 0 0 1 2 1
#10. 0 0 0 0 0 0 0 0 0 0 0 1 3
#11. 0 0 0 0 0 0 0 0 0 0 0 0 3
#12. 0 0 0 0 0 0 0 0 0 0 0 0 0

Looks good to me

I think the answer is 42.

This site is turning into a boho fiverr

I made some improvements to the algorithm, see if i can find a better solution.

Here's one with only 2 pairs that are out of line. Chances are that's as good as it gets.
Round 1
3 10 12
1 6 11
5 7 8
2 4 9
Round 2
0 4 12
6 8 9
2 7 10
3 5 11
Round 3
0 3 7
1 9 12
5 6 10
4 8 11
Round 4
1 8 10
0 9 11
4 6 7
2 5 12
Round 5
2 3 9
0 5 8
6 10 11
1 7 12
Round 6
2 8 11
0 6 7
1 3 4
9 10 12
Round 7
0 1 10
2 8 12
3 4 5
7 9 11
Round 8
2 4 6
3 8 10
1 5 9
0 11 12
Round 9
3 6 12
0 1 2
4 9 10
5 7 11
Round 10
0 3 8
5 6 12
1 4 7
2 10 11
Round 11
2 3 7
0 5 9
1 6 8
4 11 12
Round 12
1 2 5
7 8 12
3 6 9
0 4 10
Round 13
1 3 11
4 5 10
0 2 6
7 8 9

0 1 2 3 4 5 6 7 8 9 10 11 12
#0. 0 2 2 2 2 2 2 2 2 2 2 2 2
#1. 0 0 2 2 2 2 2 2 2 2 2 2 2
#2. 0 0 0 2 2 2 2 2 2 2 2 2 2
#3. 0 0 0 0 2 2 2 2 2 2 2 2 2
#4. 0 0 0 0 0 2 2 2 1 2 3 2 2
#5. 0 0 0 0 0 0 2 2 2 2 2 2 2
#6. 0 0 0 0 0 0 0 2 2 2 2 2 2
#7. 0 0 0 0 0 0 0 0 3 2 1 2 2
#8. 0 0 0 0 0 0 0 0 0 2 2 2 2
#9. 0 0 0 0 0 0 0 0 0 0 2 2 2
#10. 0 0 0 0 0 0 0 0 0 0 0 2 2
#11. 0 0 0 0 0 0 0 0 0 0 0 0 2
#12. 0 0 0 0 0 0 0 0 0 0 0 0 0

Nice job - did you write a program to do it for you?

Yeah, slow day at work I still wonder if there is a perfect solution to this. I leave it running over the weekend, maybe I luck into something.

Oh my head. Just use Brackelope and call it a day.

There you go kids, maths at work. Stay in school!

Nice work, Yoski!

Will this also satisfy:

Is this the only solution found, and was it done by brute force, with you running it all weekend?

Great work either way

I found several (= 4) solutions (see listing below) to the problem of each player facing each other player exactly 2 times. Those solutions are rather challenging to find. If you throw in the additional constraint that each player has to play each machine exactly 3 times I am not sure if a solution still exists. Maybe, maybe not.
I used:
- a good random number generator
- a permutation generator I wrote
- the algorithm kept track how many times each player played against each other player in a cross table shown above. At the beginning of each new round it created a list of player pairs with the fewest matches against each other. From that list it tried to randomly select up to 4 match ups (or as many as possible) without a player getting a double assignment. Then the 3rd player was randomly selected from the remaining players. If the result produced a pair with 3 match ups it reset and tried again with a new random permutation. It tried multiple attempts at each round before it gives up and starts over from round one. It typically runs about 24 hours before it finds a solution, sometimes more, sometimes less, there's a certain luck factor. I wrote it in Perl. If you want to play around with it some more I can send you the code. It's ugly and poorly commented. OK, back to work, I got bigger fish to fry

Solutions:
#1 solution
4 8 11
5 6 12
1 2 3
7 9 10
5 7 11
0 6 8
2 4 10
3 9 12
0 5 10
7 8 12
3 4 6
1 9 11
2 6 7
0 1 4
10 11 12
5 8 9
6 8 10
1 7 12
0 9 11
2 3 5
6 9 10
0 2 7
1 3 8
4 11 12
0 2 12
1 5 8
3 10 11
4 7 9
2 8 11
0 3 12
1 6 9
4 5 10
2 4 9
0 6 11
3 5 7
1 10 12
0 3 4
1 7 11
2 8 10
5 6 12
2 9 12
3 6 11
0 7 8
1 4 5
1 2 6
4 8 12
3 7 10
0 5 9
2 5 11
4 6 7
0 1 10
3 8 9
#2 solution
4 6 12
5 7 11
2 3 9
1 8 10
7 8 9
3 5 6
2 4 10
0 11 12
9 10 12
1 6 11
0 5 8
3 4 7
0 6 10
4 8 11
2 7 12
1 5 9
5 10 11
1 3 12
2 6 8
0 7 9
0 1 2
3 8 12
4 7 10
6 9 11
0 3 10
1 4 9
2 7 11
5 8 12
3 8 11
1 2 5
0 4 9
6 10 12
0 4 5
1 6 7
9 11 12
2 3 10
7 8 10
1 4 12
2 5 6
0 3 11
0 1 8
2 4 11
3 6 9
5 7 12
4 6 8
5 9 10
1 3 7
0 2 12
1 10 11
3 4 5
2 8 9
0 6 7
#3 solution
1 6 8
2 7 12
3 9 11
4 5 10
0 10 11
4 7 9
2 3 6
5 8 12
4 11 12
8 9 10
1 3 5
0 6 7
6 10 12
2 5 9
0 1 4
7 8 11
0 3 9
2 8 12
5 6 11
1 7 10
1 2 11
0 8 10
3 4 7
6 9 12
0 9 12
1 2 10
5 7 11
3 4 8
3 10 12
0 2 11
1 8 9
4 5 6
0 5 7
2 4 9
1 11 12
3 6 10
0 1 6
3 7 12
2 5 8
4 10 11
1 7 9
2 4 6
3 8 11
0 5 12
0 2 3
6 7 8
1 4 12
5 9 10
1 3 5
6 9 11
2 7 10
0 4 8
#4 solution
4 5 10
3 9 11
2 6 8
1 7 12
3 6 10
0 2 11
4 8 12
5 7 9
9 10 12
1 3 4
0 5 6
7 8 11
0 8 9
5 11 12
1 2 10
4 6 7
0 3 8
2 5 12
7 10 11
1 6 9
2 3 4
1 8 10
0 7 9
6 11 12
4 9 12
3 5 10
0 1 11
2 7 8
0 10 12
1 4 11
2 6 9
3 5 8
3 7 12
0 4 6
1 2 5
9 10 11
2 7 10
3 6 12
4 8 11
0 1 5
2 4 9
5 6 11
1 8 12
0 3 7
1 3 9
4 5 7
6 8 10
0 2 12
0 4 10
2 3 11
1 6 7
5 8 9

Saving this thread to my favorites. Outstanding work by Yoski

Marcus

Put the code on github plz.

Yoski

care for another challenge?

we run a WI cross league event each year. There are 24 total players (8 from each respective league which represent a team)

We would like a format of 8 or 9 rounds of play; 3 player games. Each round a player from team 1 should play someone from team 2 and someone from team 3.

Ideally each player will play every other player with no (or as few as possible repeats) and also no (or as few as possible) game repeats.

I'll post the code. I hope to find some time to think about the 3 teams with 8 players problem. Right now I am busy, hopefully Friday or weekend.

I am pretty sure that no perfect solution exists. 3 teams with players 1,2,...,8 each.
So for example 111 would represent the match-up of all #1 players from the 3 teams. For none of those to ever meet again we can't have:
11* = ( 111, 112, 113, ..., 118)
1*1 = ( 111, 121, ..., 181)
*11 = (111, 211, 311, ..., 811)
So that's 3*8 = 24 minus the 2 duplicates of 111. This effectively eliminates 22 combinations just through a single match-up in the 1st round. Similarly for 222, 333, ..., 888 This makes for 8 first round matches times 22 eliminated combinations, for a total of 176 combinations gone after the 1st round. Similarly in the following rounds with some overlap of eliminated combinations between the rounds.
In total we only have 8*8*8 = 512 combinations. With roughly a third gone after round one we run out of combinations long before the problem is solved in round 8. In the end you will have some players that have met twice and others that haven't met at all.

thanks

that was my thought also.

i played around and got it so there were only a few repeats but was not able to get it all the way.

Was hoping a smart math person could plot out mathematcially the 'best' way with fewest repeats

Mathematically this is a mixed-integer programming problem and its complex because it's so overly constrained. Like Yoski mentioned the problem is with the players needing to play each other twice.

A short run (100 seconds) produces a poor solution with many players playing against each other 3-4 times. I'll run it over the weekend to see how good it can get.

here's the output and math model:
https://drive.google.com/open?id=0B_RoyxcAZ9L8WkxrNjBMeEF5ZUU
https://drive.google.com/open?id=0B_RoyxcAZ9L8cEl3TElteDVSU0k

Had fun playing with the model. Ignore my last post because the model was technically incorrect - it was allowing multiple people to sit out each round.

I'm just an amateur modeler, but I don't believe a solution exists given the constraints you described. There is an easy solution if you drop the player-vs-player requirement, and that solution is below.

Model: https://drive.google.com/open?id=0B_RoyxcAZ9L8cEl3TElteDVSU0k
Output: https://drive.google.com/open?id=0B_RoyxcAZ9L8WjBsRUJINFduSUU

snip (resized).PNG