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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

1137.0. "Max. 3 digit combination for X numbers." by DNEAST::FREEMAN_KEVI (The Squeeky Wheel = Neglect) Tue Oct 10 1989 09:58

    Can someone please help me with a formula or some other method of
    answering the following problem.  I need to find the maximum
    number of three digit combinations from any given amount of numbers.
    For example, I have 15 players and each player needs to play each other
    only once.  Players can play in two player matches but ideally I can
    reduce the number of matches by having as many three player matches
    along with the necessity to have two player matches ie. an even number
    of players.  I do know that a 9 player config. will result in 12 three
    player matches by using a matrix below and come up with 13 for 11
    players using roughly the same matrix.  If I choose numbers in a more
    random manner I get 15.
    
          12312      I circle diagonally, up/down, and across. to achieve 12
          45645
          78978
    
    Regards, Kevin
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1137.1WONDER::COYLEOnly 48.8% of my former self!Tue Oct 10 1989 17:4023
    I do not really understand what you are trying to do; but I will
    answer the question about finding the Number of Three Digit
    Combinationsfrom a given number of Numbers.
    
    Where the given number is  N:
    
      COMBINATIONS = N*(N-1)*(N-2)/6
    
         Basicaly you take the nuber of possible first choices, times
         the number of send choices, times the number of third choices.
    
         This give the number of three digit Permutations.  Since you
         want combinations, persumably because the order of choices
         wasn't important, you divide by the number of arrangements
         of the three selected numbers.  Which you get by having three
         first choices times two second choices with the final choice
         being already decided.
    
    If you can better explain what you are really truing to do I will
    try to help.
    
    -Joe
      
1137.2Let me know if you need more info!DNEAST::FREEMAN_KEVIThe Squeeky Wheel = NeglectWed Oct 11 1989 09:1421
    Joe,

    Sorry for not making myself clear.  I indicated that each player was to
    play against the other players ONLY once.  I failed to indicate that
    all players were to play against one another.  For example using 9 players.

    12312
    45645   I get 123, 456, 789, 147, 258, 369, 159, 267, 348, 357, 168, 249
    78978   by circling 3 digit combo's diag. up/down, and across.

    By using your equation I get 84.  Anyway, if I try my matrix with 11
    players I get the same combo's as above and one other and the rest (16)
    of two player matches. 1 vs 10, 2 vs 10 etc.  That results in 12 three
    player matches and 16 two player matches.  If I randomly select combo's
    I've achieved 15 three player matches for the same 11 players.  Is
    there a formula that will at least tell me the max. number of 3 digit
    combo's for any value, and Ideally a formula that yields the combo's
    ie first digit = X, second digit = X + 2, third digit = X + 4 or
    something.
    
    Regards, Kevin
1137.3220 PossibilityiesWONDER::COYLEOnly 48.8% of my former self!Wed Oct 11 1989 11:15129
    When I go through the formulae I get 220 possible 3 player matches.
    I have also listed them below.  I suggest that you pick your matches
    from the bottom group, then from the next group up (picking out
    those that have not previously played) and so forth until you reach
    the top.
    
    -Joe
    
    
    Here are all of the combinations with Player 12:

   (55 Combinations)

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

    12   6   5    12   5  4    12  4  3    12  3  2    12  2  1
    12   6   4    12   5  3    12  4  2    12  3  2   
    12   6   3    12   5  2    12  4  1 
    12   6   2    12   5  1
    12   6   1    

   Here are all of the combinations with Player 11 but without 12:

   (45 Combinations)

    11  10   9    11   9  8    11  8  7    11  7  6    11  6  5
    11  10   8    11   9  7    11  8  6    11  7  5    11  6  4
    11  10   7    11   9  6    11  8  5    11  7  4    11  6  3
    11  10   6    11   9  5    11  8  4    11  7  3    11  6  2
    11  10   5    11   9  4    11  8  3    11  7  2    11  6  1
    11  10   4    11   9  3    11  8  2    11  7  1    
    11  10   3    11   9  2    11  8  1    
    11  10   2    11   9  1    
    11  10   1   

    11   5   4    11   4  3    11  3  2    11  2   1
    11   5   3    11   4  2    11  3  2  
    11   5   2    11   4  1    

   Here are all of the combinations with Player 10 but without 11 and 12:

   (36 Combinations)

    10   9   8    10   8  7    10  7  6    10  6   5   10  5   4
    10   9   7    10   8  6    10  7  5    10  6   4   10  5   3
    10   9   6    10   8  5    10  7  4    10  6   3   10  5   2
    10   9   5    10   8  4    10  7  3    10  6   2   10  5   1
    10   9   4    10   8  3    10  7  2    10  6   1 
    10   9   3    10   8  2    10  7  1    
    10   9   2    10   8  1    
    10   9   1 

    10   4   3    10   3  2    10  2  1
    10   4   2    10   3  1 
    10   4   1

   Here are all of the combinations with Player 9 but without 10 through 12:

   (28 Combinations)

    9  8  7    9  7  6    9  6  5    9  5  4    9  4  3    9  3  2    9  2  1
    9  8  6    9  7  5    9  6  4    9  5  3    9  4  2    9  3  1
    9  8  5    9  7  4    9  6  3    9  5  2    9  4  1    
    9  8  4    9  7  3    9  6  2    9  5  1             
    9  8  3    9  7  2    9  6  1    
    9  8  2    9  7  1
    9  8  2

   Here are all of the combinations with Player 8 but without 9 through 12:

   (21 Combinations)

    8  7  6    8  6  5    8  5  4    8  4  3    8  3  2    9  2  1         
    8  7  5    8  6  4    8  5  3    8  4  2    8  3  1    
    8  7  4    8  6  3    8  5  2    8  4  1
    8  7  3    8  6  2    8  5  1
    8  7  2    8  6  1
    8  7  1

   Here are all of the combinations with Player 7 but without 8 through 12:

   (15 Combinations)

    7  6  5    7  5  4    7  4  3    7  3  2    7  2  1
    7  6  4    7  5  3    7  4  2    7  3  2   
    7  6  3    7  5  2    7  4  1    
    7  6  2    7  5  1   
    7  6  1

   Here are all of the combinations with Player 6 but without 7 through 12:

   (10 Combinations)

    6  5  4    6  4  3    6  3  2    6  2  1
    6  5  3    6  4  2    6  3  1
    6  5  2    6  4  1   
    6  5  1

   Here are all of the combinations with Player 5 but without 6 through 12:

   (6 Combinations)

    5  4  3    5  3  2    5  2  1
    5  4  2    5  3  1
    5  4  1    

   Here are all of the combinations with Player 4 but without 5 through 12:

   (3 Combinations)

    4  3  2    4  2  1
    4  3  1

   Here are all of the combinations with Player 3 but without 4 through 12:

   (1 Combination)

    3  2  1


1137.4ALIEN::POSTPISCHILAlways mount a scratch monkey.Wed Oct 11 1989 15:1320
    Re .1, .3:
    
    .0 isn't looking for all three-player combinations.  It's just all
    two-player combinations grouped into listings of three players -- each
    item of three players represents three two-player combinations.
    
    
    Re .2:
    
    When it is possible to represent all the matches with groups of three,
    there will be n(n-1)/6 such groups.  But that is only possible when n
    or n-1 is a multiple of three.  When n has a remainder of two when
    divided by three, it will not be possible to represent all the
    two-player combinations with groups of three, because there are
    n(n-1)/2 two-player combinations, and that won't be a multiple of three
    which can be made into groups of three players, each group representing
    three two-player combinations. 
    
    
    				-- edp 
1137.5may work for numbers greater that 9?DNEAST::FREEMAN_KEVIThe Squeeky Wheel = NeglectThu Oct 12 1989 12:248
    Eric,
    
    If I were to use the number 6 for instance (6*5)/6=5 and there are only
    two varing combinations.  ie 146,235 and the rest will have to be two
    player combinations.  It may prove true for values above 9 though I
    haven't hacked it.
    
    Kevin,