       combinations problem

• To: mathgroup at smc.vnet.net
• Subject: [mg58563] combinations problem
• From: hrocht at mail15.com
• Date: Thu, 7 Jul 2005 05:35:54 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```hi
at first here is my program
<< DiscreteMath`Combinatorica`
lst1 = Table[i, {i, 100}]
Do[
lst2 = Table[Random[Integer, {1, 300}], {i, 100}];
lst3 = Transpose[{lst1, lst2}];
a = KSubsets[lst3, 2];
num = 0; Do[
If[
Abs(a[[i]][][] - a[[i]][][]) ==
Abs(a[[i]][][] - a[[i]][][]) || (a[[i]][]
[] +
a[[i]][][]) == (a[[i]][][] + a[[i]][]
[]),
num++;]
, {i, 1, 4950}];
If[num > 40, Print[num]; Print[lst2]];
, {j, 1, 2000}]

lst3 will have each element in lst2 together with its ordering
such as :
Take[lst3, {1, 3}]
{{1, 48}, {2, 295}, {3, 74}}
if we take all the possible combinations in lst3 taken in pairs as in
a = KSubsets[lst3, 2]
one sublist may be for a[]
{{1, 6}, {29, 34}}
the length of "a" will be 4950 which is number of possible
combinations for 100 elements taken in pairs.
the mission is to count the sublists such as
{{1, 6}, {29, 34}}  in which  abs[1-6]=abs[29-34]
or the sublists such as
{{1, 206}, {35, 172}}
in wich 1+206=35+172
and what is the biggest possible number for such sublists when we
supply our random or carefully designed lst2 ?
in the program above we want to display only the lst2 wich will give
num>40
how  could i make my program more speedy and more efficient?
thanks
Anton

```

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