MaplePrimes - answers and comments on Question, randperm in MapleTA produces always the same permutation

Get a new seed for the pseudo-random number generator.

jaytreiman — Fri, 16 Nov 2012 23:05:58 Z

Maple always starts with the same seed for its pseudo-random number generator. What you need to do is to get new seed. For example, you could use, in MapleTA,

$seed=rand(1000,10000000);

to get a seed and then use

RandomTools[SetState](state=$seed);

within your maple code to get different permutations.

For example:

    \code{
      $n=3;
      $seed=rand(1000,10000000);
      $pa=maple("randomize();with(combinat);RandomTools[SetState](state=$seed);[randperm($n),randperm($n)]");

StringTools

Dave L — Tue, 20 Nov 2012 00:58:47 Z

I just found out the following piece of information. The combinat:-randperm command of Maple 16 makes an external call to a function in the {lib}mstring.{so,dll} shared library.

> showstat((combinat::Permutations)::Random);

(combinat::Permutations):-Random := proc()
   1   passign(procname,subsop(5 = "generate a random permutation",defun(convert(mstring_randperm,'string'),"mstring",(':-mtsafe') = true)));
   2   procname(args)
end proc

And it turns out the the seed for this is controlled by the StringTools:-Randomize command.

The following is done in the commandline interface of 64bit Maple 16.01 on Linux. The behavior seems similar in Maple 14.01 and 15.01.

> restart:          
> with(combinat):   
> L:=[1,2,3]:       
> randperm(L), randperm(L);

                             [2, 1, 3], [1, 3, 2]

> restart:                 
> with(combinat):          
> L:=[1,2,3]:              
> randperm(L), randperm(L);

                             [2, 1, 3], [1, 3, 2]

> restart:                 
> with(combinat):          
> StringTools:-Randomize():
> L:=[1,2,3]:
> randperm(L), randperm(L);

                             [1, 2, 3], [3, 2, 1]

> restart:                 
> with(combinat):          
> StringTools:-Randomize():
> L:=[1,2,3]:              
> randperm(L), randperm(L);

                             [3, 1, 2], [2, 1, 3]

Of course, this might be better handled in a centralized location (ie. the `randomize` command, and/or RandomTools package).

Dave Linder
Mathematical Software, Maplesoft

Thanks a lot. The proposed method seems to

MichaelKaplan — Sat, 17 Nov 2012 03:05:09 Z

Thanks a lot. The proposed method seems to work with RandomMatrix but didn't work for me with randperm. I now found a working but ineffective solution. I used

    \code{
      $m=4;      
      $s=range(4,100);
      $pb=maple("with(combinat,randperm):[seq(randperm($m),i=1..$s)]");

though I only need 2 permutations and use $pb[$s] and $pb[$s-1] in the rest of the program.

Oops, my mistake, wrong package.

jaytreiman — Sat, 17 Nov 2012 05:24:38 Z

The combinat package does not use the same seed. You can use the command

to get a permutation of the first n positive integers. This would mean using code similar to the following:

    \code{
      $n=3;      
      $seed=range(1000,10000000);
      $pb=maple("RandomTools[SetState](state=$seed);
             [Statistics:-Shuffle([seq(1..$n)]),Statistics:-Shuffle([seq(1..$n)])");

I hope that is better.