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combinatoricspari-gp

Iterating over distinct permutations of a vector in Pari/GP

I want to iterate over all distinct permutations of a vector. I have tried doing this by using vecextract() in combination with numtoperm() to create a vector of permutations, and vecsort(,,,8) to remove equivalent permutations.

Unfortunately, this doesn't scale well: the maximum size of a vector within my current stack size of 4GB is less than 12!, and my machine only has 16GB.

Is there a way to do this without running out of memory, maybe by generating the k-th distinct permutation directly?

Solution

  • There is nothing built into PARI for this. I would suggest reading How to generate all the permutations of a multiset?.