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Re: Obtaining terms in an expansion

by DungeonKeeper (Novice)
on Jan 06, 2006 at 08:42 UTC ( #521428=note: print w/replies, xml ) Need Help??

in reply to Obtaining terms in an expansion

Math::Combinatorics can be used to iterate through the 2**N permutations subsets.

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Re^2: Obtaining terms in an expansion
by pKai (Priest) on Jan 06, 2006 at 12:52 UTC

    Actually 2**N is the number of subsets of a set of cardinality N, while the number of permutations of a set of N distinct elements is N! (facultyfactorial).

    ivancho used the subset theme quite succesfully in this node above.

      In a way you are correct, except that it's "factorial" not "faculty" - I used the word permutations a bit too loosely.

      However, the module Math::Combinatorics can still be used to iterate through the 2**N subsets as well as the nCr combinations and the N! permutations.

        Thank you, for pointing me to the "factorial"
        Note to self: Don't transfer mathematical/technical terms from German to English without consulting a dictionary first.

        Also, would you be able to give example code for the subset iteration with Math::Combinatorics?

        If there is an easy way to do so, it has escaped me.

        The closest I saw in the docs was that example to generate:
        "Morse signals: diferent signals of 3 positions using the two symbols - and .".

        Now Morse signals of length 3 are surely one-to-one and onto the subsets of a 3 element set (set elements = pos in signal; element not/contained = dot/dash)

        The given iteration using next_multiset and next_string is like computing 2**n as sumk=0..n nCk

        At least this is not trivial application of the modules methods.

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