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Building a list of all words of length less than k in a given

  • To: mathgroup at smc.vnet.net
  • Subject: [mg108338] Building a list of all words of length less than k in a given
  • From: NIUNIU LAO <laoniuli at gmail.com>
  • Date: Sun, 14 Mar 2010 05:14:23 -0500 (EST)

Hello group,
Is there a standard way to :
1)specify an alphabet, here for example the two-letter alphabet {f1,f2}
2)generate all words (aka monic monoid polynomials, aka noncommutative
products) of length less than or equal to N with {f1,f2}
3)get results in a list.
In my case, I f1,f2 are functions and the product is function composition,
which I want to then evaluate at one, or several values x.
Consequently I cheated by adding Identity to my alphabet and building all
Tuples: my solution is:

indices = DeleteDuplicates[Tuples[{f1, f2, Identity}, k]]
Table[Apply[Composition, indices[[p]]][x], {p, Length[indices]}]

However I guess I am being blundering and suboptimal: if someone knows a
more standard, better way, thank you for letting me know!
Thank you.
Regards,
LN



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