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Re: Eliminating intermediate results

  • To: mathgroup at smc.vnet.net
  • Subject: [mg91578] Re: Eliminating intermediate results
  • From: Ray Koopman <koopman at sfu.ca>
  • Date: Thu, 28 Aug 2008 03:16:35 -0400 (EDT)
  • References: <200808250905.FAA24382@smc.vnet.net> <g90bfc$n8o$1@smc.vnet.net>

On Aug 27, 3:41 am, Mariano Su=E1rez-Alvarez
<mariano.suarezalva... at gmail.com> wrote:
> [...]
> Notice my example was just an example. The context
> it came from needed not the length of the list but the
> combinations themselves.

P can also be used to get the compositions themselves,
without using excess intermediate storage:

Timing@Length[a = Select[Compositions[30,6],FreeQ[#,0]&]]
Timing@Length[b = Flatten[Permutations[#+1]&/@P[30-6,6],1]]
a === Sort[b]

{23.97 Second,118755}
{0.11 Second,118755}
True


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