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Re: How to speed up this calculation?

  • To: mathgroup at
  • Subject: [mg37212] Re: How to speed up this calculation?
  • From: "Steve Luttrell" <luttrell at>
  • Date: Thu, 17 Oct 2002 00:08:30 -0400 (EDT)
  • References: <aokc15$agm$>
  • Sender: owner-wri-mathgroup at

Oops! I didn't read the question properly. I hope I have got it right this

Union[Map[Sort, pairs]] does what you want.

Steve Luttrell
West Malvern, UK

"Cheng Liu" <cliu at> wrote in message
news:aokc15$agm$1 at
> Dear group,
>          I have the following question regarding a lengthy calculation
> using Mathematica:
> For given w points in x direction and h points in y direction, I can
> construct all the points using
>          h=10; w=8;
>          points=Flatten[Transpose[Outer[List,Range[w],Range[h]]],1]
> Next, I need to find all the possible pairs of point including points
> themselves, i.e., pair AA.  I can use
>          pairs=Outer[List,points,points,1]
> Then, I have to clear those pairs that repeat themselves, i.e., pair AB
> pair BA.  Also, when w and h are of the order of 1000s, the computation
> takes a very long time.  Is there a better way of doing the second part of
> the computation?  Thanks in advance.
> Sincerely
> Cheng
> ====================================================
> Cheng Liu, Ph.D.
> MST-8, Structure/Property Relations
> Materials Science and Technology Division
> Los Alamos National Laboratory
> Los Alamos, New Mexico 87545
> Phone: 505-665-6892 (office), 505-667-9950 (lab)
> Fax:   505-667-8021
> email: cliu at
> ====================================================

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