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RE: How to speed up this calculation?

• To: mathgroup at smc.vnet.net
• Subject: [mg37223] RE: How to speed up this calculation?
• From: "DrBob" <drbob at bigfoot.com>
• Date: Thu, 17 Oct 2002 00:08:54 -0400 (EDT)
• Reply-to: <drbob at bigfoot.com>
• Sender: owner-wri-mathgroup at wolfram.com

It's not clear what you mean by pairs that repeat themselves, but does
this do what you want?

pairs = Flatten[Outer[List, points, points, 1], 1];
Map[Union, Map[Sort, pairs, 2], 1]

DrBob

-----Original Message-----
From: Cheng Liu [mailto:cliu at lanl.gov] 
To: mathgroup at smc.vnet.net
Subject: [mg37223]  How to speed up this calculation?


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
and 
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 lanl.gov
====================================================