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MathGroup Archive 2006

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Re: Dynamic iterators in Do loop

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66418] Re: Dynamic iterators in Do loop
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Thu, 11 May 2006 05:36:16 -0400 (EDT)
  • Organization: The University of Western Australia
  • References: <e3js6u$8jt$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <e3js6u$8jt$1 at smc.vnet.net>, sai <iwillfail at gmail.com> 
wrote:

> I have an (n,n) matrix. I want to define an (m,m) matrix [m<n] whose elements 
> are defined from the (n,n) matrix. The value of n and m changes from problem 
> to problem. How can i do this in mathematica?

For an arbitrary matrix, say

  mat[n_] := Table[a[i, j], {i,n},{j,n}]

then the easiest way to extract a block of the matrix is to use Part 
with Range. For example,

  mat[10][[ Range[2,5],Range[3,6] ]]

extracts a 4 x 4 submatrix from the 10 x 10 matrix.

Cheers,
Paul

_______________________________________________________________________
Paul Abbott                                      Phone:  61 8 6488 2734
School of Physics, M013                            Fax: +61 8 6488 1014
The University of Western Australia         (CRICOS Provider No 00126G)    
AUSTRALIA                               http://physics.uwa.edu.au/~paul


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