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MathGroup Archive 2004

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RE: Direct Memory Replacing in Array

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46833] RE: [mg46823] Direct Memory Replacing in Array
  • From: "David Park" <djmp at earthlink.net>
  • Date: Tue, 9 Mar 2004 19:57:46 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Jeremy,

I think the following works.

matrix = {{a1, b1, c1}, {a2, b2, c2}};

Part[matrix, 2, 2] = b2new
b2new

matrix
{{a1, b1, c1}, {a2, b2new, c2}}

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/ 



From: Jeremy Fox [mailto:jeremytfox at yahoo.com]
To: mathgroup at smc.vnet.net

The Mathematica syntax 

mat = ReplacePart[mat,new,index]

is clean. However, it probably involves a complete replacing of the
entire, old mat with the entire new mat, in memory. This operation is
expensive if the user is interested in changing only a small part of a
large array mat.

Is there a way to change small numbers of elements in an array without
requiring the other elements to be copied again? This is how low-level
languages such a C and Fortran work.

Jeremy



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