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Re: Direct Memory Replacing in Array

• To: mathgroup at smc.vnet.net
• Subject: [mg46835] Re: Direct Memory Replacing in Array
• From: "Mariusz Jankowski" <mjankowski at usm.maine.edu>
• Date: Tue, 9 Mar 2004 19:57:49 -0500 (EST)
• Organization: University of Southern Maine
• References: <c2k4q5$qq0$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Jeremy, use

mat[[i,j]] = new;

See Part for details.

Mariusz

>>> Jeremy Fox<jeremytfox at yahoo.com> 3/9/2004 5:03:49 AM >>>
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