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Re: 2D matrixes into a 3D matrix

From: David Bateman
Subject: Re: 2D matrixes into a 3D matrix
Date: Mon, 29 Jan 2007 21:39:36 +0100
User-agent: Thunderbird (X11/20060921)

Andres Sepulveda wrote:
>  Hi,
>  I want to "stick" a series of 2D (e.g. 2x2) matrixes into a  3D matrix 
> (2x2xN) with N increasing as I stick a new matrix.
> Is it better to define a large-enough 3D matrix and then reduce its size?
>        Andres

I have no idea what you mean from the above statement. If you know the
final size of the 3D matrix, then yes it is better to preallocate the
memory something like

A = zeros([2,2,N]);
for i=1:N
  A(:,:,i)= randn(2,2);

is definitely an advantage, though the above example is artificial and
should be written as A = randn([2,2,2]) instead. Note that is you can
vector the code as do without the loop to create the matrix, you are
much better off without it...


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