Re: Structures and tensors

[Peter Cloetens]

Hi,

I had similar effects with slow code containing a lot of 3-dimensional arrays. Then I rewrote everything with cells, where each element of the cell array corresponds to 1 matrix. This improved the speed very considerably. 

You use:

E{k}  instead of E(:,:,k)

As long as you do not need to access your data in the third dimension this is much more efficient and readable.

Peter

On Aug 1, 2006, at 5:55 PM, Cédric Févotte wrote:

Hi everyone,

What are the general recommandations about the use of structures and 

tensors in Octave ? Understand, is it recommanded to avoid them ?

What led to my question is the following piece of code, in which I copy 

the vector ones(n,1) sequentially into a variable, which is either

1) a matrix of size n x n_iter,

2) a matrix of size n x n_iter contained in the field of a structure,

3) a tensor of size n x n_iter x 1,

4) a tensor of size n x n_iter x 1 contained in the field of a structure

The results are striking (obtained either on octave 2.1 or 2.9 under 

Linux Debian) :

Elapsed time is 0.071320 seconds.

Elapsed time is 0.324188 seconds.

Elapsed time is 3.279373 seconds.

Elapsed time is 3.327034 seconds.

Any comments ?

All the best

Cedric

%%% Code %%%

n_iter = 10000;

n=50;

%%% 1: Matrix of size n x n_iter %%%

E=zeros(n,n_iter);

tic

for iter=1:n_iter

   E(:,iter)=ones(n,1);

end

toc

%%% 2: Matrix in Structure %%%

cur = struct("E",zeros(n,n_iter));

tic

for iter=1:n_iter

   cur.E(:,iter)=ones(n,1);

end

toc

%%% 3: Tensor of size n x n_iter x 1  %%%

E=zeros(n,n_iter,1);

tic

for iter=1:n_iter

   E(:,iter,1)=ones(n,1);

end

toc

%%% 4: Tensor in Structure %%%

cur = struct("E",zeros(n,n_iter,1));

tic

for iter=1:n_iter

   cur.E(:,iter,1)=ones(n,1);

end

toc

%%% End Code %%%

-- 

Dr Cédric Févotte

Researcher

Mist Technologies

204 rue de Crimée, 75019 Paris, France

Tel: +33 1 55 26 42 31 - Fax: +33 1 55 26 42 03

Web: http://persos.mist-technologies.com/~cfevotte

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