Memory for big array which change its data and size in Matlab (buffer)

Question

I am trying to create a buffer (not circle buffer) for big arrays like 100x100 with a specified size.

I can't find any good solution on the internet so i am trying do write it by myself. Here is the code:

In this exa,ple I will be using only small arrays 2x2 and buffer size is 3

A = [1 1; 1 1];
B = [2 2; 2 2];
C = [3 3; 3 3];
buffer = [C B A];
D = [4 4; 4 4];

Now i want to push D and pop A to look like [D C B]

buffer = buffer(1:2,3:6);      %creating [C B]
buffer = [D buffer]            %creating [D C B]

Now the question: What about the A in the memory? Is it still there or it is deleted? If I use about 1000 arrays with size [500x500] with buffer size 3 it would be really bad if I had so much trash in memory. If it is wrong, is there any other way to write such buffer?

With `buffer = [C B A];`, then `buffer = buffer(1:2,3:6);` removes `C`, leaving `buffer` as `[B A]`, is that what you meant or did you want to remove `A` with `buffer = buffer(:,1:4);`? — chappjc, Nov 23 '13 at 02:23

score 1 · Answer 1 · answered Nov 22 '13 at 23:58

1

I would suggest to use a java linked list.

import java.util.LinkedList
q=linkedList()
q.add(A);
q.add(B);
q.add(C);
%get top element
o=q.pop();
%insert new
q.add(D);

Your code requires to copy the whole buffer content, which will be slow for large buffers.

answered Nov 22 '13 at 23:58

Daniel

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Isn't there any matlab(ish) solution ?:) – Tukkan Nov 23 '13 at 00:27

score 1 · Accepted Answer · edited May 23 '17 at 11:56

Your "push front" syntax buffer = [D buffer] seems fine.

As for "push back", you can either concatenate in a similar manner (buffer = [buffer D];) or you can index past the end:

buffer(:,end:end+size(D,2)) = D; % assuming size(D,1) equals size(buffer,1)

For "pop" you either do buffer=buffer(keepRows,keepCols); as in your example, or you can assign [] to whatever indexes you want to remove. For example, given buffer = [C B A];, "pop front" to remove C would be:

buffer(:,1:size(C,2)) = [];

You can remove any values this way, including center elements:

buffer(:,3:4) = []; % remove B from [C B A]

In this way, buffer is rewritten and the removed values are lost. However, the original variable (e.g. B) used to compose buffer remains until you clear it. Keep in mind that when you do buffer = [C B A];, it copies the contents of each variable when doing horizontal concatenation, rather than putting the array in a list.

I once did a pretty thorough comparison of array truncation performance with the v(end-N:end)=[] syntax and the v=v(1:N-1) syntax. Although that is just for a 1D vector, it might be helpful. You may also want to have a look at this article on automatic array growth performance.

Memory for big array which change its data and size in Matlab (buffer)

2 Answers2