Is there a faster way to implement a FIFO (queue) ?

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Gurudatha Pai 2012-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/53266-is-there-a-faster-way-to-implement-a-fifo-queue

编辑： Bruno Luong 2022-4-12

Hi, I was wondering if somebody could comment on my use of array indexing. I have a recursive function which uses some initial conditions passed in. I use it in the following manner.

ic = [x_i ic(1:end-1)];

ic is a long vector. x_i is a double.

This line seems to be taking a lot of execution time, about 50% of the total time Matlab spends in this function (using Profiler). The rest of the code is set of vectorized computations; I believe they are as fast as they can be.

I made one small adjustment and it made it a bit faster.

ic(2:end) = ic(1:end-1);
ic(1) = x_i;

This improved the execution time and these two lines take 40% of the total execution time of the function.

Could anybody suggest any better way of implementing this FIFO array.

Thanks for your time and comments.

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Brian Harris 2022-4-12

编辑：Brian Harris 2022-4-12

See this answer: Fast FIFO Array. The circleshift one (which is really just to realign the last answer) is fast because its just a moving pointer "ic=mod(i,Nmax+i)" so doens't move anything. Its really just a circular buffer.

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Answer 1

Bruno Luong 2022-4-12

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https://ww2.mathworks.cn/matlabcentral/answers/53266-is-there-a-faster-way-to-implement-a-fifo-queue#answer_941020

编辑：Bruno Luong 2022-4-12

在 MATLAB Online 中打开

If you don't need to retreive the whole FIFO in order, but read and write element by element, then the best way is NOT rearrange the FIFO buffer

FIFO=nan(1,1000);
n = length(FIFO);
nbreadwrte = 1e6;
% Use index to mark place of the oldest element
tic
for i=1:nbreadwrte
    % readcell
    oldout = FIFO(mod(i-1,n)+1);
    newin = rand(1);
    % write, recent MATLAB do inplace change of internal data
    FIFO(mod(i-1,n)+1) = newin;
end
toc
Elapsed time is 0.125412 seconds.
tic
for i=1:nbreadwrte
    % readcell
    oldout = FIFO(1);
    newin = rand(1);
    % write
    FIFO = [newin FIFO(1:end-1)];
end
toc
Elapsed time is 1.157002 seconds.
for i=1:nbreadwrte
    % readcell
    oldout = FIFO(1);
    newin = rand(1);
    % write
    FIFO(2:end) = FIFO(1:end-1);
    FIFO(1) = newin;
end
toc
Elapsed time is 2.945253 seconds.