Improve performance in 'expansion of data' function

1 Ansicht (letzte 30 Tage)
Stephen
Stephen am 15 Jan. 2013
Hi,
In my application i have a performance bottleneck in the following function. I have experimented a little and improved it a bit but im wondering if it can be made any faster. Its right on the edge of acceptable and too slow still.
I need a function to do the following:
if I = [1 2 3 4] then expanding it by 4 would give [1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4]
I am using the data generated from the code below to apply to another set of data
%Expand I and Q Data to longer arrays
%Expands the original data by copying each number a few times
function [I_mod Q_mod] = expandIQ(I,Q,expandfactor)
expandfactor = round(expandfactor);
I_mod = [];
Q_mod = [];
for i=1:expandfactor:(length(I)*expandfactor)
I_mod = [I_mod I((i-1)/expandfactor+1)*ones(1,expandfactor)];
Q_mod = [Q_mod Q((i-1)/expandfactor+1)*ones(1,expandfactor)];
end
if(length(I_mod) ~= length(I)*expandfactor)
error('Unexpected length of I_mod')
end
I have tried 'pre-allocating for speed' as matlab suggested, however this reduced it drastically.
I have been testing the performance using:
I = ones(1,length_of_I);
Q = ones(1,length_of_I);
tic
expandIQ(I,Q,expandfactor);
toc
where length_of_I << expandfactor
eg. length_of_I = 16, expandfactor = 500000 or length_of_I = 500, expandfactor = 50000
Im sure there is a faster way but i can't think of any. I am more comfortable in C than matlab so any suggestions/ideas before i try mex?
Thanks, Stephen
  2 Kommentare
Stephen
Stephen am 15 Jan. 2013
Bearbeitet: Stephen am 15 Jan. 2013
Ahhh, this is much better :) Any improvements on this? Its still a bit slow :/
%Expand I and Q Data to longer arrays
%Expands the original data by copying each number a few times
function [I_mod Q_mod] = expandIQ(I,Q,expandfactor)
expandfactor = round(expandfactor);
I_mod = ones(1,length(I)*expandfactor);
Q_mod = ones(1,length(I)*expandfactor);
for i=1:length(I)
start = (i-1)*expandfactor+1;
I_mod(start:(start+expandfactor-1)) = I(i).*I_mod(start:(start+expandfactor-1));
Q_mod(start:(start+expandfactor-1)) = Q(i).*Q_mod(start:(start+expandfactor-1));
end
if(length(I_mod) ~= length(I)*expandfactor)
error('Unexpected length of I_mod')
end
Matt Kindig
Matt Kindig am 15 Jan. 2013
Bearbeitet: Matt Kindig am 15 Jan. 2013
I haven't tested your code, but I think this is what you are trying to achieve. It seems fairly fast for your length(I)=16, expandfactor = 500000 example:
tic;
I=(1:16);
Y = I'*ones(1,500e3);
Y=reshape(Y',[],1)';
toc %0.087 sec on my machine
% for your second example (length(I)=500, expandfactor = 50e3)
tic;
I=(1:500);
Y = I'*ones(1,50e3);
Y=reshape(Y',[],1)';
toc %0.229 sec on my machine.

Melden Sie sich an, um zu kommentieren.

Akzeptierte Antwort

Cedric
Cedric am 16 Jan. 2013
Hi Stephen,
See if the following brings an improvement in your specific context:
function [I_mod Q_mod] = expandIQ(I,Q,expandfactor)
expandfactor = round(expandfactor) ;
I_mod = reshape(repmat(I, expandfactor, 1), 1, []) ;
Q_mod = reshape(repmat(Q, expandfactor, 1), 1, []) ;
end
It's not too relevant here, but there is a profiler in the Tools menu.
Cheers,
Cedric

Weitere Antworten (0)

Kategorien

Mehr zu Performance and Memory finden Sie in Help Center und File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by