How do i make my code faster?

Question

Jelthe 2016-4-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/280208-how-do-i-make-my-code-faster

评论： Brendan Hamm 2016-4-21

Hello,

so i´ve written a code for creating random spectra. It will compute a random spectra between -pi and pi. After one fouriertransformation, a gaussianfilter and one backtransformation i got a 700 x 1 double as my spectra i need. So this basicly works fine. Now i want to have like 9000 times this 700 x 1 spectra in one structure. I made a while loop and a counter to fill every row of the struct with a new created spectra on every new loop. BUT of course it takes like, i assume, an hour to make 9000 of these 700x1 spectra. How can i make my code faster? I think its because matlab has to reread the struct wich is growing with every loop. Is there any good solution to avoid this? enclosed my Code (iam new to matlab, sorry for bad programming):

Sorry for this Big question.

 % Defining Number of Spectra/Event
No_event=700;
No_spectra=10;
% Defining Guassfilter parameter
offset=350;
width=50;
Amplitude=5;
% Defining spectra y-value
randPosPi=-pi;
randNegPi= pi;
% Predefining struct 
k=zeros(1,No_event);
a=1:No_spectra;
c=cell(size(a'));
field = 'spectra';
struct = struct(field,c);
[struct.spectra]=deal(k');
r = 0;
% Guassianfilter
x=1:No_event;
l(x)=Amplitude*exp((-(x-offset).^2)/((2*width)^2));
lstr=l';
% Computing Spectra
while r <= No_spectra
    for spectra=1:No_spectra
    % generating random numbers between -pi and pi
    randomPi = randPosPi + (randNegPi-randPosPi).*rand(No_event,1); %random numbers between -pi and pi
    % Fouriertransformation
    fourier_of_randomPi=fft(randomPi);
    Pi_gauss=lstr.*fourier_of_randomPi;  %guass multiplied with fft of random Pi
    %Pi_gauss_real=lstr.*realteil;
    % Backtransformation
    backfft_randomPi=fft(Pi_gauss);
    Spektrum=lstr.*abs(real(backfft_randomPi));
    % inserting double data from Spektrum into struct
    struct(1+r).spectra=deal(Spektrum);
    end
   r=r+1;       
   if r==(No_spectra);       
       break       
   end

end

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Jelthe 2016-4-21

Thanks guys. Thats really awesome. Right now i am computing 10000 of random spectra in an eyeblink. The only thing that is time wasting is writing all the data into the struct so i get a 10000x1 struct. Any quick tips on that?

thanks again.

Brendan Hamm 2016-4-21

Is there any need to have a struct? You could just store all this data in a pre-allocated matrix.

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Answer 1

Jan 2016-4-21

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/280208-how-do-i-make-my-code-faster#answer_218858

编辑：Jan 2016-4-21

在 MATLAB Online 中打开

If you want to improve the speed of code, find the bottleneck at first. It is useless to improve a part of the code, which uses 0.5% of the total time only. The profiler is the tool for such investigations. I assume fft is the most demanding part, so your code does not matter. Can you reduce the number of fft calls?

Note: Replace this:

r = 0;
while r <= No_spectra
  ...
  r = r+1;       
  if r == (No_spectra);  % Not require, because <= No_spectra is checked also
    break       
  end
end