For loop Optimization?

Question

denis bertin 2017-9-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/357437-for-loop-optimization

评论： denis bertin 2017-10-13

Hi everybody, i want to optmize(make faster loop) this function:

for k=1:2001
integrando=exp(i*2*pi*var_spaziale(k)*var_spettrale).*funzionefor k=1:N
   integrando=exp(i*2*pi*var_spaziale(k)*var_spettrale).*funzione;
   f(k)=du*sum(integrando);
end

How is it possible to do please?

Many thanks.

3 个评论
显示 1更早的评论隐藏 1更早的评论

denis bertin 2017-10-1

在 MATLAB Online 中打开

Hi everyone,

I have these attached file name: datineltempo_ciclico.m that read file name malta1t.mat,

in th line 95, there is the peace of code like this:

NPF = 942;
N=2001;
v=381x1;(complex numbers)
f=381x1;
t=1x2001;
for(k = 1:NPF)
                        v = datif2(:,k);
                        g = zeros(2001,1);
                        du=f(2)-f(1);
                        for k1=1:N
                           integrando=exp(i*2*pi*t(k1)*f).*v;
                           g(k1)=du*sum(integrando);
                        end
                        v1 = g;
                        v1 = 2 * real(v1);
                        datit(:,k) = v1;
                        %k
                    end
.....

The problem is that is take more time to load the 942*2001 matrix;

Please somebody can i help me optimize(make faster) this loop?

Many thanks.

I need the maximum time reduce execution...

Please Help Me....

denis bertin 2017-10-3

编辑：denis bertin 2017-10-3

Hi,

The modification is to put for example 'tic' and 'toc' in the init and end of code to debug the execution time for all the program.

Now it take too many time to execute. just launch a function call: datineltempo_ciclico.m , then the will open a pop up to select the malta1t.mat file, and enter 0.02. and the execution will start. But is too long time take.

Thank you. If you have another problem to execute it,let me know about please.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jan 2017-10-1

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/357437-for-loop-optimization#answer_283842

编辑：Jan 2017-10-1

在 MATLAB Online 中打开

The exp() function is expensive. So start with avoiding repeated calls with the same argument:

C = exp((2i * pi * t) .* f);    % Auto-expanding, >= R2016b
for k = 1:NPF
  v  = datif2(:,k);
  g  = zeros(2001,1);
  du = f(2)-f(1);
  for k1 = 1:N
     integrando = C(:, k1) .* v;
     g(k1)      = du * sum(integrando);
  end
  datit(:, k) = 2 * real(g);
end

Is datit pre-allocated before the loop? If not, add this.

For Matlab < 2016b:

C = exp(2i * pi * bsxfun(@times, t, f));

Try if this is faster:

C = exp((2i * pi) * t.' .* f.');    % Auto-expaning, >= R2016b
for k = 1:NPF
  du = f(2)-f(1);
  g  = du * C * datif2(:,k);
  datit(:, k) = 2 * real(g);
end

Unfortunately I cannot try this by my own, because your posted code misses the function "interplin". What is it?

6 个评论
显示 4更早的评论隐藏 4更早的评论

denis bertin 2017-10-13

编辑：denis bertin 2017-10-13

在 MATLAB Online 中打开

Hi JAN, Sorry, i check the two Output:

    C = exp((2i * pi * t) .* f);    % Auto-expanding, >= R2016b
for k = 1:NPF
  v  = datif2(:,k);
  g  = zeros(2001,1);
  du = f(2)-f(1);
  for k1 = 1:N
     integrando = C(:, k1) .* v;
     g(k1)      = du * sum(integrando);
  end
  datit(:, k) = 2 * real(g);
end

with:

    C = exp((2i * pi) * t.' .* f.');    % Auto-expaning, >= R2016b
for k = 1:NPF
  du = f(2)-f(1);
  g  = du * C * datif2(:,k);
  datit(:, k) = 2 * real(g);
end

but the two datit matrix are differents.

How is it possible please?

denis bertin 2017-10-13

May be is missing sum(...) function on the second code?

请先登录，再进行评论。

Answer 2

denis bertin 2017-10-3

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/357437-for-loop-optimization#answer_284068

编辑：denis bertin 2017-10-3

Hi JAN SIMON, sorry for this missing information. dammi il passo di misura desiderato? enter: 0.02 . it's all.

The modification is to put for example 'tic' and 'toc' in the init and end of code to debug the execution time for all the program.

Now it take too many time to execute. just launch a function call: datineltempo_ciclico.m , then the will open a pop up to select the malta1t.mat file, and enter 0.02. and the execution will start. But is too long time take.

Thank you. If you have another problem to execute it, i can just rename file italian->to English, this is not a problem.