how to vectorize this for loops?

[Stephen23]

@ Siddhesh Karbhari: please delete the screen shot and give us proper text code. A screen shot is useless to us: we cannot edit it, we cannot run it, we cannot copy-and-paste it into the editor, we cannot do anything with it at all. Please give us real code.

[Adam]

We could type it all out into our editor character by character, hoping we don't make a mistake and that we don't have more useful things to do with our lives :)

[Siddhesh Karbhari]

clc,
octave=3;
lavel=3;
sigma0=sqrt(2);

for i=1:octave
    temp_D=D{i};
    for j=1:level
        scale=sigma0*sqrt(2)^(1/level)^((i-1)*level+j)
        p=(level)*(i-1);
        figure(1);
        subplot(octave,level,p+j);
        f=fspecial('gaussian',[1,floor(6*scale)],scale);
        L1=temp_img;
        if(i==1&&j==1)
            L2=conv2(temp_img,f,'same');
            L2=conv2(L2,f','same');
            temp_D(:,:,j)=L2-L1;
            imshow(uint8(255 * mat2gray(temp_D(:,:,j))));
            L1=L2;
        else
            L2=conv2(temp_img,f,'same');
            L2=conv2(L2,f','same');
            temp_D(:,:,j)=L2-L1;
            L1=L2;
            if(j==level)
                temp_img=L1(2:end-1,2:end-1);
            end
            imshow(uint8(255 * mat2gray(temp_D(:,:,j))));
        end
    end
    D{i}=temp_D;
    temp_img=temp_img(1:2:end,1:2:end);
    temp_img=padarray(temp_img,[1,1],'both','replicate');
end

[Jan]

By the way:

% Simpler:
% sigma0 * sqrt(2) ^ (1/level) ^ ((i-1)*level+j)
  sigma0 * sqrt(2) ^ (i - 1 + j / level)

With a proper indentation the code looks cleaner: Ctrl-A Ctrl-I

Answer 1

[Jan]

Neither the inner nor the outer loop can be vectorized. The two imshow commands are impossible to vectorize. Do you really need them? Do you want a vectorization to increase the speed? Then start with using the profiler to find the most time consuming part of the code.

[Siddhesh Karbhari]

I want to implement this in GPU using MATLAB. What should I do? Can you please guide me?

[Jan]

What do you want to implement on GPU exactly? imshow, subplot, fspecial are not suitable for this, but conv2 will be fine.

[Siddhesh Karbhari]

I want to implement SIFT descriptor on GPU.