How to Code with Preallocation, Vectorization and Only Calculating Once

 Hello,

I have a code which needs speeding up and would like to get rid of my loops. How can I do this? I would like to preallocate, vectorize and only calculate it once. The code follows;

figure
for r = 0: 0.4: 3/2
   r;
   k=1;
   for i=0:pi/2:2*pi;
      theta= exp(i);
      for j=0:pi/2:2*pi;
         gamma= exp(j);
         for deltas=i;j;k;
            for t = 0
               deltat= exp (t);
               scatter3(r,theta,gamma,[]);
               hold on
               [i,j,k] = meshgrid(0: 3/2: 2*pi);
            end
         end
      end
   end
end

thank you.

Answer 1

[Jan]

At first look at the MLint messages:

• deltat is not used at all, so omit the line which defines it.
• for t=0 is more expensive than simply set "t = 0;".
• r; wastes time only.
• for deltas=i;j;k is not a valid FOR loop. Perhaps you want: for deltas=[i,j,k], but this is guessed only.

Currently the program is not working correctly. Therefore it is not the time to care about pre-allocation or vectorization.

[jane]

Hi, Thank you very much. I've made all the changes you suggested. the code extracts the data fine and there seems to be no change in the data. At least my scatter3 shows the figure. So I have been mucking about a bit, but not sure if it's at all the correct path. At first glance it looks easy but as i go along, the figures seem to change which is why I'm asking others... I am sure it takes more than just simply placing all the values and vectorising them...

Answer 2

[jane]

I found these links which were quite helpful, but i couldn't really do it correct.

• http://optlab.mcmaster.ca/~yzinchen/fast-matlab-code.pdf
• http://www.mathworks.com/tagteam/70598_91991v00_MATLABApps_WhitePaper.pdf
• http://web.cecs.pdx.edu/~gerry/MATLAB/programming/performance.html