parfor loop??? making it faster how?

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Mandar
Mandar 2014-2-28
编辑： Matt J 2014-2-28
i have wrote something like this to search for a color reference in live feed from webcam:
opengl hardware
while (nFrame<z)
b = step(vidobj);
n=0;
yb=size(b,1); %rows
zb=size(b,2); %columns
%u=zeros(zb,2); %------------------------------
v=0;
for g=1:1:yb
for h=1:1:zb
if (b(g,h,1)>=rot_min) && (b(g,h,1)<=rot_max)
n=n+1;
v(n,1)=g;
v(n,2)=h;
end
end
end
v;
%end of rot search
so now i want to exploit the core i5 to use all for cores and make the code even more faster...

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回答（2 个）

Mandar
Mandar 2014-2-28
i know the syntax. here are the probs that i am facing:
here are 2 problems:
a) i can't use the counter 'n' and parfor doesn't allow me to use the index from the earlier loop :O :( please tell me how should i use the parfor to search position of the red reference value!!! :(
b) Also i used the preallocation of v matrix with zeros and at the end i want the final v matrix without zero i.e. with the values other than 0 only. v=(v(v~=0)) works and gives the v matrix in a column matrix. that is not what i want. :(
Please Help!
  1 个评论
Iain
Iain 2014-2-28
1. Put the parfor in the outer loop.
2. You can't use that n in a parfor loop. You may, instead, create "v" to be 2 by yb by zb, and initialised (or set) to NaN when you don't have a valid answer. You can then eliminate the NaNs by
v = reshape(v(~isnan(v),2,[]);
Your problem, however has a faster/simpler solution.
indices = find(b(:,:,1)>= rot_min & b(:,:,1)<=rot_max);
That gets you linear indices to find your qualifying values of b. ind2sub can then be used to return, into a couple of variables (or columns), the rows and column values of the qualifying elements.

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Nitin
Nitin 2014-2-28
you need first to use:
matlabpool open, then use parfor
You will find some nice examples here

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