Parallel Computing (Job and task)

2012 2 28
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hi i try to run matlab code that runs parallel . my problem is .i have 8 for loops and i want these loops to run at the same time because they are independent .any way to do that.my code is
a=imread('x.jpg');
[xx,yy]=size(a);
while x-1>0 && y-1>0
r=mean-a(x-1,y-1);
x=x-1;
y=y-1;
end
%north
while x-1>0 && y<yy
r=mean-a(x-1,y+1);
x=x-1;
end
%north west
while x-1>0 && y+1<yy
r=mean-a(x-1,y+2);
x=x-1;
y=y+1;
end
%west
while x>0 && y+3<yy
r=mean-a(x+1,y+3);
y=y+1;
end
%north west
while x+3<xx && y+3<yy
r=mean-a(x+3,y+3);
x=x+1;
y=y+1;
end
%norht
while x-1>0 && y-1>0
r=mean-a(x+3,y+1);
x=x-1;
y=y-1;
end
%north east
while x+3<xx && y-1>0
r=mean-a(x+3,y-1);
x=x+1;
y=y-1;
end
%eset
while x>0 && y-1>0
r=mean-a(x+1,y-1);
y=y-1;
end

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 采纳的回答

Walter Roberson
Walter Roberson 2012-2-28

0 个投票

Those loops are not independent: the initial x and y values for any one of the loops depends upon the outcome of the previous loops.
If you want to execute different code per worker, then my understanding is that you would use smpd and use the labindex to switch() to the work to be done. (Or use an array of function handles and index in that by the labindex, I suppose.)
Looking at your code structure, it seems to me likely that the amount of work done would be unbalanced between the workers, with some doing little or no work. There is a high overhead cost to starting a worker, so it is best if each worker does sufficient work that the startup overhead is relatively negligible.
I cannot tell at the moment what your code is intended to do. Please do not use "mean" as a variable name, as it conflicts with the name of the important MATLAB routine mean()

5 个评论
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Isee You
Isee You 2012-2-28
thank u.
but please can you tell me how to use (Job and task)and if it can help me. please can you tell me how?
(smpd)what do you mean by it?
Walter Roberson
Walter Roberson 2012-2-28
Sorry, 'smpd' should have been written 'spmd'.
http://www.mathworks.com/help/toolbox/distcomp/spmd.html
There might be a way to do that work using the Job and Task structure http://www.mathworks.com/help/toolbox/distcomp/bqur7ev-2.html but I don't think that would be the usual way to approach matters.
Isee You
Isee You 2012-2-29
"array of function handles and index in that by the labindex""
i do not familiar with that. any help will be useful !!!
Walter Roberson
Walter Roberson 2012-2-29
See Example 3
http://www.mathworks.com/help/techdoc/ref/function_handle.html
Isee You
Isee You 2012-2-29
can you see my code and tell me your opinion?

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更多回答（1 个）

Isee You
Isee You 2012-2-29

0 个投票

i try this code , do you think it true??
function do_test(avg,x,y)
matlabpool open
a=imread('x.jpg');
% [xx,yy]=size(a);
c = {@northest, @north, @northwest,@west, @southwest, @south,@southeset,@eset};
parfor f=1:8
c{f}(avg,a,x,y) ;
end
function northest(avg,a,x,y)
%north eset
while x-1>0 && y-1>0
r=avg-a(x-1,y-1);
x=x-1;
y=y-1;
end
function north(avg,a,x,y)
[xx,yy]=size(a);
%north
while x-1>0 && y<yy
r=avg-a(x-1,y+1);
x=x-1;
end
function northwest(avg,a,x,y)
[xx,yy]=size(a);
%north west
while x-1>0 && y+1<yy
r=avg-a(x-1,y+2);
x=x-1;
y=y+1;
end
function west(avg,a,x,y)
[xx,yy]=size(a);
%west
while x>0 && y+3<yy
r=avg-a(x+1,y+3);
y=y+1;
end
function southwest(avg,a,x,y)
[xx,yy]=size(a);
%south west
while x+3<xx && y+3<yy
r=avg-a(x+3,y+3);
x=x+1;
y=y+1;
end
function south(avg,a,x,y)
[xx,yy]=size(a);
% south
while x-1>0 && y-1>0
r=avg-a(x+3,y+1);
x=x-1;
y=y-1;
end
function southeset(avg,a,x,y)
[xx,yy]=size(a);
%south east
while x+3<xx && y-1>0
r=avg-a(x+3,y-1);
x=x+1;
y=y-1;
end
function eset(avg,a,x,y)
[xx,yy]=size(a);
%eset
while x>0 && y-1>0
r=avg-a(x+1,y-1);
y=y-1;
end

2 个评论
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Walter Roberson
Walter Roberson 2012-2-29
Well, that code will do something in parallel.
It won't do anything _useful_ as you do not return or store any values in the functions.
It will also not do the equivalent of the serialized code, as in the serialized code, the input of each stage is the output of the previous stage.
But in terms of setting up parallelism... yes, those routines should get executed in parallel.
Isee You
Isee You 2012-2-29
thank u "Walter Roberson".
my code is a step in many steps .

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