Need help for vectorization?

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reshdev
reshdev 2014-9-5
评论： Guillaume 2014-9-6
Hello
This program is running very slow. Can anyone please help me to make it fast like by vectorizing this code.
Thanks
Note that---Pop_Size,n,dr,f,S,T are my inputs. i am giving f,S,T input as matrix like[f S T]
for u= 1:Pop_Size
ridx = 1;
c=n-1;
output = zeros(n,n*dr);
for z = 1:n:n*dr
M = zeros(c);
f = inputData(ridx,1); % f= Demand
S = inputData(ridx,2); % S= Source node
T = inputData(ridx,3); % T= Termination node
ridx = ridx + 1;
for k = 1:f
p = randperm(c);
for s = 1:c
M(p(s),s) = M(p(s),s) + 1;
end
end
M = [M(:,1:S-1),zeros(c,1),M(:,S:c)]; % Add column of zeros
M = [M(1:T-1,:);zeros(1,c+1);M(T:c,:)];% Add row of zeros
M(1:(c+2):(c+1)*(c+1))= 0;
output(:, z:z+c) = M;
end
outp(:,:,u) = output(:,:); %To save all the chromosomes
fprintf('Chromosome %d\n',u);
disp(output);
end

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回答（2 个）

Roger Stafford
Roger Stafford 2014-9-5
编辑：Roger Stafford 2014-9-5
In your Aug. 20 Answers #151724 article "Please help me to modify the following program" I showed how you could replace all your current code that creates the M matrix with just three lines of code using the 'accumarray' function. It replaces two nested for-loops. This could possibly improve your execution time. Why don't you try it?
  1 个评论
Guillaume
Guillaume 2014-9-6
If output is significantly large, then, yes, the resizing of outp will slow down your program as matlab has to copy the whole content into a new memory slot each time. You can:
Either, predeclare outp:
outp = zeros(n, n*dr, Pop_Size);
Or store output into a cell array:
outp{u} = output;

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Guillaume
Guillaume 2014-9-5
I'm not sure there's much that can be vectorised in there. An alternative for your for k loop could be:
coloffset = 0:c:c^2-1;
for k = 1:f
indices = randi(c, 1, c) + coloffset;
M(indices) = M(indices) + 1;
end
But on my machine it's only faster for c>70.
The insertion of a row and column of zero is going to be expensive, so instead I would do:
M = zeros(c+1); %i.e. M = zeros(n);
%randomly add 1 to a row of column 1:n, but never in last row, using whichever method
%with your method change s to go from 1:n (but p still randperm(c))
%with mine change randi to be randi(c, 1, n) and coloffset to be 0:n:n^2-1
M(:, S) = 0; %set column to 0
M(end, :) = M(T, :); %swap row T with last row
M(T, :) = 0;
Finally, you could change setting the diagonal to 0 to:
M(logical(eye(n)) = 0;
Don't know if it's faster.

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