# Parfor and symmetric matrix

조회 수: 1(최근 30일)
Maria 2021년 8월 12일
편집: Matt J 2021년 8월 13일
Hi,
I need to fill in a matrix. Since it is symmetrical, the two for loops look like this
for i = 1 : m
for j = i : n
operation on the matrix ....
end
end
The other elements of the matrix are filled in by using "permute" (it is a 3D matrix).
I am now modifying the code to make it parallelizable. I tried with the parfor like this
parfor i = 1 : m
for j = i : n
operation on the matrix ....
end
end
At running time, I get the error because matlab does not know the value of "i". I guess this is because the two "for" are not independent.
My question is:
• is there a way to fill in a symmetric matrix by exploiting the symmetry, and using the parfor? Or shall I ignore the symmetry, have the second "for" starting from 1, and getting rid of "permute" ?

댓글을 달려면 로그인하십시오.

### 답변(1개)

Matt J 2021년 8월 12일
편집: Matt J 2021년 8월 12일
[I,J]=ndgrid(1:m,1:n);
keep=J>=I;
I=I(keep);
J=J(keep);
parfor k=1:numel(I)
i=I(k);
j=J(k);
operation on the matrix ....
end
##### 댓글 수: 4표시숨기기 이전 댓글 수: 3
Matt J 2021년 8월 13일
Another possible fix (probably better):
temp = zeros(size(I));
H=0;
parfor k=1:numel(I)
temp(k)=3;
end
idx=sub2ind([m,n],I,J);
H(idx)=temp(:);

댓글을 달려면 로그인하십시오.

R2021a

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!