How do I access and modify only the non diagonal entries in a matrix?
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hello.. i hv a question. what is the command to call the non diagonal entries of a matrix? tq very much...
采纳的回答
Rick Rosson
2011-7-28
Please try the following:
M = 8;
N = 5;
X = randn(M,N);
idx = eye(M,N);
Y = (1-idx).*X;
Z = X(~idx);
HTH.
Best, Rick
Responding to your comment:
To multiply the non-diagonal elements by 2, please try:
A = [2 3 5;3 6 8;5 8 4];
idx = eye(size(A));
idx = idx + 2*(1-idx);
Y = idx.*A;
HTH.
Best, Rick
4 个评论
srycandy
2011-7-28
Rick Rosson
2011-7-28
Do you want to keep the diagonal entries as well, or do you want to zero them out? Also, do you want the result to be a 3x3 matrix, or a 6x1 column vector (eliminating the 3 diagonal elements)? Please let me know.
srycandy
2011-7-28
Rick Rosson
2011-7-28
I modified my answer above.
更多回答（4 个）
Nathan Greco
2011-7-28
If tmp is your matrix, try:
tmp-diag(diag(tmp)) %works only with square matrices
OR
triu(tmp,1)+tril(tmp,-1)
Both of these set the diagonal entries to zero, essentially ignoring them. If this isn't what you want, please clarify.
5 个评论
srycandy
2011-7-28
srycandy
2011-7-28
Nathan Greco
2011-7-28
You could either do the above methods and multiply (.*) the result by 2, or use indexing as such:
idx = find(~eye(size(A))); %get NON diagonal entries
A(idx) = A(idx).*2;
Nathan Greco
2011-7-28
OR: A.*2-diag(diag(A)) would work.
srycandy
2011-7-28
dor eivensitz
2017-11-2
0 个投票
i want to keep both diagonal in matrix size i don't know, defined by n, and all other elements to multiply by them self plus 1. tnx
1 个评论
James Tursa
2017-11-2
Please open up a new question for this, and provide a short example in that new question.
James Tursa
2017-11-2
Another way for a square matrix:
M = your matrix
x = ~logical(eye(size(M)));
M(x) = 2*M(x); % <-- or whatever function you want on the rhs using M(x)
Niba Kainat
2024-7-18
0 个投票
hi can someone tell me how to compute sum of no diagonal entries.
1 个评论
M = magic(4) % some square matrix
idx = ~eye(size(M)) % logical index indicating non-diagonal entries
result = sum(M(idx),'all') % sum the non-diagonal entries
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