Which MATLAB function can remove the diagonal elements of a NxN matrix
106 views (last 30 days)
Show older comments
Do you know which MATLAB function can do the following work: to remove the diagonal elements of a (N+1)x(N+1) matrix to generate a new NxN matrix.
For say, the old matrix is
[ 0 1 2 3
1 0 2 3
1 2 0 3
1 2 3 0 ]
the generated new matrix is
[ 1 2 3
1 2 3
1 2 3 ]
1 Comment
Kenneth Eaton
on 1 Feb 2011
It's not clear what you are asking. In your example, removing the main diagonal still leaves you with (N+1)*N elements, too many to make an N-by-N matrix. You would have to remove the main diagonal plus either the first superdiagonal or the first subdiagonal to end up with N*N elements.
Accepted Answer
Matt Fig
on 1 Feb 2011
Your example doesn't add up, as Kenneth mentioned. However, in general you could do something like this:
A = [ 0 1 2 3
1 0 2 3
1 2 0 3
1 2 3 0 ];
A(logical(eye(size(A)))) = []; % Or A = A(~eye(size(A)))
A = reshape(A,4,3); % Or 3,4 or whatever.
2 Comments
James Tursa
on 30 Jan 2013
Edited: James Tursa
on 30 Jan 2013
Another variation using linear indexing:
m = size(A,1)+1;
A(1:m:end) = [];
A = reshape(A,4,3); % or whatever
More Answers (3)
Paulo Silva
on 1 Feb 2011
b=triu(a)
b=b(:,2:end)
c=tril(a)
c=c(:,1:end-1)
b+c
1 Comment
ahahahaaron
on 30 Jan 2013
this one produces an overlap and doesn't really produce what the other guy wants.
oren Tadmor
on 12 Jun 2014
Edited: oren Tadmor
on 12 Jun 2014
remove_diagonal = @(t)reshape(t(~diag(ones(1,size(t, 1)))), size(t)-[1 0]);
So :
>> m = magic(5)
m =
17 24 1 8 15
23 5 7 14 16
4 6 13 20 22
10 12 19 21 3
11 18 25 2 9
ans =
23 24 1 8 15
4 6 7 14 16
10 12 19 20 22
11 18 25 2 3
0 Comments
Youssef Khmou
on 31 Jan 2013
Edited: Youssef Khmou
on 31 Jan 2013
hi, Jinlong Wei
According to your example : Here is a function :
function Z=diagrem(X)
N=size(X);
Z=X;
if N(1)~=N(2)
error('Matrix is not square');
end
for x=1:N(1)
Z(x,x)=0;
end
for y=1:N(1)-1
Z(y,y+1)=0;
end
Z(Z==0)=[];
Z=reshape(Z,N(1)-1,N(2)-1);
It produces exactly your example ,it removes R(i,i) and in the second loop it removes R(j,j+1) with 1<=i<=n , 1<=j<n .
1 Comment
Youssef Khmou
on 31 Jan 2013
In case your matrix already contains zeros, then change the code by giving Z(x,x) and Z(y,y+1) a NaN value per example or something else then remove them.
See Also
Categories
Find more on Operating on Diagonal Matrices in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!