MATLAB: How to fix the code to produce ones along the reverse diagonal

flipmatrixreverse diagonal

Hi, I am having a problem with my code.

function I = reverse_diag(n)
   I = zeros(n);
   I(1: n+1 : n^2)=1;

I want my code to produce the ones on the reverse diagonal (top right to bottom left). I tried using fliplr because I believe, as of now, this is just a diagonal of ones from top left to bottom right. However, that is not working. Any suggestions?

Best Answer

Assuming you can’t use the eye function, this works:

n = 5;
I = zeros(n);
for k1 = 1:n
    I(k1, end-k1+1) = 1;
end
I =
       0     0     0     0     1
       0     0     0     1     0
       0     0     1     0     0
       0     1     0     0     0
       1     0     0     0     0

EDIT — Added output matrix.

Related Solutions

MATLAB: How to change diagonal element to 1 and set tridiagonal element set to zero

The shown output does not contain 1 on the diagonal, but [1,1,2,2]. Now assume, that the text of the question is, what you want:

A = [1 2 4 5; ...
     5 6 7 8; ...
     1 3 8 9; ...
     0 1 4 5];
s = size(A, 1);
n = numel(A);
A(1:s+1:n)   = 1;   % Called: "linear indexing"
A(2:s+1:n)   = 0;
A(s+1:s+1:n) = 0;
>> A = 
   1     0     4     5
   0     1     0     8
   1     0     1     0
   0     1     0     1

To get the 2s on the half of the diagonal:

A(1:s+1:n)   = [1,1,2,2];

MATLAB: Add a diagonal of zeros to a matrix in MATLAB

You can use a loop like this:

M1 = [ 1 2 3 4 
         2 5 4 2  
         3 4 5 1 
         4 2 1 2 ];
N=size(M1,1);
M2=zeros(N+1,N+1);
for i=0:N-1
    M2 = M2 + diag(diag(M1,-i),-i-1)+ diag(diag(M1,i),i+1);
end
M2

Best Answer

Related Solutions

MATLAB: How to change diagonal element to 1 and set tridiagonal element set to zero

MATLAB: Add a diagonal of zeros to a matrix in MATLAB

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