Matrix with two diagonals: Difference between revisions

<lang Matlab>

function A = diagdiag(N, sparse)

% Create an double-diagonal square matrix

%

% Parameters:

%

% N number of rows (columns)

% sparse should be true to create sparse matrix

%

% Return:

%

% A matrix where all elements A(i, j) are zero except

% elements on the diagonal or the back-diagonal equal 1.

if nargin < 2

sparse = false;

end

if sparse

D = speye(N);

else

D = eye(N);

end

A = D + fliplr(D);

if mod(N, 2) ~= 0

k = fix(N / 2) + 1;

A(k, k) = 1;

end

end

</lang>

{{Output}}

>> diagdiag(7)

ans =

Columns 1 through 6

1 0 0 0 0 0

0 1 0 0 0 1

0 0 1 0 1 0

0 0 0 1 0 0

0 0 1 0 1 0

0 1 0 0 0 1

1 0 0 0 0 0

Column 7

1

0

0

0

0

0

1

>> diagdiag(7, true)

ans =

(1,1) 1

(7,1) 1

(2,2) 1

(6,2) 1

(3,3) 1

(5,3) 1

(4,4) 1

(3,5) 1

(5,5) 1

(2,6) 1

(6,6) 1

(1,7) 1

(7,7) 1