How to Assemble the matrix shown in the image on Matlab for any number of nodes?

[Stephen23]

OP continued the same question here:

http://www.mathworks.com/matlabcentral/answers/265649-how-to-assemble-this-matrix-below-with-this-pattern-for-any-number-of-nodes-n

[Rena Berman]

(Answers dev) Restored question.

Answer 1

[Walter Roberson]

n = 4;    %for example

main_diagonal = [ [-4, repmat(-3,1,n-2), -4], repmat([-5, repmat(-4,1,n-2), -5], 1, 2), [-6, repmat(-5,1,n-2), -6] ];
N = length(main_diagonal);

m = diag(ones(1, N-4), -4) +
    diag(ones(1, N-1), -1) +
    diag(main_diagonal) +
    diag(ones(1, N-1), 1) +
    diag(ones(1, N-4), -4)

Answer 2

[Guillaume]

There is not enough information to know how to construct the main diagonal, but you can just sum a bunch of diag:

m = diag(ones(1, 12), -4) + ...
    diag(ones(1, 15), -1) + ...
    diag([-4 -3 -3 -4 -5 -4 -4 -5 -5 -4 -4 -5 -6 -5 -5 -6], 0) + ... %no idea what the pattern is
    diag(ones(1, 15), 1) + ...
    diag(ones(1, 12), 4)

[amar]

I want to assemble this matrix for any number of nodes 'n'

[Walter Roberson]

main_diagonal = [-4 -3 -3 -4 -5 -4 -4 -5 -5 -4 -4 -5 -6 -5 -5 -6];  %we do not know the rule for this
n = length(main_diagonal);
m = diag(ones(1, n-4), -4) +
    diag(ones(1, n-1), -1) +
    diag(main_diagonal) +
    diag(ones(1, n-1), 1) +
    diag(ones(1, n-4), -4)