Creating a Tridiagonal Matrix with varying values

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Hello, I am trying to create a tridiagonal matrix with varying values. As shown in the image below

the main diagonal is able to have varying value, but the code only works if the offsetting diagonals are constant values. I am attempting to have all 3 diagonals be varying numerals any help would be greatly appreciated. I will attach my code below.

function [A,b] = ok(k,m)
A=[k];
n=size(A,2)
b=[m];
if size(b,2) < 1
    b=[m];
else
    b=[m]';
j=size(b,2);
end
N = n;
a = -k;
d =4;
c =4;
M = zeros(N,N)
M(  1:1+N:N*N) = a
M(N+1:1+N:(N*N)-1) = d
M(  2:1+N:N*N-N) = c