Trouble getting array to fill in properly

I am trying to fill in a tridiagonal 8x8 array using a for loop. I believe that most of the array is flling in properly, but there are four of the array numbers that are being filled in as zero and I can't figure out how to fix it. This is the code that I have for it so far.

x = [0.06 0.47 1.01 1.50 2.05 2.53 2.99 3.44];
y = [1.0499 1.3274 1.3588 1.2550 1.6322 2.5523 3.4462 3.6684];
z = linspace(x(1),x(end),1000);
n = length(x)-1;
h = zeros(n,1);
A = zeros(n+1,n+1);
for i=1:n
    h(i)=x(i+1)-x(i);
end
for i=2:n
    for k=2:n
        if i==k
            A(i,k)=2*(h(i-1)+h(i));
        elseif (k+1)==i
            A(i,k)=h(i-1);
        elseif (k-1)==i
            A(i,k)=h(i);
        else 
            A(i,k)=0;
        end
    end
    A(1,1)=1;
    A(n+1,n+1)=1;
end

The problem that I am having is the I think there is something wrong with the code that prevents it from properly filling in A(1,2) A(2,1) A(7,8) and A(8,7), but I don't know what would cause that to happen, this is the matrix that I am getting when I run this, and you can see that the corners of the matrix aren't filled in correctly.

A =

1.0000 0 0 0 0 0 0 0

0 1.9000 0.5400 0 0 0 0 0

0 0.5400 2.0600 0.4900 0 0 0 0

0 0 0.4900 2.0800 0.5500 0 0 0

0 0 0 0.5500 2.0600 0.4800 0 0

0 0 0 0 0.4800 1.8800 0.4600 0

0 0 0 0 0 0.4600 1.8200 0

0 0 0 0 0 0 0 1.0000

Answer 1

[Simon Chan]

The for loop starts from 2 to n, which is 7 in your case.

However, the matrix has 8 rows and 8 columns and hence you never touch the first column, first row, last column and last row in the loop.

At the end, you just fill in the following two values and hence it appears in the output. (Actually no need to put these 2 lines inside the for loop)

A(1,1)=1;
A(n+1,n+1)=1;