Trouble getting array to fill in properly

Question

Michael Eugene Carter 2022-3-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1673404-trouble-getting-array-to-fill-in-properly

回答： Simon Chan 2022-3-17

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