Massive matrix, tridiagonal, ones()

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Anastasia Zistatsis 2021-2-15

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https://ww2.mathworks.cn/matlabcentral/answers/746322-massive-matrix-tridiagonal-ones

评论： Anastasia Zistatsis 2021-2-16

I need to transform this matrix, taking the three diagonal lines that have numbers and make them their own matrices. My matrix, however, is 124x124. I do not want to write a 1x123 matrix out that has 122 of the same number and 1 zero. Is there a way use ones() for this?

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Adam Danz 2021-2-15

What 3 diagonal lines?

The description of the data and the description of the goal are not clear.

A demo using a smaller matrix would likely help.

Anastasia Zistatsis 2021-2-15

编辑：Adam Danz 2021-2-15

在 MATLAB Online 中打开

[2 13 0 0 0 0;
2 13 0 0 0;
1 2 13 0 0;
0 1 2 13 0;
0 0 1 2 13];

These are the three diagonals I was talking about: [ 13 13 13 13 13 0], zeros(1,5)*2, and [0 1 1 1 1]

For a much larger matrix, is there a function in matlab that can make it easier to type out the first and third vectors shown above?

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Answer 1

Jan 2021-2-15

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https://ww2.mathworks.cn/matlabcentral/answers/746322-massive-matrix-tridiagonal-ones#answer_624327

在 MATLAB Online 中打开

A = [2 13 0 0 0 0;
     1 2 13 0 0 0;
     0 1 2 13 0 0;
     0 0 1 2 13 0;
     0 0 0 1 2 13];
d1 = diag(A, 0)   % [2 2 2 2 2],'
d2 = diag(A, 1)   % [13 13 13 13 13].'
d3 = diag(A, -1)  % [1 1 1 1].'

I do not understand, how you want to get "[13 13 13 13 13 0]" (especially the trailing 0), "zeros(1,5)*2" (zeros times anything is still zeros?), and [0 1 1 1 1] (again the leading zero)?