How to index with a changing index

Question

xiaojuezi 2021-12-8

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1606435-how-to-index-with-a-changing-index

回答： DGM 2021-12-8

Hi, I would like to construct a matrix L of size nxn that looks like below:

L = [a,b,c,0,0,0,0,...
     0,a,b,c,0,0,0,...
     0,0,a,b,c,0,0,...
     0,0,0,a,b,c,0,...
     ...
     0,0,0,0,...a,b,c];

I'm trying to do this without the for loop.

 i = 2:n-1;
 L(:,i-1:i+1) = repmat([a,b,c],n,1);

However, this doesn't give what I want, and I was warned by the complier that i is a non-scalar operator.

Is there a way to fix this?

Thank you very much!

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Answer 1

DGM 2021-12-8

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1606435-how-to-index-with-a-changing-index#answer_850775

在 MATLAB Online 中打开

You can try something like this:

a = 1;
b = 2;
c = 3;
A = toeplitz([a 0 0 0 0 0 0],[a b c 0 0 0 0]);
A = A(1:end-2,:)
A = 5×7
     1     2     3     0     0     0     0
     0     1     2     3     0     0     0
     0     0     1     2     3     0     0
     0     0     0     1     2     3     0
     0     0     0     0     1     2     3