Can anyone explain to me what is happening in this 'for' loop?

Question

Rim A. 2017-10-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363841-can-anyone-explain-to-me-what-is-happening-in-this-for-loop

回答： Roger Stafford 2017-10-28

here is my code:

A=[1 2 3;11 12 13];
    for i=A
        A(i(1))=A(i(1))*4;
        disp(i)
        disp (A)
    end

The matrix 'i' is equal to [1;11], then [2;12] and then [3;13]. Why? And why is my final matrix [4 8 3; 44 12 13]? Why are the numbers at (1,1) (1,2) and (1,2) the ones that changed?

Thanks!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Roger Stafford 2017-10-28

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363841-can-anyone-explain-to-me-what-is-happening-in-this-for-loop#answer_288293

在 MATLAB Online 中打开

The “for i=A” line is the source of oddity for your code. It should ordinarily be a row vector - that is, having only one row. As it stands it is sequentially equal to each successive column in A: [1;11], [2;12], [3;13] as you have seen. In the line

A(i(1))=A(i(1))*4;

i(1) is therefore successively 1, 2, then 3, so just the three elements of A: A(1), A(2), and A(3) are multiplied by 4. These are located at (1,1), (2,1), (1,2) in the natural linear order within the matrix A.

I have no idea what you intended for this code but it doesn’t look very useful as it is. If you wanted to multiply each element by 4, just "A = 4*A" would do that.