how to find value in matrix based on specified location

Question

Yu Li 2022-12-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1880282-how-to-find-value-in-matrix-based-on-specified-location

编辑： DGM 2022-12-17

Hi:

I have a matrix and I want to cite the value at specified locaiton, the inputs is not specified row or colume, but the row-id and colume-id, for example:

A=[1,2,3,4;
    5,6,7,8;
    9,10,11,12;
    13,14,15,16];

I want the cite the value at row=2, column=3, and row=3, colume=3

I tried command:

A([2,3],[3,3])
ans = 2×2
     7     7
    11    11

the output is a 2*2 matrix, instead of 7, 11.

is there anyway to make the output to be 7 and 11?

Thanks!

Yu

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Answer 1

DGM 2022-12-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1880282-how-to-find-value-in-matrix-based-on-specified-location#answer_1130162

编辑：DGM 2022-12-17

在 MATLAB Online 中打开

When you select A([2,3],[3,3]), you're selecting four points. It's easier to understand in this case:

A = [1,2,3,4;
    5,6,7,8;
    9,10,11,12;
    13,14,15,16];
A([1 4],[1 4])
ans = 2×2
     1     4
    13    16

Note that you're selecting the intersection of the specified rows and columns. Since there are two each, there are four elements being selected.

The way around this ambiguity is to use linear indexing

A = [1,2,3,4;
    5,6,7,8;
    9,10,11,12;
    13,14,15,16];
% convert to linear index
idx = sub2ind(size(A),[2,3],[3,3]);
% index into A
A(idx)
ans = 1×2
     7    11