将Matlab矩阵转换为向量 [英] Converting a matlab matrix to a vector

问题描述

我想在预定义的位置获取Matlab矩阵的元素向量.例如，我有以下

I want to get a vector of elements of a Matlab matrix at predefined locations. For example, I have the following

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

A =

     1     2     3     4
     5     6     7     8
     9    10    11    12
    13    14    15    16

我想要一个向量，该向量将在与i,j相对应的位置为我提供A的值.我尝试过

I want a vector that will give me the values of A at the locations correspongin to i,j. I tried

A(i,j)

ans =

     1     3     4
     5     7     8
     9    11    12

但这不是我想要的.我想得到以下内容

but this is not what I wanted. I want to get the following

>> [A(i(1),j(1)); A(i(2),j(2));A(i(3),j(3))]

ans =

     1
     7
    12

这是什么matlab语法?请避免建议循环或非矢量化形式的任何东西，因为我需要快速完成此工作.希望会有一些内置功能.

What is the matlab syntax for that? Please, avoid suggesting for loops or anything that is not in a vectorized form, as I need this to be done fast. Hopefully there will be some built-in function.

推荐答案

以最快的方式获取它，请使用线性索引:

to get it in the fastest way, use linear indexing:

A((j-1)*size(A,1)+i)

请记住，MATLAB使用列优先顺序.

remember that MATLAB uses a column-major order.

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