n=A(B) where A and B are matrices?

Question

Abhijith 2013-8-19

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https://ww2.mathworks.cn/matlabcentral/answers/85064-n-a-b-where-a-and-b-are-matrices

采纳的回答： David Sanchez

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Hello, I just tried to do the following operation,

>> B=full(B)

B =

   1     8     3     2     8
   9     8     8     3     6
   1     1     4     2     5
   7     4     9     2     2

>> A=full(A)

A =

   8     2     6     5     9
   3     6     7     1     2
   5     3     7     3     8

>> A(B)

ans =

   1     6     2     4     6
   3     6     6     2     5
   1     1     8     4     3
   2     8     3     4     4

I would like to know what exactly has happened here. Thank you.

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Answer 1

David Sanchez 2013-8-19

2
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https://ww2.mathworks.cn/matlabcentral/answers/85064-n-a-b-where-a-and-b-are-matrices#answer_94569

在 MATLAB Online 中打开

A(B) returns the value of the B(ith) element of A. The elements are counted column-wise, what means than in your case: A(1) = 1; A(2) = 4; A(3) = 2; A(4) = 8; A(5) = 3; ... A(18) = 8;

Now, if you take the matrix B as index, you get back a matrix whose elements are the elements of A in the position determined by the value of the element of B:

B(1) = 5

then, the first element of A(B) = A(5) = 3.

B(2) = 9

then, the second element of A(B) = A(9) = 3

B(3) = 1

then, the second element of A(B) = A(1) = 1

and so on.