MATLAB: N=A(B) where A and B are matrices

matrix manipulation

Hello, I just tried to do the following operation,
>> B=full(B)
B =
     5     1     8     3     2     8
     9     9     8     8     3     6
     1     1     1     4     2     5
     4     7     4     9     2     2
>> A=full(A)
A =
     1     8     2     6     5     9
     4     3     6     7     1     2
     2     5     3     7     3     8
>> A(B)
ans =
     3     1     6     2     4     6
     3     3     6     6     2     5
     1     1     1     8     4     3
     8     2     8     3     4     4
I would like to know what exactly has happened here. Thank you.

Best Answer

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.
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