Finding some numbers in a matrix based on their rows and columns numbers without loop application

Hi, I have a big matrix, lets say A(1375*3600), and another matrix B(600*2), the two numbers of each row in matrix B refer to the location of a cell in matrix A. For example assume that the first row of B is [150 200] and A(150,200)=300; I can use a 'for loop' to find all the 600 elements of matrix A based on matrix B, but I want to know is there any other approach to solve this problem without loop which is too slow? I tried A(B(:,1),B(:,2)); but it did not work.

Answer 1

[Walter Roberson]

idx = sub2ind( size(A), B(:,1), B(:,2) );
A(idx)

More efficient (but not as clear) is

idx = (B(:,2)-1)*size(A,1) + B(:,1);
A(idx)

[Sam]

Thanks alot Walter