Use vectors to index an 2D array

I have two 1D vectors with X and Y coordinates in 2D array and I want to assign (X,Y) cells some values:

X = [1 2 3 4];

Y = [4 3 2 1];

A(X,Y) = 1;

I.e. want to have only A(1,4), A(2,3), A(3,2) and A(4,1) equal to 1;

But if I run those 3 lines, I have an entire matrix A filled with ones. Of course I can do it in a loop, but I sure it should be the way to vectorize it.

Answer 1

[Star Strider]

Use the sub2ind function to create linear indices from the subscripts:

X = [1 2 3 4];
Y = [4 3 2 1];

A = zeros(4);
Lidx = sub2ind(size(A), X, Y);
A(Lidx) = 1

producing:

A =
     0     0     0     1
     0     0     1     0
     0     1     0     0
     1     0     0     0

.