Find values of a specific page of a 3d matrix at specific positions

I have two matrices (A and B). A is a 2D matrix (3x3) which defins some zones (1, 2, and 3).

   A= 

      1 1 1

      2 2 2

      3 3 3

B is a 3D matrix (3x3x2) like:

   B(:,:,1)

      1 2 1

      2 1 2

      1 1 2

   B(:,:,2)

      2 2 2

      1 1 2

      2 2 1

I would like to find the indices (rows, and columns, or linear indices) of B, when B equals (e.g.) 2 only in (e.g.) page 1, and only in (e.g.) zone 2.

I tried this, but it didn't do the job:

   [rA_2 cA_2]= find(A==2);

   [r0B_2 c0B_2]= ind2sub(size(B),find(B(rA_2,cA_2,1)==2);

I seem not to find a solution for what I thought to be a quite simple task.

Answer 1

[Adam]

pageIdx = find( B(:,:,pageNo) == 2 & A == zoneNo );

idx = pageIdx + 9 * ( pageNo - 1 );

should work I think. First find the indices on the chosen page, then add the indices for all previous pages to that (i.e. there are 9 indices per page previous to the chosen one).

[Umberto Minora]

Yep, it did the job. Thanks! Anyway, for a more generic use, I woul do idx = pageIdx + numel(A)*(pageNo-1);

Moreover, to find rows and columns (instead of linear indices) one would do [r c]= ind2sub(size(B),pageIdx+numel(A)*(pageNo-1))

[Adam]

Well if you only want rows and columns on the given page then you can ignore all the stuff with adding page numbers and just use:

[r, c] = find( B(:,:,pageNo) == 2 & A == zoneNo );