how to stack a 2D matrix form in 3D form?

Could anyone suggest me some hint to solve this problem. i have a 3D matrix A=6*3*6 and length(U)=3 where U values are 3,4,5. I want the updated calculation of A in 3D form. how can we do that?

for j=1:length(U)

M=A(U(j),1,2)* A(:,:,U(j));//stack 1

//stack 2 value will be for the next iteration i.e U(2)=4

//stack 3

How can i get a 6*3*length(U) ?

Answer 1

[DGM]

Something like this

A = randi(9,[6 3 6]);
U = 3:5;

% do it with a loop
M = zeros(size(A,1),size(A,2),numel(U));
for k = 1:length(U)
    M(:,:,k) = A(U(k),1,2) * A(:,:,U(k));
end

Alternatively, this can be vectorized like so:

% if you're running R2016b or newer
M2 = permute(A(U,1,2),[3 2 1]).*A(:,:,U);

% show that this is the same as using the loop
immse(M,M2)

ans = 0

% if you're running R2016a or older
M3 = bsxfun(@times,permute(A(U,1,2),[3 2 1]),A(:,:,U));

% show that this is the same as using the loop
immse(M,M3)

ans = 0