How do I convert a 2X2 matrix to 4X4 matrix in MATLAB?

Question

I need some help in converting a 2X2 matrix to a 4X4 matrix in the following manner:

A = [2 6;
     8 4]

should become:

B = [2 2 6 6;
     2 2 6 6;
     8 8 4 4;
     8 8 4 4]

How would I do this?

Answer 1

There is a Reshape() function that allows you to do this...

For example:

reshape(array, [64, 16])

And you can find a great video tutorial here

Cheers

Answer 2

This works:

A = [2 6; 8 4];
[X,Y] = meshgrid(1:2);
[XI,YI] = meshgrid(0.5:0.5:2);
B = interp2(X,Y,A,XI,YI,'nearest');

This is just two-dimensional nearest-neighbor interpolation of A(x,y) from x,y ∈ {1,2} to x,y ∈ {0.5, 1, 1.5, 2}.

Edit: Springboarding off of Jason S and Martijn's solutions, I think this is probably the shortest and clearest solution:

A = [2 6; 8 4];
B = A([1 1 2 2], [1 1 2 2]);

Answer 3

A = [2 6; 8 4];
% arbitrary 2x2 input matrix

B = repmat(A,2,2);
% replicates rows & columns but not in the way you want

B = B([1 3 2 4], :);
% swaps rows 2 and 3

B = B(:, [1 3 2 4]);
% swaps columns 2 and 3, and you're done!

Answer 4

Can be done even easier than Jason's solution:

B = A([1 1 2 2], :);
B = B(:, [1 1 2 2]);

Answer 5

Here's one more solution:

A = [2 6; 8 4];
B = A( ceil( 0.5:0.5:end ), ceil( 0.5:0.5:end ) );

which uses indexing to do everything and doesn't rely on the size or shape of A.

Answer 6

Here's an even shorter solution which uses the MATLAB functions KRON and ONES:

>> A = [2 6; 8 4];
>> B = kron(A,ones(2))

B =

     2     2     6     6
     2     2     6     6
     8     8     4     4
     8     8     4     4