[matlab] Create a 3D matrix

How can I define a 3D matrix in MATLAB?

For example a matrix of size (8 x 4 x 20) or add a 3rd dimension to an existing 2D matrix?

If you want to define a 3D matrix containing all zeros, you write

A = zeros(8,4,20);

All ones uses ones, all NaN's uses NaN, all false uses false instead of zeros.

If you have an existing 2D matrix, you can assign an element in the "3rd dimension" and the matrix is augmented to contain the new element. All other new matrix elements that have to be added to do that are set to zero.

For example

B = magic(3); %# creates a 3x3 magic square
B(2,1,2) = 1; %# and you have a 3x3x2 array

I use Octave, but Matlab has the same syntax.

Create 3d matrix:

octave:3> m = ones(2,3,2)
m =

ans(:,:,1) =

   1   1   1
   1   1   1

ans(:,:,2) =

   1   1   1
   1   1   1

Now, say I have a 2D matrix that I want to expand in a new dimension:

octave:4> Two_D = ones(2,3)
Two_D =
   1   1   1
   1   1   1

I can expand it by creating a 3D matrix, setting the first 2D in it to my old (here I have size two of the third dimension):

octave:11> Three_D = zeros(2,3,2)
Three_D =

ans(:,:,1) =

   0   0   0
   0   0   0

ans(:,:,2) =

   0   0   0
   0   0   0



octave:12> Three_D(:,:,1) = Two_D
Three_D =

ans(:,:,1) =

   1   1   1
   1   1   1

ans(:,:,2) =

   0   0   0
   0   0   0