Create a 3D matrix

Question

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?

Answer 1

Create a 3D matrix

A = zeros(20, 10, 3);   %# Creates a 20x10x3 matrix 

Add a 3rd dimension to a matrix

B = zeros(4,4);   C = zeros(size(B,1), size(B,2), 4);  %# New matrix with B's size, and 3rd dimension of size 4 C(:,:,1) = B;                        %# Copy the content of B into C's first set of values 

zeros is just one way of making a new matrix. Another could be A(1:20,1:10,1:3) = 0 for a 3D matrix. To confirm the size of your matrices you can run: size(A) which gives 20 10 3.

There is no explicit bound on the number of dimensions a matrix may have.

Answer 2

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