M is a 3-D matrix.
M(:,:,1) = Hphi;
Means set the first "page" of the 3rd dimension equal to the output of Heaviside with inputs phi and epsilon, which here is Hphi.
M(:,:,2) = 1-Hphi;
Means set the second "page" of the 3rd dimension equal to 1-Hphi.
In general, M(:,:,index) is the way of assigning all rows and all columns of the index-th page of a 3D matrix a given value.
For example:
M = zeros(2,2,2); % M is 2x2x2
M(:,:,1) = 1;
M(:,:,2) = 2;
Now M(:,:,1) is a 2x2 matrix of ones and M(:,:,2) is a 2x2 matrix of 2s.
N_class = size(M,3);
Is just returning the size of M in the 3rd dimension
M = ones(2,2,4);
size(M,3)
Are you trying to read the Matlab documentation?
