Neumann boundary condition-matlab code

% Make a function satisfy Neumann boundary condition
1.function g = NeumannBoundCond(f)
2.[nrow,ncol] = size(f);
3.g = f;
4.g([1 nrow],[1 ncol]) = g([3 nrow-2],[3 ncol-2]);  
5.g([1 nrow],2:end-1) = g([3 nrow-2],2:end-1);          
6.g(2:end-1,[1 ncol]) = g(2:end-1,[3 ncol-2]);

What does the codes 4,5,6 mean?

Answer 1

[Youssef El Seblani]

your code is not clear