function A = nma_lap3d(n)
%generate 3D sparse matrix for poisson 3D
% filename: nma_lap3d.m
%
% Function to generate 3D matrix for poisson 3D
% by Nasser M. Abbasi
% based on 2D code by Dr Robert Guy, extended to 3D
%
% INPUT:
% n : Number of internal grid point along one dimension.
% Hence, for n=3, this means there are n^3 unknowns
%
% OUTPUT:
% A: the A matrix to use in solving the 3D problem for
% HW3, problem 3, part(b).
%
L2=nma_lap2d(n,n);
e=ones(n^3,1);
L=spdiags([e e],[-n^2 n^2],n^3,n^3);
Iz=speye(n);
A=kron(Iz,L2)+L;
end