function A = laplacian3d_kron(k)
% LAPLACIAN3D_KRON : discrete Laplace operator in 3 dimensions
%
% A = laplacian3d_kron(k) returns a k^3-by-k^3 sparse matrix


A1 = laplacian1d_sparse(k);
A2 = laplacian2d_kron(k);
I1 = speye(k);
I2 = speye(k^2);

A = kron(I1,A2) + kron(A1,I2);

