--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolbox/poisson.m	Thu May 07 18:36:24 2015 +0200
@@ -0,0 +1,14 @@
+function A = poisson(n)
+%POISSON   Block tridiagonal matrix from Poisson's equation (sparse).
+%          POISSON(N) is the block tridiagonal matrix of order N^2
+%          resulting from discretizing Poisson's equation with the
+%          5-point operator on an N-by-N mesh.
+
+%          Reference:
+%          G.H. Golub and C.F. Van Loan, Matrix Computations, second edition,
+%          Johns Hopkins University Press, Baltimore, Maryland, 1989
+%          (Section 4.5.4).
+
+S = tridiag(n,-1,2,-1);
+I = speye(n);
+A = kron(I,S) + kron(S,I);