--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolbox/dingdong.m	Thu May 07 18:36:24 2015 +0200
@@ -0,0 +1,15 @@
+function A = dingdong(n)
+%DINGDONG  Dingdong matrix - a symmetric Hankel matrix.
+%          A = DINGDONG(N) is the symmetric N-by-N Hankel matrix with
+%                         A(i,j) = 0.5/(N-i-j+1.5).
+%          The eigenvalues of A cluster around PI/2 and -PI/2.
+
+%          Invented by F.N. Ris.
+%
+%          Reference:
+%          J.C. Nash, Compact Numerical Methods for Computers: Linear
+%          Algebra and Function Minimisation, second edition, Adam Hilger,
+%          Bristol, 1990 (Appendix 1).
+
+p= -2*(1:n) + (n+1.5);
+A = cauchy(p);