function A = ris(n)
%RIS    Symmetric Hankel matrix.
%   A = GALLERY('RIS',N) is a symmetric N-by-N Hankel matrix with 
%   elements A(i,j) = 0.5/(N-i-j+1.5).
%   The eigenvalues of A cluster around PI/2 and -PI/2.
%   This matrix was invented by F.N. Ris.

%   Reference:
%   [1] J.C. Nash, Compact Numerical Methods for Computers: Linear Algebra 
%   and Function Minimisation, second edition, Adam Hilger, Bristol, 
%   1990 (Appendix 1).
%
%   Copyright (c) 1984-98 by The MathWorks, Inc.
%   $Revision: 1.5 $  $Date: 1997/11/21 23:30:00 $

p= -2*(1:n) + (n+1.5);
A = cauchy(p);
