function W = Wilkinson(n)
%WILKINSON Wilkinson's eigenvalue test matrix.
%   WILKINSON(n) is J. H. Wilkinson's eigenvalue test matrix, Wn+.
%   It is a symmetric, tridiagonal matrix with pairs of nearly,
%   but not exactly, equal eigenvalues.  
%   The most frequently used case is WILKINSON(21).
%   For example, WILKINSON(7) is
%
%          3  1  0  0  0  0  0
%          1  2  1  0  0  0  0
%          0  1  1  1  0  0  0
%          0  0  1  0  1  0  0
%          0  0  0  1  1  1  0
%          0  0  0  0  1  2  1
%          0  0  0  0  0  1  3

%   Copyright 1984-2004 The MathWorks, Inc. 
%   $Revision: 5.7.4.1 $  $Date: 2004/07/05 17:01:30 $

n = double(n);
m = (n-1)/2;
e = ones(n-1,1);
W = diag(abs(-m:m)) + diag(e,1) + diag(e,-1);