function A = dif2 ( n )
%
% function A = dif2 ( n )
%
%  Discussion:
%
%    DIF2 sets up the second difference matrix.
%
%  Example:
%
%    N = 5
%
%    A = [ -2  1  0  0  0;
%           1 -2  1  0  0;
%           0  1 -2  1  0;
%           0  0  1 -2  1;
%           0  0  0  1 -2 ]
%
%  Modified:
%
%    14 February 2000
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, integer N, the order of the matrix.  N should be at least 2.
%
%    Output, real A(N,N), the second difference matrix.
%
A =       diag ( ones ( n-1, 1 ), -1 ) ...
  - 2.0 * diag ( ones ( n,   1 ),  0 ) ...
  +       diag ( ones ( n-1, 1 ), +1 );
