function test21
%TEST21 test cholmod2 on diagonal or ill-conditioned matrices
% Example:
%   test21
% See also cholmod_test

% Copyright 2006-2023, Timothy A. Davis, All Rights Reserved.
% SPDX-License-Identifier: GPL-2.0+

fprintf ('=================================================================\n');
fprintf ('test21: test cholmod2 on diagonal or ill-conditioned matrices\n') ;

f = [
 72     % HB/bcsstm22
 315    % Bai/mhdb416
 64     % HB/bcsstm09
 71     % HB/bcsstm21
 1207   % Oberwolfach/t2dal_e
 354    % Boeing/crystm02
 1211   % Oberwolfach/t3dl_e
 ]' ;

for i = f

    Prob = ssget (i)                                                        %#ok
    A = Prob.A ;
    n = size (A,1) ;
    x = ones (n,2) ;
    b = A*x ;
    fprintf ('nnz: %d\n', nnz (A)) ;

    x1 = A\b ;
    x2 = cholmod2 (A,b) ;

    s = norm (A,1) * norm (x,1) + norm (b,1) ;
    resid1 = norm (A*x1-b,1) / s ;
    resid2 = norm (A*x2-b,1) / s ;

    err1 = norm (x-x1,1) ;
    err2 = norm (x-x2,1) ;

    fprintf ('MATLAB  resid %6.1e err %6.1e\n', resid1, err1) ;
    fprintf ('CHOLMOD resid %6.1e err %6.1e\n', resid2, err2) ;
    fprintf ('condest %6.1e\n', condest (A)) ;

end