function test20
%TEST20 test chol_updown2
%
% Example:
%   test20
% See also: testall

%   Copyright 2006-2007, Timothy A. Davis.
%   http://www.cise.ufl.edu/research/sparse


clear functions

rand ('state', 0) ;
maxerr = [0 0 0 0] ;

for trials = 1:100

    n = fix (100 * rand (1)) ;
    A = rand (n) ;

    if (~ispc)
        if (mod (trials, 2) == 0)
            A = A + 1i*rand(n) ;
        end
    end

    A1 = A*A' + n*eye (n) ;

    try
        L1 = chol (A1)' ;
    catch
        continue ;
    end
    err1 = norm (L1*L1'-A1) ;

    w = rand (n,1) ;

    A2 = A1 + w*w' ;

    L2 = chol (A2)' ;
    err2 = norm (L2*L2'-A2) ;

    % try an update
    L2b = chol_updown2 (L1, +1, w) ;
    err2b = norm (L2b*L2b'-A2) ;

    % try a downdate
    L1b = chol_updown2 (L2, -1, w) ;                                        %#ok
    err1b = norm (L1b*L1b'-A1) ;


    fprintf ('%3d: %6.2e %6.2e : %6.2e %6.2e\n', n, err1, err2, err2b, err1b) ;
    % pause

    maxerr = max (maxerr, [err1 err2 err2b err1b]) ;
end

fprintf ('maxerr: %g\n', maxerr) ;
