You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cholmod_updown_demo.m
    path of file: ./repos/SuiteSparse/CHOLMOD/MATLAB
    
    the code of the file until where you have to start completion: function cholmod_updown_demo
%CHOLMOD_UPDOWN_DEMO a demo for CHOLMOD's update/downdate & row add/delete
%
% Provides a short demo of CHOLMOD's update/downdate and row add/delete
% functions.
%
% Example:
%   cholmod_updown_demo
%
% See also cholmod_demo

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

fprintf ('\n\n------------------------------------------------------------\n') ;

    
function cholmod_updown_demo
%CHOLMOD_UPDOWN_DEMO a demo for CHOLMOD's update/downdate & row add/delete
%
% Provides a short demo of CHOLMOD's update/downdate and row add/delete
% functions.
%
% Example:
%   cholmod_updown_demo
%
% See also cholmod_demo

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

fprintf ('\n\n------------------------------------------------------------\n') ;
fprintf ('demo of CHOLMOD update/downdate and row add/delete functions\n') ;
fprintf ('------------------------------------------------------------\n\n') ;

% A is the matrix used in the MATLAB 'bench' demo
A = delsq (numgrid ('L', 300)) ;
n = size (A,1) ;
% make b small so we can use absolute error norms, norm (A*x-b)
b = rand (n,1) / n ;

% L*D*L' = A(p,p).  The 2nd argument is zero if A is positive definite.
[LD,ignore,p] = ldlchol (A) ;                                               %#ok

% solve Ax=b using the L*D*L' factorization of A(p,p)
c = b (p) ;
x = ldlsolve (LD, c) ;
x (p) = x ;
err = norm (A*x-b) ;
fprintf ('norm (A*x-b) using ldlsolve:   %g\n', err) ;
if (err > 1e-12)
    error ('!')
end