%
%   This script generates a sequence of vectors  a
%   that give increasingly pathological results in
%   computing the Householder transformation with
%   the WRONG CHOICE OF SIGN.
%
%           calls HHbad.m
%
%   D.C. Sorensen
%   15 Sep 04
%
echo on
a = randn(6,1)
[v,tau] = HHbad(a);
Q = eye(6) - tau*v*v';
norm(eye(6) - Q'*Q)

pause

%------------------------------------------------------------------------

theta = 100*sqrt(eps)
a = eye(6,1) + theta*randn(6,1)
[v,tau] = HHbad(a);
Q = eye(6) - tau*v*v';
norm(eye(6) - Q'*Q)


pause

%------------------------------------------------------------------------

theta = sqrt(eps)
a = eye(6,1) + theta*randn(6,1)
[v,tau] = HHbad(a);
Q = eye(6) - tau*v*v';
norm(eye(6) - Q'*Q)


pause


%------------------------------------------------------------------------

theta = sqrt(eps)/100
a = eye(6,1) + theta*randn(6,1)
[v,tau] = HHbad(a);
Q = eye(6) - tau*v*v';
norm(eye(6) - Q'*Q)


pause

%------------------------------------------------------------------------


theta = sqrt(eps)/10000
a = eye(6,1) + theta*randn(6,1)
[v,tau] = HHbad(a);
Q = eye(6) - tau*v*v';
norm(eye(6) - Q'*Q)


echo off