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zgshsr.m
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1999-03-05
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# Copyright (C) 1996 A. Scottedward Hodel
#
# This file is part of Octave.
#
# Octave is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2, or (at your option) any
# later version.
#
# Octave is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License
# along with Octave; see the file COPYING. If not, write to the Free
# Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
function x = zgshsr(y)
# x = zgshsr(y)
# apply householder vector based on e^(m) to
# (column vector) y.
# Called by zgfslv
# A. S. Hodel July 24, 1992
# Conversion to Octave by R. Bruce Tenison July 3, 1994
if(!is_vector(y))
error(sprintf("y(%dx%d) must be a vector",rows(y),columns(y)));
endif
x = vec(y);
m = length(x);
if (m>1)
beta = (1 + sqrt(m))*x(1) + sum(x(2:m));
beta = beta/(m+sqrt(m));
x(1) = x(1) - beta*(1.0d0+sqrt(m));
x(2:m) = x(2:m) - beta*ones(m-1,1);
else
x = -x;
endif
endfunction