121 parameter( two = 2.0e+0, one = 1.0e+0, zero = 0.0e+0 )
125 REAL BETA, BIGNUM, SAVEALPHA, SMLNUM, XNORM
128 REAL SLAMCH, SLAPY2, SNRM2
129 EXTERNAL slamch, slapy2, snrm2
144 xnorm = snrm2( n-1, x, incx )
146 IF( xnorm.EQ.zero )
THEN
150 IF( alpha.GE.zero )
THEN
160 x( 1 + (j-1)*incx ) = 0
168 beta = sign( slapy2( alpha, xnorm ), alpha )
169 smlnum = slamch(
'S' ) / slamch(
'E' )
171 IF( abs( beta ).LT.smlnum )
THEN
175 bignum = one / smlnum
178 CALL sscal( n-1, bignum, x, incx )
181 IF( (abs( beta ).LT.smlnum) .AND. (knt .LT. 20) )
186 xnorm = snrm2( n-1, x, incx )
187 beta = sign( slapy2( alpha, xnorm ), alpha )
191 IF( beta.LT.zero )
THEN
195 alpha = xnorm * (xnorm/alpha)
200 IF ( abs(tau).LE.smlnum )
THEN
209 IF( savealpha.GE.zero )
THEN
214 x( 1 + (j-1)*incx ) = 0
223 CALL sscal( n-1, one / alpha, x, incx )
subroutine slarfgp(N, ALPHA, X, INCX, TAU)
SLARFGP generates an elementary reflector (Householder matrix) with non-negative beta.
subroutine sscal(N, SA, SX, INCX)
SSCAL