148 SUBROUTINE cgehd2( N, ILO, IHI, A, LDA, TAU, WORK, INFO )
155 INTEGER IHI, ILO, INFO, LDA, N
158 COMPLEX A( LDA, * ), TAU( * ), WORK( * )
165 parameter( one = ( 1.0e+0, 0.0e+0 ) )
175 INTRINSIC conjg, max, min
184 ELSE IF( ilo.LT.1 .OR. ilo.GT.max( 1, n ) )
THEN
186 ELSE IF( ihi.LT.min( ilo, n ) .OR. ihi.GT.n )
THEN
188 ELSE IF( lda.LT.max( 1, n ) )
THEN
192 CALL xerbla(
'CGEHD2', -info )
196 DO 10 i = ilo, ihi - 1
201 CALL clarfg( ihi-i, alpha, a( min( i+2, n ), i ), 1, tau( i ) )
206 CALL clarf(
'Right', ihi, ihi-i, a( i+1, i ), 1, tau( i ),
207 $ a( 1, i+1 ), lda, work )
211 CALL clarf(
'Left', ihi-i, n-i, a( i+1, i ), 1,
212 $ conjg( tau( i ) ), a( i+1, i+1 ), lda, work )
subroutine xerbla(SRNAME, INFO)
XERBLA
subroutine cgehd2(N, ILO, IHI, A, LDA, TAU, WORK, INFO)
CGEHD2 reduces a general square matrix to upper Hessenberg form using an unblocked algorithm.
subroutine clarf(SIDE, M, N, V, INCV, TAU, C, LDC, WORK)
CLARF applies an elementary reflector to a general rectangular matrix.
subroutine clarfg(N, ALPHA, X, INCX, TAU)
CLARFG generates an elementary reflector (Householder matrix).