166 SUBROUTINE sgehrd( N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO )
173 INTEGER IHI, ILO, INFO, LDA, LWORK, N
176 REAL A( LDA, * ), TAU( * ), WORK( * )
182 INTEGER NBMAX, LDT, TSIZE
183 parameter( nbmax = 64, ldt = nbmax+1,
184 $ tsize = ldt*nbmax )
186 parameter( zero = 0.0e+0,
191 INTEGER I, IB, IINFO, IWT, J, LDWORK, LWKOPT, NB,
211 lquery = ( lwork.EQ.-1 )
214 ELSE IF( ilo.LT.1 .OR. ilo.GT.max( 1, n ) )
THEN
216 ELSE IF( ihi.LT.min( ilo, n ) .OR. ihi.GT.n )
THEN
218 ELSE IF( lda.LT.max( 1, n ) )
THEN
220 ELSE IF( lwork.LT.max( 1, n ) .AND. .NOT.lquery )
THEN
228 nb = min( nbmax, ilaenv( 1,
'SGEHRD',
' ', n, ilo, ihi, -1 ) )
229 lwkopt = n*nb + tsize
234 CALL xerbla(
'SGEHRD', -info )
236 ELSE IF( lquery )
THEN
245 DO 20 i = max( 1, ihi ), n - 1
259 nb = min( nbmax, ilaenv( 1,
'SGEHRD',
' ', n, ilo, ihi, -1 ) )
261 IF( nb.GT.1 .AND. nb.LT.nh )
THEN
266 nx = max( nb, ilaenv( 3,
'SGEHRD',
' ', n, ilo, ihi, -1 ) )
271 IF( lwork.LT.n*nb+tsize )
THEN
277 nbmin = max( 2, ilaenv( 2,
'SGEHRD',
' ', n, ilo, ihi,
279 IF( lwork.GE.(n*nbmin + tsize) )
THEN
280 nb = (lwork-tsize) / n
289 IF( nb.LT.nbmin .OR. nb.GE.nh )
THEN
300 DO 40 i = ilo, ihi - 1 - nx, nb
301 ib = min( nb, ihi-i )
307 CALL slahr2( ihi, i, ib, a( 1, i ), lda, tau( i ),
308 $ work( iwt ), ldt, work, ldwork )
314 ei = a( i+ib, i+ib-1 )
315 a( i+ib, i+ib-1 ) = one
316 CALL sgemm(
'No transpose',
'Transpose',
318 $ ib, -one, work, ldwork, a( i+ib, i ), lda, one,
319 $ a( 1, i+ib ), lda )
320 a( i+ib, i+ib-1 ) = ei
325 CALL strmm(
'Right',
'Lower',
'Transpose',
327 $ one, a( i+1, i ), lda, work, ldwork )
329 CALL saxpy( i, -one, work( ldwork*j+1 ), 1,
336 CALL slarfb(
'Left',
'Transpose',
'Forward',
338 $ ihi-i, n-i-ib+1, ib, a( i+1, i ), lda,
339 $ work( iwt ), ldt, a( i+1, i+ib ), lda,
346 CALL sgehd2( n, i, ihi, a, lda, tau, work, iinfo )
subroutine xerbla(SRNAME, INFO)
XERBLA
subroutine sgehd2(N, ILO, IHI, A, LDA, TAU, WORK, INFO)
SGEHD2 reduces a general square matrix to upper Hessenberg form using an unblocked algorithm.
subroutine sgehrd(N, ILO, IHI, A, LDA, TAU, WORK, LWORK, INFO)
SGEHRD
subroutine slarfb(SIDE, TRANS, DIRECT, STOREV, M, N, K, V, LDV, T, LDT, C, LDC, WORK, LDWORK)
SLARFB applies a block reflector or its transpose to a general rectangular matrix.
subroutine slahr2(N, K, NB, A, LDA, TAU, T, LDT, Y, LDY)
SLAHR2 reduces the specified number of first columns of a general rectangular matrix A so that elemen...
subroutine saxpy(N, SA, SX, INCX, SY, INCY)
SAXPY
subroutine strmm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
STRMM
subroutine sgemm(TRANSA, TRANSB, M, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
SGEMM