136 SUBROUTINE sgelqf( M, N, A, LDA, TAU, WORK, LWORK, INFO )
144 INTEGER info, lda, lwork, m, n
147 REAL a( lda, * ), tau( * ), work( * )
154 INTEGER i, ib, iinfo, iws, k, ldwork, lwkopt, nb,
172 nb =
ilaenv( 1,
'SGELQF',
' ', m, n, -1, -1 )
175 lquery = ( lwork.EQ.-1 )
178 ELSE IF( n.LT.0 )
THEN
180 ELSE IF( lda.LT.max( 1, m ) )
THEN
182 ELSE IF( lwork.LT.max( 1, m ) .AND. .NOT.lquery )
THEN
186 CALL
xerbla(
'SGELQF', -info )
188 ELSE IF( lquery )
THEN
203 IF( nb.GT.1 .AND. nb.LT.k )
THEN
207 nx = max( 0,
ilaenv( 3,
'SGELQF',
' ', m, n, -1, -1 ) )
214 IF( lwork.LT.iws )
THEN
220 nbmin = max( 2,
ilaenv( 2,
'SGELQF',
' ', m, n, -1,
226 IF( nb.GE.nbmin .AND. nb.LT.k .AND. nx.LT.k )
THEN
230 DO 10 i = 1, k - nx, nb
231 ib = min( k-i+1, nb )
236 CALL
sgelq2( ib, n-i+1, a( i, i ), lda, tau( i ), work,
243 CALL
slarft(
'Forward',
'Rowwise', n-i+1, ib, a( i, i ),
244 $ lda, tau( i ), work, ldwork )
248 CALL
slarfb(
'Right',
'No transpose',
'Forward',
249 $
'Rowwise', m-i-ib+1, n-i+1, ib, a( i, i ),
250 $ lda, work, ldwork, a( i+ib, i ), lda,
251 $ work( ib+1 ), ldwork )
261 $ CALL
sgelq2( m-i+1, n-i+1, a( i, i ), lda, tau( i ), work,
subroutine xerbla(SRNAME, INFO)
XERBLA
subroutine sgelqf(M, N, A, LDA, TAU, WORK, LWORK, INFO)
SGELQF
subroutine sgelq2(M, N, A, LDA, TAU, WORK, INFO)
SGELQ2 computes the LQ factorization of a general rectangular matrix using an unblocked algorithm...
integer function ilaenv(ISPEC, NAME, OPTS, N1, N2, N3, N4)
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 slarft(DIRECT, STOREV, N, K, V, LDV, TAU, T, LDT)
SLARFT forms the triangular factor T of a block reflector H = I - vtvH