LAPACK 3.11.0
LAPACK: Linear Algebra PACKage
Loading...
Searching...
No Matches
zgeqlf.f
Go to the documentation of this file.
1*> \brief \b ZGEQLF
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8*> \htmlonly
9*> Download ZGEQLF + dependencies
10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zgeqlf.f">
11*> [TGZ]</a>
12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zgeqlf.f">
13*> [ZIP]</a>
14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zgeqlf.f">
15*> [TXT]</a>
16*> \endhtmlonly
17*
18* Definition:
19* ===========
20*
21* SUBROUTINE ZGEQLF( M, N, A, LDA, TAU, WORK, LWORK, INFO )
22*
23* .. Scalar Arguments ..
24* INTEGER INFO, LDA, LWORK, M, N
25* ..
26* .. Array Arguments ..
27* COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
28* ..
29*
30*
31*> \par Purpose:
32* =============
33*>
34*> \verbatim
35*>
36*> ZGEQLF computes a QL factorization of a complex M-by-N matrix A:
37*> A = Q * L.
38*> \endverbatim
39*
40* Arguments:
41* ==========
42*
43*> \param[in] M
44*> \verbatim
45*> M is INTEGER
46*> The number of rows of the matrix A. M >= 0.
47*> \endverbatim
48*>
49*> \param[in] N
50*> \verbatim
51*> N is INTEGER
52*> The number of columns of the matrix A. N >= 0.
53*> \endverbatim
54*>
55*> \param[in,out] A
56*> \verbatim
57*> A is COMPLEX*16 array, dimension (LDA,N)
58*> On entry, the M-by-N matrix A.
59*> On exit,
60*> if m >= n, the lower triangle of the subarray
61*> A(m-n+1:m,1:n) contains the N-by-N lower triangular matrix L;
62*> if m <= n, the elements on and below the (n-m)-th
63*> superdiagonal contain the M-by-N lower trapezoidal matrix L;
64*> the remaining elements, with the array TAU, represent the
65*> unitary matrix Q as a product of elementary reflectors
66*> (see Further Details).
67*> \endverbatim
68*>
69*> \param[in] LDA
70*> \verbatim
71*> LDA is INTEGER
72*> The leading dimension of the array A. LDA >= max(1,M).
73*> \endverbatim
74*>
75*> \param[out] TAU
76*> \verbatim
77*> TAU is COMPLEX*16 array, dimension (min(M,N))
78*> The scalar factors of the elementary reflectors (see Further
79*> Details).
80*> \endverbatim
81*>
82*> \param[out] WORK
83*> \verbatim
84*> WORK is COMPLEX*16 array, dimension (MAX(1,LWORK))
85*> On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
86*> \endverbatim
87*>
88*> \param[in] LWORK
89*> \verbatim
90*> LWORK is INTEGER
91*> The dimension of the array WORK. LWORK >= max(1,N).
92*> For optimum performance LWORK >= N*NB, where NB is
93*> the optimal blocksize.
94*>
95*> If LWORK = -1, then a workspace query is assumed; the routine
96*> only calculates the optimal size of the WORK array, returns
97*> this value as the first entry of the WORK array, and no error
98*> message related to LWORK is issued by XERBLA.
99*> \endverbatim
100*>
101*> \param[out] INFO
102*> \verbatim
103*> INFO is INTEGER
104*> = 0: successful exit
105*> < 0: if INFO = -i, the i-th argument had an illegal value
106*> \endverbatim
107*
108* Authors:
109* ========
110*
111*> \author Univ. of Tennessee
112*> \author Univ. of California Berkeley
113*> \author Univ. of Colorado Denver
114*> \author NAG Ltd.
115*
116*> \ingroup complex16GEcomputational
117*
118*> \par Further Details:
119* =====================
120*>
121*> \verbatim
122*>
123*> The matrix Q is represented as a product of elementary reflectors
124*>
125*> Q = H(k) . . . H(2) H(1), where k = min(m,n).
126*>
127*> Each H(i) has the form
128*>
129*> H(i) = I - tau * v * v**H
130*>
131*> where tau is a complex scalar, and v is a complex vector with
132*> v(m-k+i+1:m) = 0 and v(m-k+i) = 1; v(1:m-k+i-1) is stored on exit in
133*> A(1:m-k+i-1,n-k+i), and tau in TAU(i).
134*> \endverbatim
135*>
136* =====================================================================
137 SUBROUTINE zgeqlf( M, N, A, LDA, TAU, WORK, LWORK, INFO )
138*
139* -- LAPACK computational routine --
140* -- LAPACK is a software package provided by Univ. of Tennessee, --
141* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
142*
143* .. Scalar Arguments ..
144 INTEGER INFO, LDA, LWORK, M, N
145* ..
146* .. Array Arguments ..
147 COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )
148* ..
149*
150* =====================================================================
151*
152* .. Local Scalars ..
153 LOGICAL LQUERY
154 INTEGER I, IB, IINFO, IWS, K, KI, KK, LDWORK, LWKOPT,
155 $ MU, NB, NBMIN, NU, NX
156* ..
157* .. External Subroutines ..
158 EXTERNAL xerbla, zgeql2, zlarfb, zlarft
159* ..
160* .. Intrinsic Functions ..
161 INTRINSIC max, min
162* ..
163* .. External Functions ..
164 INTEGER ILAENV
165 EXTERNAL ilaenv
166* ..
167* .. Executable Statements ..
168*
169* Test the input arguments
170*
171 info = 0
172 lquery = ( lwork.EQ.-1 )
173 IF( m.LT.0 ) THEN
174 info = -1
175 ELSE IF( n.LT.0 ) THEN
176 info = -2
177 ELSE IF( lda.LT.max( 1, m ) ) THEN
178 info = -4
179 END IF
180*
181 IF( info.EQ.0 ) THEN
182 k = min( m, n )
183 IF( k.EQ.0 ) THEN
184 lwkopt = 1
185 ELSE
186 nb = ilaenv( 1, 'ZGEQLF', ' ', m, n, -1, -1 )
187 lwkopt = n*nb
188 END IF
189 work( 1 ) = lwkopt
190*
191 IF( lwork.LT.max( 1, n ) .AND. .NOT.lquery ) THEN
192 info = -7
193 END IF
194 END IF
195*
196 IF( info.NE.0 ) THEN
197 CALL xerbla( 'ZGEQLF', -info )
198 RETURN
199 ELSE IF( lquery ) THEN
200 RETURN
201 END IF
202*
203* Quick return if possible
204*
205 IF( k.EQ.0 ) THEN
206 RETURN
207 END IF
208*
209 nbmin = 2
210 nx = 1
211 iws = n
212 IF( nb.GT.1 .AND. nb.LT.k ) THEN
213*
214* Determine when to cross over from blocked to unblocked code.
215*
216 nx = max( 0, ilaenv( 3, 'ZGEQLF', ' ', m, n, -1, -1 ) )
217 IF( nx.LT.k ) THEN
218*
219* Determine if workspace is large enough for blocked code.
220*
221 ldwork = n
222 iws = ldwork*nb
223 IF( lwork.LT.iws ) THEN
224*
225* Not enough workspace to use optimal NB: reduce NB and
226* determine the minimum value of NB.
227*
228 nb = lwork / ldwork
229 nbmin = max( 2, ilaenv( 2, 'ZGEQLF', ' ', m, n, -1,
230 $ -1 ) )
231 END IF
232 END IF
233 END IF
234*
235 IF( nb.GE.nbmin .AND. nb.LT.k .AND. nx.LT.k ) THEN
236*
237* Use blocked code initially.
238* The last kk columns are handled by the block method.
239*
240 ki = ( ( k-nx-1 ) / nb )*nb
241 kk = min( k, ki+nb )
242*
243 DO 10 i = k - kk + ki + 1, k - kk + 1, -nb
244 ib = min( k-i+1, nb )
245*
246* Compute the QL factorization of the current block
247* A(1:m-k+i+ib-1,n-k+i:n-k+i+ib-1)
248*
249 CALL zgeql2( m-k+i+ib-1, ib, a( 1, n-k+i ), lda, tau( i ),
250 $ work, iinfo )
251 IF( n-k+i.GT.1 ) THEN
252*
253* Form the triangular factor of the block reflector
254* H = H(i+ib-1) . . . H(i+1) H(i)
255*
256 CALL zlarft( 'Backward', 'Columnwise', m-k+i+ib-1, ib,
257 $ a( 1, n-k+i ), lda, tau( i ), work, ldwork )
258*
259* Apply H**H to A(1:m-k+i+ib-1,1:n-k+i-1) from the left
260*
261 CALL zlarfb( 'Left', 'Conjugate transpose', 'Backward',
262 $ 'Columnwise', m-k+i+ib-1, n-k+i-1, ib,
263 $ a( 1, n-k+i ), lda, work, ldwork, a, lda,
264 $ work( ib+1 ), ldwork )
265 END IF
266 10 CONTINUE
267 mu = m - k + i + nb - 1
268 nu = n - k + i + nb - 1
269 ELSE
270 mu = m
271 nu = n
272 END IF
273*
274* Use unblocked code to factor the last or only block
275*
276 IF( mu.GT.0 .AND. nu.GT.0 )
277 $ CALL zgeql2( mu, nu, a, lda, tau, work, iinfo )
278*
279 work( 1 ) = iws
280 RETURN
281*
282* End of ZGEQLF
283*
284 END
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine zgeqlf(M, N, A, LDA, TAU, WORK, LWORK, INFO)
ZGEQLF
Definition: zgeqlf.f:138
subroutine zgeql2(M, N, A, LDA, TAU, WORK, INFO)
ZGEQL2 computes the QL factorization of a general rectangular matrix using an unblocked algorithm.
Definition: zgeql2.f:123
subroutine zlarfb(SIDE, TRANS, DIRECT, STOREV, M, N, K, V, LDV, T, LDT, C, LDC, WORK, LDWORK)
ZLARFB applies a block reflector or its conjugate-transpose to a general rectangular matrix.
Definition: zlarfb.f:197
subroutine zlarft(DIRECT, STOREV, N, K, V, LDV, TAU, T, LDT)
ZLARFT forms the triangular factor T of a block reflector H = I - vtvH
Definition: zlarft.f:163