LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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cgelqs.f
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1*> \brief \b CGELQS
2*
3* =========== DOCUMENTATION ===========
4*
5* Online html documentation available at
6* http://www.netlib.org/lapack/explore-html/
7*
8* Definition:
9* ===========
10*
11* SUBROUTINE CGELQS( M, N, NRHS, A, LDA, TAU, B, LDB, WORK, LWORK,
12* INFO )
13*
14* .. Scalar Arguments ..
15* INTEGER INFO, LDA, LDB, LWORK, M, N, NRHS
16* ..
17* .. Array Arguments ..
18* COMPLEX A( LDA, * ), B( LDB, * ), TAU( * ),
19* $ WORK( LWORK )
20* ..
21*
22*
23*> \par Purpose:
24* =============
25*>
26*> \verbatim
27*>
28*> Compute a minimum-norm solution
29*> min || A*X - B ||
30*> using the LQ factorization
31*> A = L*Q
32*> computed by CGELQF.
33*> \endverbatim
34*
35* Arguments:
36* ==========
37*
38*> \param[in] M
39*> \verbatim
40*> M is INTEGER
41*> The number of rows of the matrix A. M >= 0.
42*> \endverbatim
43*>
44*> \param[in] N
45*> \verbatim
46*> N is INTEGER
47*> The number of columns of the matrix A. N >= M >= 0.
48*> \endverbatim
49*>
50*> \param[in] NRHS
51*> \verbatim
52*> NRHS is INTEGER
53*> The number of columns of B. NRHS >= 0.
54*> \endverbatim
55*>
56*> \param[in] A
57*> \verbatim
58*> A is COMPLEX array, dimension (LDA,N)
59*> Details of the LQ factorization of the original matrix A as
60*> returned by CGELQF.
61*> \endverbatim
62*>
63*> \param[in] LDA
64*> \verbatim
65*> LDA is INTEGER
66*> The leading dimension of the array A. LDA >= M.
67*> \endverbatim
68*>
69*> \param[in] TAU
70*> \verbatim
71*> TAU is COMPLEX array, dimension (M)
72*> Details of the orthogonal matrix Q.
73*> \endverbatim
74*>
75*> \param[in,out] B
76*> \verbatim
77*> B is COMPLEX array, dimension (LDB,NRHS)
78*> On entry, the m-by-nrhs right hand side matrix B.
79*> On exit, the n-by-nrhs solution matrix X.
80*> \endverbatim
81*>
82*> \param[in] LDB
83*> \verbatim
84*> LDB is INTEGER
85*> The leading dimension of the array B. LDB >= N.
86*> \endverbatim
87*>
88*> \param[out] WORK
89*> \verbatim
90*> WORK is COMPLEX array, dimension (LWORK)
91*> \endverbatim
92*>
93*> \param[in] LWORK
94*> \verbatim
95*> LWORK is INTEGER
96*> The length of the array WORK. LWORK must be at least NRHS,
97*> and should be at least NRHS*NB, where NB is the block size
98*> for this environment.
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 complex_lin
117*
118* =====================================================================
119 SUBROUTINE cgelqs( M, N, NRHS, A, LDA, TAU, B, LDB, WORK, LWORK,
120 $ INFO )
121*
122* -- LAPACK test routine --
123* -- LAPACK is a software package provided by Univ. of Tennessee, --
124* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
125*
126* .. Scalar Arguments ..
127 INTEGER INFO, LDA, LDB, LWORK, M, N, NRHS
128* ..
129* .. Array Arguments ..
130 COMPLEX A( LDA, * ), B( LDB, * ), TAU( * ),
131 $ work( lwork )
132* ..
133*
134* =====================================================================
135*
136* .. Parameters ..
137 COMPLEX CZERO, CONE
138 parameter( czero = ( 0.0e+0, 0.0e+0 ),
139 $ cone = ( 1.0e+0, 0.0e+0 ) )
140* ..
141* .. External Subroutines ..
142 EXTERNAL claset, ctrsm, cunmlq, xerbla
143* ..
144* .. Intrinsic Functions ..
145 INTRINSIC max
146* ..
147* .. Executable Statements ..
148*
149* Test the input parameters.
150*
151 info = 0
152 IF( m.LT.0 ) THEN
153 info = -1
154 ELSE IF( n.LT.0 .OR. m.GT.n ) THEN
155 info = -2
156 ELSE IF( nrhs.LT.0 ) THEN
157 info = -3
158 ELSE IF( lda.LT.max( 1, m ) ) THEN
159 info = -5
160 ELSE IF( ldb.LT.max( 1, n ) ) THEN
161 info = -8
162 ELSE IF( lwork.LT.1 .OR. lwork.LT.nrhs .AND. m.GT.0 .AND. n.GT.0 )
163 $ THEN
164 info = -10
165 END IF
166 IF( info.NE.0 ) THEN
167 CALL xerbla( 'CGELQS', -info )
168 RETURN
169 END IF
170*
171* Quick return if possible
172*
173 IF( n.EQ.0 .OR. nrhs.EQ.0 .OR. m.EQ.0 )
174 $ RETURN
175*
176* Solve L*X = B(1:m,:)
177*
178 CALL ctrsm( 'Left', 'Lower', 'No transpose', 'Non-unit', m, nrhs,
179 $ cone, a, lda, b, ldb )
180*
181* Set B(m+1:n,:) to zero
182*
183 IF( m.LT.n )
184 $ CALL claset( 'Full', n-m, nrhs, czero, czero, b( m+1, 1 ),
185 $ ldb )
186*
187* B := Q' * B
188*
189 CALL cunmlq( 'Left', 'Conjugate transpose', n, nrhs, m, a, lda,
190 $ tau, b, ldb, work, lwork, info )
191*
192 RETURN
193*
194* End of CGELQS
195*
196 END
subroutine xerbla(srname, info)
Definition cblat2.f:3285
subroutine cgelqs(m, n, nrhs, a, lda, tau, b, ldb, work, lwork, info)
CGELQS
Definition cgelqs.f:121
subroutine claset(uplo, m, n, alpha, beta, a, lda)
CLASET initializes the off-diagonal elements and the diagonal elements of a matrix to given values.
Definition claset.f:106
subroutine ctrsm(side, uplo, transa, diag, m, n, alpha, a, lda, b, ldb)
CTRSM
Definition ctrsm.f:180
subroutine cunmlq(side, trans, m, n, k, a, lda, tau, c, ldc, work, lwork, info)
CUNMLQ
Definition cunmlq.f:168