 LAPACK  3.10.0 LAPACK: Linear Algebra PACKage

◆ zgeqls()

 subroutine zgeqls ( integer M, integer N, integer NRHS, complex*16, dimension( lda, * ) A, integer LDA, complex*16, dimension( * ) TAU, complex*16, dimension( ldb, * ) B, integer LDB, complex*16, dimension( lwork ) WORK, integer LWORK, integer INFO )

ZGEQLS

Purpose:
Solve the least squares problem
min || A*X - B ||
using the QL factorization
A = Q*L
computed by ZGEQLF.
Parameters
 [in] M M is INTEGER The number of rows of the matrix A. M >= 0. [in] N N is INTEGER The number of columns of the matrix A. M >= N >= 0. [in] NRHS NRHS is INTEGER The number of columns of B. NRHS >= 0. [in] A A is COMPLEX*16 array, dimension (LDA,N) Details of the QL factorization of the original matrix A as returned by ZGEQLF. [in] LDA LDA is INTEGER The leading dimension of the array A. LDA >= M. [in] TAU TAU is COMPLEX*16 array, dimension (N) Details of the orthogonal matrix Q. [in,out] B B is COMPLEX*16 array, dimension (LDB,NRHS) On entry, the m-by-nrhs right hand side matrix B. On exit, the n-by-nrhs solution matrix X, stored in rows m-n+1:m. [in] LDB LDB is INTEGER The leading dimension of the array B. LDB >= M. [out] WORK WORK is COMPLEX*16 array, dimension (LWORK) [in] LWORK LWORK is INTEGER The length of the array WORK. LWORK must be at least NRHS, and should be at least NRHS*NB, where NB is the block size for this environment. [out] INFO INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value

Definition at line 120 of file zgeqls.f.

122 *
123 * -- LAPACK test routine --
124 * -- LAPACK is a software package provided by Univ. of Tennessee, --
125 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
126 *
127 * .. Scalar Arguments ..
128  INTEGER INFO, LDA, LDB, LWORK, M, N, NRHS
129 * ..
130 * .. Array Arguments ..
131  COMPLEX*16 A( LDA, * ), B( LDB, * ), TAU( * ),
132  \$ WORK( LWORK )
133 * ..
134 *
135 * =====================================================================
136 *
137 * .. Parameters ..
138  COMPLEX*16 ONE
139  parameter( one = ( 1.0d+0, 0.0d+0 ) )
140 * ..
141 * .. External Subroutines ..
142  EXTERNAL xerbla, ztrsm, zunmql
143 * ..
144 * .. Intrinsic Functions ..
145  INTRINSIC max
146 * ..
147 * .. Executable Statements ..
148 *
149 * Test the input arguments.
150 *
151  info = 0
152  IF( m.LT.0 ) THEN
153  info = -1
154  ELSE IF( n.LT.0 .OR. n.GT.m ) 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, m ) ) 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( 'ZGEQLS', -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 * B := Q' * B
177 *
178  CALL zunmql( 'Left', 'Conjugate transpose', m, nrhs, n, a, lda,
179  \$ tau, b, ldb, work, lwork, info )
180 *
181 * Solve L*X = B(m-n+1:m,:)
182 *
183  CALL ztrsm( 'Left', 'Lower', 'No transpose', 'Non-unit', n, nrhs,
184  \$ one, a( m-n+1, 1 ), lda, b( m-n+1, 1 ), ldb )
185 *
186  RETURN
187 *
188 * End of ZGEQLS
189 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine ztrsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
ZTRSM
Definition: ztrsm.f:180
subroutine zunmql(SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
ZUNMQL
Definition: zunmql.f:167
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