LAPACK  3.10.1 LAPACK: Linear Algebra PACKage

## ◆ cgeqrs()

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

CGEQRS

Purpose:
Solve the least squares problem
min || A*X - B ||
using the QR factorization
A = Q*R
computed by CGEQRF.
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 array, dimension (LDA,N) Details of the QR factorization of the original matrix A as returned by CGEQRF. [in] LDA LDA is INTEGER The leading dimension of the array A. LDA >= M. [in] TAU TAU is COMPLEX array, dimension (N) Details of the orthogonal matrix Q. [in,out] B B is COMPLEX array, dimension (LDB,NRHS) On entry, the m-by-nrhs right hand side matrix B. On exit, the n-by-nrhs solution matrix X. [in] LDB LDB is INTEGER The leading dimension of the array B. LDB >= M. [out] WORK WORK is COMPLEX 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 119 of file cgeqrs.f.

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 ONE
138  parameter( one = ( 1.0e+0, 0.0e+0 ) )
139 * ..
140 * .. External Subroutines ..
141  EXTERNAL ctrsm, cunmqr, xerbla
142 * ..
143 * .. Intrinsic Functions ..
144  INTRINSIC max
145 * ..
146 * .. Executable Statements ..
147 *
148 * Test the input arguments.
149 *
150  info = 0
151  IF( m.LT.0 ) THEN
152  info = -1
153  ELSE IF( n.LT.0 .OR. n.GT.m ) THEN
154  info = -2
155  ELSE IF( nrhs.LT.0 ) THEN
156  info = -3
157  ELSE IF( lda.LT.max( 1, m ) ) THEN
158  info = -5
159  ELSE IF( ldb.LT.max( 1, m ) ) THEN
160  info = -8
161  ELSE IF( lwork.LT.1 .OR. lwork.LT.nrhs .AND. m.GT.0 .AND. n.GT.0 )
162  \$ THEN
163  info = -10
164  END IF
165  IF( info.NE.0 ) THEN
166  CALL xerbla( 'CGEQRS', -info )
167  RETURN
168  END IF
169 *
170 * Quick return if possible
171 *
172  IF( n.EQ.0 .OR. nrhs.EQ.0 .OR. m.EQ.0 )
173  \$ RETURN
174 *
175 * B := Q' * B
176 *
177  CALL cunmqr( 'Left', 'Conjugate transpose', m, nrhs, n, a, lda,
178  \$ tau, b, ldb, work, lwork, info )
179 *
180 * Solve R*X = B(1:n,:)
181 *
182  CALL ctrsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n, nrhs,
183  \$ one, a, lda, b, ldb )
184 *
185  RETURN
186 *
187 * End of CGEQRS
188 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
subroutine ctrsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
CTRSM
Definition: ctrsm.f:180
subroutine cunmqr(SIDE, TRANS, M, N, K, A, LDA, TAU, C, LDC, WORK, LWORK, INFO)
CUNMQR
Definition: cunmqr.f:168
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