LAPACK  3.6.1 LAPACK: Linear Algebra PACKage
 subroutine sgetrs ( character TRANS, integer N, integer NRHS, real, dimension( lda, * ) A, integer LDA, integer, dimension( * ) IPIV, real, dimension( ldb, * ) B, integer LDB, integer INFO )

SGETRS

Purpose:
``` SGETRS solves a system of linear equations
A * X = B  or  A**T * X = B
with a general N-by-N matrix A using the LU factorization computed
by SGETRF.```
Parameters
 [in] TRANS ``` TRANS is CHARACTER*1 Specifies the form of the system of equations: = 'N': A * X = B (No transpose) = 'T': A**T* X = B (Transpose) = 'C': A**T* X = B (Conjugate transpose = Transpose)``` [in] N ``` N is INTEGER The order of the matrix A. N >= 0.``` [in] NRHS ``` NRHS is INTEGER The number of right hand sides, i.e., the number of columns of the matrix B. NRHS >= 0.``` [in] A ``` A is REAL array, dimension (LDA,N) The factors L and U from the factorization A = P*L*U as computed by SGETRF.``` [in] LDA ``` LDA is INTEGER The leading dimension of the array A. LDA >= max(1,N).``` [in] IPIV ``` IPIV is INTEGER array, dimension (N) The pivot indices from SGETRF; for 1<=i<=N, row i of the matrix was interchanged with row IPIV(i).``` [in,out] B ``` B is REAL array, dimension (LDB,NRHS) On entry, the right hand side matrix B. On exit, the solution matrix X.``` [in] LDB ``` LDB is INTEGER The leading dimension of the array B. LDB >= max(1,N).``` [out] INFO ``` INFO is INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value```
Date
November 2011

Definition at line 123 of file sgetrs.f.

123 *
124 * -- LAPACK computational routine (version 3.4.0) --
125 * -- LAPACK is a software package provided by Univ. of Tennessee, --
126 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
127 * November 2011
128 *
129 * .. Scalar Arguments ..
130  CHARACTER trans
131  INTEGER info, lda, ldb, n, nrhs
132 * ..
133 * .. Array Arguments ..
134  INTEGER ipiv( * )
135  REAL a( lda, * ), b( ldb, * )
136 * ..
137 *
138 * =====================================================================
139 *
140 * .. Parameters ..
141  REAL one
142  parameter ( one = 1.0e+0 )
143 * ..
144 * .. Local Scalars ..
145  LOGICAL notran
146 * ..
147 * .. External Functions ..
148  LOGICAL lsame
149  EXTERNAL lsame
150 * ..
151 * .. External Subroutines ..
152  EXTERNAL slaswp, strsm, xerbla
153 * ..
154 * .. Intrinsic Functions ..
155  INTRINSIC max
156 * ..
157 * .. Executable Statements ..
158 *
159 * Test the input parameters.
160 *
161  info = 0
162  notran = lsame( trans, 'N' )
163  IF( .NOT.notran .AND. .NOT.lsame( trans, 'T' ) .AND. .NOT.
164  \$ lsame( trans, 'C' ) ) THEN
165  info = -1
166  ELSE IF( n.LT.0 ) THEN
167  info = -2
168  ELSE IF( nrhs.LT.0 ) THEN
169  info = -3
170  ELSE IF( lda.LT.max( 1, n ) ) THEN
171  info = -5
172  ELSE IF( ldb.LT.max( 1, n ) ) THEN
173  info = -8
174  END IF
175  IF( info.NE.0 ) THEN
176  CALL xerbla( 'SGETRS', -info )
177  RETURN
178  END IF
179 *
180 * Quick return if possible
181 *
182  IF( n.EQ.0 .OR. nrhs.EQ.0 )
183  \$ RETURN
184 *
185  IF( notran ) THEN
186 *
187 * Solve A * X = B.
188 *
189 * Apply row interchanges to the right hand sides.
190 *
191  CALL slaswp( nrhs, b, ldb, 1, n, ipiv, 1 )
192 *
193 * Solve L*X = B, overwriting B with X.
194 *
195  CALL strsm( 'Left', 'Lower', 'No transpose', 'Unit', n, nrhs,
196  \$ one, a, lda, b, ldb )
197 *
198 * Solve U*X = B, overwriting B with X.
199 *
200  CALL strsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n,
201  \$ nrhs, one, a, lda, b, ldb )
202  ELSE
203 *
204 * Solve A**T * X = B.
205 *
206 * Solve U**T *X = B, overwriting B with X.
207 *
208  CALL strsm( 'Left', 'Upper', 'Transpose', 'Non-unit', n, nrhs,
209  \$ one, a, lda, b, ldb )
210 *
211 * Solve L**T *X = B, overwriting B with X.
212 *
213  CALL strsm( 'Left', 'Lower', 'Transpose', 'Unit', n, nrhs, one,
214  \$ a, lda, b, ldb )
215 *
216 * Apply row interchanges to the solution vectors.
217 *
218  CALL slaswp( nrhs, b, ldb, 1, n, ipiv, -1 )
219  END IF
220 *
221  RETURN
222 *
223 * End of SGETRS
224 *
subroutine strsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
STRSM
Definition: strsm.f:183
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine slaswp(N, A, LDA, K1, K2, IPIV, INCX)
SLASWP performs a series of row interchanges on a general rectangular matrix.
Definition: slaswp.f:116
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55

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