LAPACK  3.8.0
LAPACK: Linear Algebra PACKage

◆ spotrs()

subroutine spotrs ( character  UPLO,
integer  N,
integer  NRHS,
real, dimension( lda, * )  A,
integer  LDA,
real, dimension( ldb, * )  B,
integer  LDB,
integer  INFO 
)

SPOTRS

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Purpose:
 SPOTRS solves a system of linear equations A*X = B with a symmetric
 positive definite matrix A using the Cholesky factorization
 A = U**T*U or A = L*L**T computed by SPOTRF.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
          = 'U':  Upper triangle of A is stored;
          = 'L':  Lower triangle of A is stored.
[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 triangular factor U or L from the Cholesky factorization
          A = U**T*U or A = L*L**T, as computed by SPOTRF.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[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
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
December 2016

Definition at line 112 of file spotrs.f.

112 *
113 * -- LAPACK computational routine (version 3.7.0) --
114 * -- LAPACK is a software package provided by Univ. of Tennessee, --
115 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
116 * December 2016
117 *
118 * .. Scalar Arguments ..
119  CHARACTER uplo
120  INTEGER info, lda, ldb, n, nrhs
121 * ..
122 * .. Array Arguments ..
123  REAL a( lda, * ), b( ldb, * )
124 * ..
125 *
126 * =====================================================================
127 *
128 * .. Parameters ..
129  REAL one
130  parameter( one = 1.0e+0 )
131 * ..
132 * .. Local Scalars ..
133  LOGICAL upper
134 * ..
135 * .. External Functions ..
136  LOGICAL lsame
137  EXTERNAL lsame
138 * ..
139 * .. External Subroutines ..
140  EXTERNAL strsm, xerbla
141 * ..
142 * .. Intrinsic Functions ..
143  INTRINSIC max
144 * ..
145 * .. Executable Statements ..
146 *
147 * Test the input parameters.
148 *
149  info = 0
150  upper = lsame( uplo, 'U' )
151  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
152  info = -1
153  ELSE IF( n.LT.0 ) THEN
154  info = -2
155  ELSE IF( nrhs.LT.0 ) THEN
156  info = -3
157  ELSE IF( lda.LT.max( 1, n ) ) THEN
158  info = -5
159  ELSE IF( ldb.LT.max( 1, n ) ) THEN
160  info = -7
161  END IF
162  IF( info.NE.0 ) THEN
163  CALL xerbla( 'SPOTRS', -info )
164  RETURN
165  END IF
166 *
167 * Quick return if possible
168 *
169  IF( n.EQ.0 .OR. nrhs.EQ.0 )
170  $ RETURN
171 *
172  IF( upper ) THEN
173 *
174 * Solve A*X = B where A = U**T *U.
175 *
176 * Solve U**T *X = B, overwriting B with X.
177 *
178  CALL strsm( 'Left', 'Upper', 'Transpose', 'Non-unit', n, nrhs,
179  $ one, a, lda, b, ldb )
180 *
181 * Solve U*X = B, overwriting B with X.
182 *
183  CALL strsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n,
184  $ nrhs, one, a, lda, b, ldb )
185  ELSE
186 *
187 * Solve A*X = B where A = L*L**T.
188 *
189 * Solve L*X = B, overwriting B with X.
190 *
191  CALL strsm( 'Left', 'Lower', 'No transpose', 'Non-unit', n,
192  $ nrhs, one, a, lda, b, ldb )
193 *
194 * Solve L**T *X = B, overwriting B with X.
195 *
196  CALL strsm( 'Left', 'Lower', 'Transpose', 'Non-unit', n, nrhs,
197  $ one, a, lda, b, ldb )
198  END IF
199 *
200  RETURN
201 *
202 * End of SPOTRS
203 *
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
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:55
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