LAPACK  3.10.0
LAPACK: Linear Algebra PACKage

◆ dpotrs()

subroutine dpotrs ( character  UPLO,
integer  N,
integer  NRHS,
double precision, dimension( lda, * )  A,
integer  LDA,
double precision, dimension( ldb, * )  B,
integer  LDB,
integer  INFO 
)

DPOTRS

Download DPOTRS + dependencies [TGZ] [ZIP] [TXT]

Purpose:
 DPOTRS 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 DPOTRF.
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 DOUBLE PRECISION 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 DPOTRF.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,N).
[in,out]B
          B is DOUBLE PRECISION 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.

Definition at line 109 of file dpotrs.f.

110 *
111 * -- LAPACK computational routine --
112 * -- LAPACK is a software package provided by Univ. of Tennessee, --
113 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
114 *
115 * .. Scalar Arguments ..
116  CHARACTER UPLO
117  INTEGER INFO, LDA, LDB, N, NRHS
118 * ..
119 * .. Array Arguments ..
120  DOUBLE PRECISION A( LDA, * ), B( LDB, * )
121 * ..
122 *
123 * =====================================================================
124 *
125 * .. Parameters ..
126  DOUBLE PRECISION ONE
127  parameter( one = 1.0d+0 )
128 * ..
129 * .. Local Scalars ..
130  LOGICAL UPPER
131 * ..
132 * .. External Functions ..
133  LOGICAL LSAME
134  EXTERNAL lsame
135 * ..
136 * .. External Subroutines ..
137  EXTERNAL dtrsm, xerbla
138 * ..
139 * .. Intrinsic Functions ..
140  INTRINSIC max
141 * ..
142 * .. Executable Statements ..
143 *
144 * Test the input parameters.
145 *
146  info = 0
147  upper = lsame( uplo, 'U' )
148  IF( .NOT.upper .AND. .NOT.lsame( uplo, 'L' ) ) THEN
149  info = -1
150  ELSE IF( n.LT.0 ) THEN
151  info = -2
152  ELSE IF( nrhs.LT.0 ) THEN
153  info = -3
154  ELSE IF( lda.LT.max( 1, n ) ) THEN
155  info = -5
156  ELSE IF( ldb.LT.max( 1, n ) ) THEN
157  info = -7
158  END IF
159  IF( info.NE.0 ) THEN
160  CALL xerbla( 'DPOTRS', -info )
161  RETURN
162  END IF
163 *
164 * Quick return if possible
165 *
166  IF( n.EQ.0 .OR. nrhs.EQ.0 )
167  $ RETURN
168 *
169  IF( upper ) THEN
170 *
171 * Solve A*X = B where A = U**T *U.
172 *
173 * Solve U**T *X = B, overwriting B with X.
174 *
175  CALL dtrsm( 'Left', 'Upper', 'Transpose', 'Non-unit', n, nrhs,
176  $ one, a, lda, b, ldb )
177 *
178 * Solve U*X = B, overwriting B with X.
179 *
180  CALL dtrsm( 'Left', 'Upper', 'No transpose', 'Non-unit', n,
181  $ nrhs, one, a, lda, b, ldb )
182  ELSE
183 *
184 * Solve A*X = B where A = L*L**T.
185 *
186 * Solve L*X = B, overwriting B with X.
187 *
188  CALL dtrsm( 'Left', 'Lower', 'No transpose', 'Non-unit', n,
189  $ nrhs, one, a, lda, b, ldb )
190 *
191 * Solve L**T *X = B, overwriting B with X.
192 *
193  CALL dtrsm( 'Left', 'Lower', 'Transpose', 'Non-unit', n, nrhs,
194  $ one, a, lda, b, ldb )
195  END IF
196 *
197  RETURN
198 *
199 * End of DPOTRS
200 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:60
logical function lsame(CA, CB)
LSAME
Definition: lsame.f:53
subroutine dtrsm(SIDE, UPLO, TRANSA, DIAG, M, N, ALPHA, A, LDA, B, LDB)
DTRSM
Definition: dtrsm.f:181
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