LAPACK  3.4.1
LAPACK: Linear Algebra PACKage
dpotrs.f
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00001 *> \brief \b DPOTRS
00002 *
00003 *  =========== DOCUMENTATION ===========
00004 *
00005 * Online html documentation available at 
00006 *            http://www.netlib.org/lapack/explore-html/ 
00007 *
00008 *> \htmlonly
00009 *> Download DPOTRS + dependencies 
00010 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dpotrs.f"> 
00011 *> [TGZ]</a> 
00012 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dpotrs.f"> 
00013 *> [ZIP]</a> 
00014 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dpotrs.f"> 
00015 *> [TXT]</a>
00016 *> \endhtmlonly 
00017 *
00018 *  Definition:
00019 *  ===========
00020 *
00021 *       SUBROUTINE DPOTRS( UPLO, N, NRHS, A, LDA, B, LDB, INFO )
00022 * 
00023 *       .. Scalar Arguments ..
00024 *       CHARACTER          UPLO
00025 *       INTEGER            INFO, LDA, LDB, N, NRHS
00026 *       ..
00027 *       .. Array Arguments ..
00028 *       DOUBLE PRECISION   A( LDA, * ), B( LDB, * )
00029 *       ..
00030 *  
00031 *
00032 *> \par Purpose:
00033 *  =============
00034 *>
00035 *> \verbatim
00036 *>
00037 *> DPOTRS solves a system of linear equations A*X = B with a symmetric
00038 *> positive definite matrix A using the Cholesky factorization
00039 *> A = U**T*U or A = L*L**T computed by DPOTRF.
00040 *> \endverbatim
00041 *
00042 *  Arguments:
00043 *  ==========
00044 *
00045 *> \param[in] UPLO
00046 *> \verbatim
00047 *>          UPLO is CHARACTER*1
00048 *>          = 'U':  Upper triangle of A is stored;
00049 *>          = 'L':  Lower triangle of A is stored.
00050 *> \endverbatim
00051 *>
00052 *> \param[in] N
00053 *> \verbatim
00054 *>          N is INTEGER
00055 *>          The order of the matrix A.  N >= 0.
00056 *> \endverbatim
00057 *>
00058 *> \param[in] NRHS
00059 *> \verbatim
00060 *>          NRHS is INTEGER
00061 *>          The number of right hand sides, i.e., the number of columns
00062 *>          of the matrix B.  NRHS >= 0.
00063 *> \endverbatim
00064 *>
00065 *> \param[in] A
00066 *> \verbatim
00067 *>          A is DOUBLE PRECISION array, dimension (LDA,N)
00068 *>          The triangular factor U or L from the Cholesky factorization
00069 *>          A = U**T*U or A = L*L**T, as computed by DPOTRF.
00070 *> \endverbatim
00071 *>
00072 *> \param[in] LDA
00073 *> \verbatim
00074 *>          LDA is INTEGER
00075 *>          The leading dimension of the array A.  LDA >= max(1,N).
00076 *> \endverbatim
00077 *>
00078 *> \param[in,out] B
00079 *> \verbatim
00080 *>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
00081 *>          On entry, the right hand side matrix B.
00082 *>          On exit, the solution matrix X.
00083 *> \endverbatim
00084 *>
00085 *> \param[in] LDB
00086 *> \verbatim
00087 *>          LDB is INTEGER
00088 *>          The leading dimension of the array B.  LDB >= max(1,N).
00089 *> \endverbatim
00090 *>
00091 *> \param[out] INFO
00092 *> \verbatim
00093 *>          INFO is INTEGER
00094 *>          = 0:  successful exit
00095 *>          < 0:  if INFO = -i, the i-th argument had an illegal value
00096 *> \endverbatim
00097 *
00098 *  Authors:
00099 *  ========
00100 *
00101 *> \author Univ. of Tennessee 
00102 *> \author Univ. of California Berkeley 
00103 *> \author Univ. of Colorado Denver 
00104 *> \author NAG Ltd. 
00105 *
00106 *> \date November 2011
00107 *
00108 *> \ingroup doublePOcomputational
00109 *
00110 *  =====================================================================
00111       SUBROUTINE DPOTRS( UPLO, N, NRHS, A, LDA, B, LDB, INFO )
00112 *
00113 *  -- LAPACK computational routine (version 3.4.0) --
00114 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00115 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00116 *     November 2011
00117 *
00118 *     .. Scalar Arguments ..
00119       CHARACTER          UPLO
00120       INTEGER            INFO, LDA, LDB, N, NRHS
00121 *     ..
00122 *     .. Array Arguments ..
00123       DOUBLE PRECISION   A( LDA, * ), B( LDB, * )
00124 *     ..
00125 *
00126 *  =====================================================================
00127 *
00128 *     .. Parameters ..
00129       DOUBLE PRECISION   ONE
00130       PARAMETER          ( ONE = 1.0D+0 )
00131 *     ..
00132 *     .. Local Scalars ..
00133       LOGICAL            UPPER
00134 *     ..
00135 *     .. External Functions ..
00136       LOGICAL            LSAME
00137       EXTERNAL           LSAME
00138 *     ..
00139 *     .. External Subroutines ..
00140       EXTERNAL           DTRSM, XERBLA
00141 *     ..
00142 *     .. Intrinsic Functions ..
00143       INTRINSIC          MAX
00144 *     ..
00145 *     .. Executable Statements ..
00146 *
00147 *     Test the input parameters.
00148 *
00149       INFO = 0
00150       UPPER = LSAME( UPLO, 'U' )
00151       IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN
00152          INFO = -1
00153       ELSE IF( N.LT.0 ) THEN
00154          INFO = -2
00155       ELSE IF( NRHS.LT.0 ) THEN
00156          INFO = -3
00157       ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
00158          INFO = -5
00159       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
00160          INFO = -7
00161       END IF
00162       IF( INFO.NE.0 ) THEN
00163          CALL XERBLA( 'DPOTRS', -INFO )
00164          RETURN
00165       END IF
00166 *
00167 *     Quick return if possible
00168 *
00169       IF( N.EQ.0 .OR. NRHS.EQ.0 )
00170      $   RETURN
00171 *
00172       IF( UPPER ) THEN
00173 *
00174 *        Solve A*X = B where A = U**T *U.
00175 *
00176 *        Solve U**T *X = B, overwriting B with X.
00177 *
00178          CALL DTRSM( 'Left', 'Upper', 'Transpose', 'Non-unit', N, NRHS,
00179      $               ONE, A, LDA, B, LDB )
00180 *
00181 *        Solve U*X = B, overwriting B with X.
00182 *
00183          CALL DTRSM( 'Left', 'Upper', 'No transpose', 'Non-unit', N,
00184      $               NRHS, ONE, A, LDA, B, LDB )
00185       ELSE
00186 *
00187 *        Solve A*X = B where A = L*L**T.
00188 *
00189 *        Solve L*X = B, overwriting B with X.
00190 *
00191          CALL DTRSM( 'Left', 'Lower', 'No transpose', 'Non-unit', N,
00192      $               NRHS, ONE, A, LDA, B, LDB )
00193 *
00194 *        Solve L**T *X = B, overwriting B with X.
00195 *
00196          CALL DTRSM( 'Left', 'Lower', 'Transpose', 'Non-unit', N, NRHS,
00197      $               ONE, A, LDA, B, LDB )
00198       END IF
00199 *
00200       RETURN
00201 *
00202 *     End of DPOTRS
00203 *
00204       END
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