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Annotation of rpl/lapack/lapack/dptsv.f, revision 1.9

1.9     ! bertrand    1: *> \brief \b DPTSV
        !             2: *
        !             3: *  =========== DOCUMENTATION ===========
        !             4: *
        !             5: * Online html documentation available at 
        !             6: *            http://www.netlib.org/lapack/explore-html/ 
        !             7: *
        !             8: *> \htmlonly
        !             9: *> Download DPTSV + dependencies 
        !            10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dptsv.f"> 
        !            11: *> [TGZ]</a> 
        !            12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dptsv.f"> 
        !            13: *> [ZIP]</a> 
        !            14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dptsv.f"> 
        !            15: *> [TXT]</a>
        !            16: *> \endhtmlonly 
        !            17: *
        !            18: *  Definition:
        !            19: *  ===========
        !            20: *
        !            21: *       SUBROUTINE DPTSV( N, NRHS, D, E, B, LDB, INFO )
        !            22: * 
        !            23: *       .. Scalar Arguments ..
        !            24: *       INTEGER            INFO, LDB, N, NRHS
        !            25: *       ..
        !            26: *       .. Array Arguments ..
        !            27: *       DOUBLE PRECISION   B( LDB, * ), D( * ), E( * )
        !            28: *       ..
        !            29: *  
        !            30: *
        !            31: *> \par Purpose:
        !            32: *  =============
        !            33: *>
        !            34: *> \verbatim
        !            35: *>
        !            36: *> DPTSV computes the solution to a real system of linear equations
        !            37: *> A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
        !            38: *> matrix, and X and B are N-by-NRHS matrices.
        !            39: *>
        !            40: *> A is factored as A = L*D*L**T, and the factored form of A is then
        !            41: *> used to solve the system of equations.
        !            42: *> \endverbatim
        !            43: *
        !            44: *  Arguments:
        !            45: *  ==========
        !            46: *
        !            47: *> \param[in] N
        !            48: *> \verbatim
        !            49: *>          N is INTEGER
        !            50: *>          The order of the matrix A.  N >= 0.
        !            51: *> \endverbatim
        !            52: *>
        !            53: *> \param[in] NRHS
        !            54: *> \verbatim
        !            55: *>          NRHS is INTEGER
        !            56: *>          The number of right hand sides, i.e., the number of columns
        !            57: *>          of the matrix B.  NRHS >= 0.
        !            58: *> \endverbatim
        !            59: *>
        !            60: *> \param[in,out] D
        !            61: *> \verbatim
        !            62: *>          D is DOUBLE PRECISION array, dimension (N)
        !            63: *>          On entry, the n diagonal elements of the tridiagonal matrix
        !            64: *>          A.  On exit, the n diagonal elements of the diagonal matrix
        !            65: *>          D from the factorization A = L*D*L**T.
        !            66: *> \endverbatim
        !            67: *>
        !            68: *> \param[in,out] E
        !            69: *> \verbatim
        !            70: *>          E is DOUBLE PRECISION array, dimension (N-1)
        !            71: *>          On entry, the (n-1) subdiagonal elements of the tridiagonal
        !            72: *>          matrix A.  On exit, the (n-1) subdiagonal elements of the
        !            73: *>          unit bidiagonal factor L from the L*D*L**T factorization of
        !            74: *>          A.  (E can also be regarded as the superdiagonal of the unit
        !            75: *>          bidiagonal factor U from the U**T*D*U factorization of A.)
        !            76: *> \endverbatim
        !            77: *>
        !            78: *> \param[in,out] B
        !            79: *> \verbatim
        !            80: *>          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
        !            81: *>          On entry, the N-by-NRHS right hand side matrix B.
        !            82: *>          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
        !            83: *> \endverbatim
        !            84: *>
        !            85: *> \param[in] LDB
        !            86: *> \verbatim
        !            87: *>          LDB is INTEGER
        !            88: *>          The leading dimension of the array B.  LDB >= max(1,N).
        !            89: *> \endverbatim
        !            90: *>
        !            91: *> \param[out] INFO
        !            92: *> \verbatim
        !            93: *>          INFO is INTEGER
        !            94: *>          = 0:  successful exit
        !            95: *>          < 0:  if INFO = -i, the i-th argument had an illegal value
        !            96: *>          > 0:  if INFO = i, the leading minor of order i is not
        !            97: *>                positive definite, and the solution has not been
        !            98: *>                computed.  The factorization has not been completed
        !            99: *>                unless i = N.
        !           100: *> \endverbatim
        !           101: *
        !           102: *  Authors:
        !           103: *  ========
        !           104: *
        !           105: *> \author Univ. of Tennessee 
        !           106: *> \author Univ. of California Berkeley 
        !           107: *> \author Univ. of Colorado Denver 
        !           108: *> \author NAG Ltd. 
        !           109: *
        !           110: *> \date November 2011
        !           111: *
        !           112: *> \ingroup doubleOTHERcomputational
        !           113: *
        !           114: *  =====================================================================
1.1       bertrand  115:       SUBROUTINE DPTSV( N, NRHS, D, E, B, LDB, INFO )
                    116: *
1.9     ! bertrand  117: *  -- LAPACK computational routine (version 3.4.0) --
1.1       bertrand  118: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                    119: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
1.9     ! bertrand  120: *     November 2011
1.1       bertrand  121: *
                    122: *     .. Scalar Arguments ..
                    123:       INTEGER            INFO, LDB, N, NRHS
                    124: *     ..
                    125: *     .. Array Arguments ..
                    126:       DOUBLE PRECISION   B( LDB, * ), D( * ), E( * )
                    127: *     ..
                    128: *
                    129: *  =====================================================================
                    130: *
                    131: *     .. External Subroutines ..
                    132:       EXTERNAL           DPTTRF, DPTTRS, XERBLA
                    133: *     ..
                    134: *     .. Intrinsic Functions ..
                    135:       INTRINSIC          MAX
                    136: *     ..
                    137: *     .. Executable Statements ..
                    138: *
                    139: *     Test the input parameters.
                    140: *
                    141:       INFO = 0
                    142:       IF( N.LT.0 ) THEN
                    143:          INFO = -1
                    144:       ELSE IF( NRHS.LT.0 ) THEN
                    145:          INFO = -2
                    146:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
                    147:          INFO = -6
                    148:       END IF
                    149:       IF( INFO.NE.0 ) THEN
                    150:          CALL XERBLA( 'DPTSV ', -INFO )
                    151:          RETURN
                    152:       END IF
                    153: *
1.8       bertrand  154: *     Compute the L*D*L**T (or U**T*D*U) factorization of A.
1.1       bertrand  155: *
                    156:       CALL DPTTRF( N, D, E, INFO )
                    157:       IF( INFO.EQ.0 ) THEN
                    158: *
                    159: *        Solve the system A*X = B, overwriting B with X.
                    160: *
                    161:          CALL DPTTRS( N, NRHS, D, E, B, LDB, INFO )
                    162:       END IF
                    163:       RETURN
                    164: *
                    165: *     End of DPTSV
                    166: *
                    167:       END