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Annotation of rpl/lapack/lapack/dptsv.f, revision 1.1

1.1     ! bertrand    1:       SUBROUTINE DPTSV( N, NRHS, D, E, B, LDB, INFO )
        !             2: *
        !             3: *  -- LAPACK routine (version 3.2) --
        !             4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
        !             5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
        !             6: *     November 2006
        !             7: *
        !             8: *     .. Scalar Arguments ..
        !             9:       INTEGER            INFO, LDB, N, NRHS
        !            10: *     ..
        !            11: *     .. Array Arguments ..
        !            12:       DOUBLE PRECISION   B( LDB, * ), D( * ), E( * )
        !            13: *     ..
        !            14: *
        !            15: *  Purpose
        !            16: *  =======
        !            17: *
        !            18: *  DPTSV computes the solution to a real system of linear equations
        !            19: *  A*X = B, where A is an N-by-N symmetric positive definite tridiagonal
        !            20: *  matrix, and X and B are N-by-NRHS matrices.
        !            21: *
        !            22: *  A is factored as A = L*D*L**T, and the factored form of A is then
        !            23: *  used to solve the system of equations.
        !            24: *
        !            25: *  Arguments
        !            26: *  =========
        !            27: *
        !            28: *  N       (input) INTEGER
        !            29: *          The order of the matrix A.  N >= 0.
        !            30: *
        !            31: *  NRHS    (input) INTEGER
        !            32: *          The number of right hand sides, i.e., the number of columns
        !            33: *          of the matrix B.  NRHS >= 0.
        !            34: *
        !            35: *  D       (input/output) DOUBLE PRECISION array, dimension (N)
        !            36: *          On entry, the n diagonal elements of the tridiagonal matrix
        !            37: *          A.  On exit, the n diagonal elements of the diagonal matrix
        !            38: *          D from the factorization A = L*D*L**T.
        !            39: *
        !            40: *  E       (input/output) DOUBLE PRECISION array, dimension (N-1)
        !            41: *          On entry, the (n-1) subdiagonal elements of the tridiagonal
        !            42: *          matrix A.  On exit, the (n-1) subdiagonal elements of the
        !            43: *          unit bidiagonal factor L from the L*D*L**T factorization of
        !            44: *          A.  (E can also be regarded as the superdiagonal of the unit
        !            45: *          bidiagonal factor U from the U**T*D*U factorization of A.)
        !            46: *
        !            47: *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
        !            48: *          On entry, the N-by-NRHS right hand side matrix B.
        !            49: *          On exit, if INFO = 0, the N-by-NRHS solution matrix X.
        !            50: *
        !            51: *  LDB     (input) INTEGER
        !            52: *          The leading dimension of the array B.  LDB >= max(1,N).
        !            53: *
        !            54: *  INFO    (output) INTEGER
        !            55: *          = 0:  successful exit
        !            56: *          < 0:  if INFO = -i, the i-th argument had an illegal value
        !            57: *          > 0:  if INFO = i, the leading minor of order i is not
        !            58: *                positive definite, and the solution has not been
        !            59: *                computed.  The factorization has not been completed
        !            60: *                unless i = N.
        !            61: *
        !            62: *  =====================================================================
        !            63: *
        !            64: *     .. External Subroutines ..
        !            65:       EXTERNAL           DPTTRF, DPTTRS, XERBLA
        !            66: *     ..
        !            67: *     .. Intrinsic Functions ..
        !            68:       INTRINSIC          MAX
        !            69: *     ..
        !            70: *     .. Executable Statements ..
        !            71: *
        !            72: *     Test the input parameters.
        !            73: *
        !            74:       INFO = 0
        !            75:       IF( N.LT.0 ) THEN
        !            76:          INFO = -1
        !            77:       ELSE IF( NRHS.LT.0 ) THEN
        !            78:          INFO = -2
        !            79:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
        !            80:          INFO = -6
        !            81:       END IF
        !            82:       IF( INFO.NE.0 ) THEN
        !            83:          CALL XERBLA( 'DPTSV ', -INFO )
        !            84:          RETURN
        !            85:       END IF
        !            86: *
        !            87: *     Compute the L*D*L' (or U'*D*U) factorization of A.
        !            88: *
        !            89:       CALL DPTTRF( N, D, E, INFO )
        !            90:       IF( INFO.EQ.0 ) THEN
        !            91: *
        !            92: *        Solve the system A*X = B, overwriting B with X.
        !            93: *
        !            94:          CALL DPTTRS( N, NRHS, D, E, B, LDB, INFO )
        !            95:       END IF
        !            96:       RETURN
        !            97: *
        !            98: *     End of DPTSV
        !            99: *
        !           100:       END