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

1.1     ! bertrand    1:       SUBROUTINE DPTTRS( 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: *  DPTTRS solves a tridiagonal system of the form
        !            19: *     A * X = B
        !            20: *  using the L*D*L' factorization of A computed by DPTTRF.  D is a
        !            21: *  diagonal matrix specified in the vector D, L is a unit bidiagonal
        !            22: *  matrix whose subdiagonal is specified in the vector E, and X and B
        !            23: *  are N by NRHS matrices.
        !            24: *
        !            25: *  Arguments
        !            26: *  =========
        !            27: *
        !            28: *  N       (input) INTEGER
        !            29: *          The order of the tridiagonal 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) DOUBLE PRECISION array, dimension (N)
        !            36: *          The n diagonal elements of the diagonal matrix D from the
        !            37: *          L*D*L' factorization of A.
        !            38: *
        !            39: *  E       (input) DOUBLE PRECISION array, dimension (N-1)
        !            40: *          The (n-1) subdiagonal elements of the unit bidiagonal factor
        !            41: *          L from the L*D*L' factorization of A.  E can also be regarded
        !            42: *          as the superdiagonal of the unit bidiagonal factor U from the
        !            43: *          factorization A = U'*D*U.
        !            44: *
        !            45: *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
        !            46: *          On entry, the right hand side vectors B for the system of
        !            47: *          linear equations.
        !            48: *          On exit, the solution vectors, X.
        !            49: *
        !            50: *  LDB     (input) INTEGER
        !            51: *          The leading dimension of the array B.  LDB >= max(1,N).
        !            52: *
        !            53: *  INFO    (output) INTEGER
        !            54: *          = 0: successful exit
        !            55: *          < 0: if INFO = -k, the k-th argument had an illegal value
        !            56: *
        !            57: *  =====================================================================
        !            58: *
        !            59: *     .. Local Scalars ..
        !            60:       INTEGER            J, JB, NB
        !            61: *     ..
        !            62: *     .. External Functions ..
        !            63:       INTEGER            ILAENV
        !            64:       EXTERNAL           ILAENV
        !            65: *     ..
        !            66: *     .. External Subroutines ..
        !            67:       EXTERNAL           DPTTS2, XERBLA
        !            68: *     ..
        !            69: *     .. Intrinsic Functions ..
        !            70:       INTRINSIC          MAX, MIN
        !            71: *     ..
        !            72: *     .. Executable Statements ..
        !            73: *
        !            74: *     Test the input arguments.
        !            75: *
        !            76:       INFO = 0
        !            77:       IF( N.LT.0 ) THEN
        !            78:          INFO = -1
        !            79:       ELSE IF( NRHS.LT.0 ) THEN
        !            80:          INFO = -2
        !            81:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
        !            82:          INFO = -6
        !            83:       END IF
        !            84:       IF( INFO.NE.0 ) THEN
        !            85:          CALL XERBLA( 'DPTTRS', -INFO )
        !            86:          RETURN
        !            87:       END IF
        !            88: *
        !            89: *     Quick return if possible
        !            90: *
        !            91:       IF( N.EQ.0 .OR. NRHS.EQ.0 )
        !            92:      $   RETURN
        !            93: *
        !            94: *     Determine the number of right-hand sides to solve at a time.
        !            95: *
        !            96:       IF( NRHS.EQ.1 ) THEN
        !            97:          NB = 1
        !            98:       ELSE
        !            99:          NB = MAX( 1, ILAENV( 1, 'DPTTRS', ' ', N, NRHS, -1, -1 ) )
        !           100:       END IF
        !           101: *
        !           102:       IF( NB.GE.NRHS ) THEN
        !           103:          CALL DPTTS2( N, NRHS, D, E, B, LDB )
        !           104:       ELSE
        !           105:          DO 10 J = 1, NRHS, NB
        !           106:             JB = MIN( NRHS-J+1, NB )
        !           107:             CALL DPTTS2( N, JB, D, E, B( 1, J ), LDB )
        !           108:    10    CONTINUE
        !           109:       END IF
        !           110: *
        !           111:       RETURN
        !           112: *
        !           113: *     End of DPTTRS
        !           114: *
        !           115:       END