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

1.1     ! bertrand    1:       SUBROUTINE ZPTTRS( UPLO, 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:       CHARACTER          UPLO
        !            10:       INTEGER            INFO, LDB, N, NRHS
        !            11: *     ..
        !            12: *     .. Array Arguments ..
        !            13:       DOUBLE PRECISION   D( * )
        !            14:       COMPLEX*16         B( LDB, * ), E( * )
        !            15: *     ..
        !            16: *
        !            17: *  Purpose
        !            18: *  =======
        !            19: *
        !            20: *  ZPTTRS solves a tridiagonal system of the form
        !            21: *     A * X = B
        !            22: *  using the factorization A = U'*D*U or A = L*D*L' computed by ZPTTRF.
        !            23: *  D is a diagonal matrix specified in the vector D, U (or L) is a unit
        !            24: *  bidiagonal matrix whose superdiagonal (subdiagonal) is specified in
        !            25: *  the vector E, and X and B are N by NRHS matrices.
        !            26: *
        !            27: *  Arguments
        !            28: *  =========
        !            29: *
        !            30: *  UPLO    (input) CHARACTER*1
        !            31: *          Specifies the form of the factorization and whether the
        !            32: *          vector E is the superdiagonal of the upper bidiagonal factor
        !            33: *          U or the subdiagonal of the lower bidiagonal factor L.
        !            34: *          = 'U':  A = U'*D*U, E is the superdiagonal of U
        !            35: *          = 'L':  A = L*D*L', E is the subdiagonal of L
        !            36: *
        !            37: *  N       (input) INTEGER
        !            38: *          The order of the tridiagonal matrix A.  N >= 0.
        !            39: *
        !            40: *  NRHS    (input) INTEGER
        !            41: *          The number of right hand sides, i.e., the number of columns
        !            42: *          of the matrix B.  NRHS >= 0.
        !            43: *
        !            44: *  D       (input) DOUBLE PRECISION array, dimension (N)
        !            45: *          The n diagonal elements of the diagonal matrix D from the
        !            46: *          factorization A = U'*D*U or A = L*D*L'.
        !            47: *
        !            48: *  E       (input) COMPLEX*16 array, dimension (N-1)
        !            49: *          If UPLO = 'U', the (n-1) superdiagonal elements of the unit
        !            50: *          bidiagonal factor U from the factorization A = U'*D*U.
        !            51: *          If UPLO = 'L', the (n-1) subdiagonal elements of the unit
        !            52: *          bidiagonal factor L from the factorization A = L*D*L'.
        !            53: *
        !            54: *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
        !            55: *          On entry, the right hand side vectors B for the system of
        !            56: *          linear equations.
        !            57: *          On exit, the solution vectors, X.
        !            58: *
        !            59: *  LDB     (input) INTEGER
        !            60: *          The leading dimension of the array B.  LDB >= max(1,N).
        !            61: *
        !            62: *  INFO    (output) INTEGER
        !            63: *          = 0: successful exit
        !            64: *          < 0: if INFO = -k, the k-th argument had an illegal value
        !            65: *
        !            66: *  =====================================================================
        !            67: *
        !            68: *     .. Local Scalars ..
        !            69:       LOGICAL            UPPER
        !            70:       INTEGER            IUPLO, J, JB, NB
        !            71: *     ..
        !            72: *     .. External Functions ..
        !            73:       INTEGER            ILAENV
        !            74:       EXTERNAL           ILAENV
        !            75: *     ..
        !            76: *     .. External Subroutines ..
        !            77:       EXTERNAL           XERBLA, ZPTTS2
        !            78: *     ..
        !            79: *     .. Intrinsic Functions ..
        !            80:       INTRINSIC          MAX, MIN
        !            81: *     ..
        !            82: *     .. Executable Statements ..
        !            83: *
        !            84: *     Test the input arguments.
        !            85: *
        !            86:       INFO = 0
        !            87:       UPPER = ( UPLO.EQ.'U' .OR. UPLO.EQ.'u' )
        !            88:       IF( .NOT.UPPER .AND. .NOT.( UPLO.EQ.'L' .OR. UPLO.EQ.'l' ) ) THEN
        !            89:          INFO = -1
        !            90:       ELSE IF( N.LT.0 ) THEN
        !            91:          INFO = -2
        !            92:       ELSE IF( NRHS.LT.0 ) THEN
        !            93:          INFO = -3
        !            94:       ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
        !            95:          INFO = -7
        !            96:       END IF
        !            97:       IF( INFO.NE.0 ) THEN
        !            98:          CALL XERBLA( 'ZPTTRS', -INFO )
        !            99:          RETURN
        !           100:       END IF
        !           101: *
        !           102: *     Quick return if possible
        !           103: *
        !           104:       IF( N.EQ.0 .OR. NRHS.EQ.0 )
        !           105:      $   RETURN
        !           106: *
        !           107: *     Determine the number of right-hand sides to solve at a time.
        !           108: *
        !           109:       IF( NRHS.EQ.1 ) THEN
        !           110:          NB = 1
        !           111:       ELSE
        !           112:          NB = MAX( 1, ILAENV( 1, 'ZPTTRS', UPLO, N, NRHS, -1, -1 ) )
        !           113:       END IF
        !           114: *
        !           115: *     Decode UPLO
        !           116: *
        !           117:       IF( UPPER ) THEN
        !           118:          IUPLO = 1
        !           119:       ELSE
        !           120:          IUPLO = 0
        !           121:       END IF
        !           122: *
        !           123:       IF( NB.GE.NRHS ) THEN
        !           124:          CALL ZPTTS2( IUPLO, N, NRHS, D, E, B, LDB )
        !           125:       ELSE
        !           126:          DO 10 J = 1, NRHS, NB
        !           127:             JB = MIN( NRHS-J+1, NB )
        !           128:             CALL ZPTTS2( IUPLO, N, JB, D, E, B( 1, J ), LDB )
        !           129:    10    CONTINUE
        !           130:       END IF
        !           131: *
        !           132:       RETURN
        !           133: *
        !           134: *     End of ZPTTRS
        !           135: *
        !           136:       END