SRC/dla_gbamv.f(3)

NAME
SRC/dla_gbamv.f

SYNOPSIS

  Functions/Subroutines
subroutine dla_gbamv (trans, m, n, kl, ku, alpha, ab, ldab, x, incx, beta, y, incy)
DLA_GBAMV performs a matrix-vector operation to calculate error bounds.

Function/Subroutine Documentation

  subroutine dla_gbamv (integer trans, integer m, integer n, integer kl, integer ku, double precision alpha, double precision, dimension( ldab, * ) ab, integer ldab, double precision, dimension( * ) x, integer incx, double precision beta, double precision, dimension( * ) y, integer incy)

DLA_GBAMV performs a matrix-vector operation to calculate error bounds.

Purpose:

    !>
    !> DLA_GBAMV  performs one of the matrix-vector operations
    !>
    !>         y := alpha*abs(A)*abs(x) + beta*abs(y),
    !>    or   y := alpha*abs(A)**T*abs(x) + beta*abs(y),
    !>
    !> where alpha and beta are scalars, x and y are vectors and A is an
    !> m by n matrix.
    !>
    !> This function is primarily used in calculating error bounds.
    !> To protect against underflow during evaluation, components in
    !> the resulting vector are perturbed away from zero by (N+1)
    !> times the underflow threshold.  To prevent unnecessarily large
    !> errors for block-structure embedded in general matrices,
    !>  zero components are not perturbed.  A zero
    !> entry is considered  if all multiplications involved
    !> in computing that entry have at least one zero multiplicand.
    !>

Parameters
    TRANS

    !>          TRANS is INTEGER
    !>           On entry, TRANS specifies the operation to be performed as
    !>           follows:
    !>
    !>             BLAS_NO_TRANS      y := alpha*abs(A)*abs(x) + beta*abs(y)
    !>             BLAS_TRANS         y := alpha*abs(A**T)*abs(x) + beta*abs(y)
    !>             BLAS_CONJ_TRANS    y := alpha*abs(A**T)*abs(x) + beta*abs(y)
    !>
    !>           Unchanged on exit.
    !>

    M

    !>          M is INTEGER
    !>           On entry, M specifies the number of rows of the matrix A.
    !>           M must be at least zero.
    !>           Unchanged on exit.
    !>

    N

    !>          N is INTEGER
    !>           On entry, N specifies the number of columns of the matrix A.
    !>           N must be at least zero.
    !>           Unchanged on exit.
    !>

    KL

    !>          KL is INTEGER
    !>           The number of subdiagonals within the band of A.  KL >= 0.
    !>

    KU

    !>          KU is INTEGER
    !>           The number of superdiagonals within the band of A.  KU >= 0.
    !>

    ALPHA

    !>          ALPHA is DOUBLE PRECISION
    !>           On entry, ALPHA specifies the scalar alpha.
    !>           Unchanged on exit.
    !>

    AB

    !>          AB is DOUBLE PRECISION array, dimension ( LDAB, n )
    !>           Before entry, the leading m by n part of the array AB must
    !>           contain the matrix of coefficients.
    !>           Unchanged on exit.
    !>

    LDAB

    !>          LDAB is INTEGER
    !>           On entry, LDA specifies the first dimension of AB as declared
    !>           in the calling (sub) program. LDAB must be at least
    !>           max( 1, m ).
    !>           Unchanged on exit.
    !>

    X

    !>          X is DOUBLE PRECISION array, dimension
    !>           ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n'
    !>           and at least
    !>           ( 1 + ( m - 1 )*abs( INCX ) ) otherwise.
    !>           Before entry, the incremented array X must contain the
    !>           vector x.
    !>           Unchanged on exit.
    !>

    INCX

    !>          INCX is INTEGER
    !>           On entry, INCX specifies the increment for the elements of
    !>           X. INCX must not be zero.
    !>           Unchanged on exit.
    !>

    BETA

    !>          BETA is DOUBLE PRECISION
    !>           On entry, BETA specifies the scalar beta. When BETA is
    !>           supplied as zero then Y need not be set on input.
    !>           Unchanged on exit.
    !>

    Y

    !>          Y is DOUBLE PRECISION array, dimension
    !>           ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n'
    !>           and at least
    !>           ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.
    !>           Before entry with BETA non-zero, the incremented array Y
    !>           must contain the vector y. On exit, Y is overwritten by the
    !>           updated vector y.
    !>           If either m or n is zero, then Y not referenced and the function
    !>           performs a quick return.
    !>

    INCY

    !>          INCY is INTEGER
    !>           On entry, INCY specifies the increment for the elements of
    !>           Y. INCY must not be zero.
    !>           Unchanged on exit.
    !>
    !>  Level 2 Blas routine.
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 185 of file dla_gbamv.f.

Author

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