DLA_GBAMV(1LAPACK routine (version 3.2)DLA_GBAMV(1)NAME
DLA_GBAMV - performs one of the matrix-vector operations y :=
alpha*abs(A)*abs(x) + beta*abs(y),
SYNOPSIS
SUBROUTINE DLA_GBAMV( TRANS, M, N, KL, KU, ALPHA, AB, LDAB, X, INCX,
BETA, Y, INCY )
IMPLICIT NONE
DOUBLE PRECISION ALPHA, BETA
INTEGER INCX, INCY, LDAB, M, N, KL, KU, TRANS
DOUBLE PRECISION AB( LDAB, * ), X( * ), Y( * )
PURPOSE
DLA_GEAMV performs one of the matrix-vector operations
or y := alpha*abs(A)'*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 pro‐
tect 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,
"symbolically" zero components are not perturbed. A zero entry is con‐
sidered "symbolic" if all multiplications involved in computing that
entry have at least one zero multiplicand.
ARGUMENTS
TRANS - INTEGER
On entry, TRANS specifies the operation to be performed as fol‐
lows:
BLAS_NO_TRANS y := alpha*abs(A)*abs(x) + beta*abs(y)
BLAS_TRANS y := alpha*abs(A')*abs(x) +
beta*abs(y)
BLAS_CONJ_TRANS y := alpha*abs(A')*abs(x) +
beta*abs(y) Unchanged on exit.
M - INTEGER
On entry, M specifies the number of rows of the matrix A. M
must be at least zero. Unchanged on exit.
N - INTEGER
On entry, N specifies the number of columns of the matrix A. N
must be at least zero. Unchanged on exit.
KL - INTEGER
The number of subdiagonals within the band of A. KL >= 0.
KU - INTEGER
The number of superdiagonals within the band of A. KU >= 0.
ALPHA - DOUBLE PRECISION
On entry, ALPHA specifies the scalar alpha. Unchanged on exit.
A - DOUBLE PRECISION array of DIMENSION ( LDA, n )
Before entry, the leading m by n part of the array A must con‐
tain the matrix of coefficients. Unchanged on exit.
LDA - INTEGER
On entry, LDA specifies the first dimension of A as declared in
the calling (sub) program. LDA must be at least max( 1, m ).
Unchanged on exit.
X - DOUBLE PRECISION array of DIMENSION at least
( 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 - INTEGER
On entry, INCX specifies the increment for the elements of X.
INCX must not be zero. Unchanged on exit.
BETA - 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 - DOUBLE PRECISION array of DIMENSION at least
( 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.
INCY - INTEGER
On entry, INCY specifies the increment for the elements of Y.
INCY must not be zero. Unchanged on exit. Level 2 Blas rou‐
tine.
LAPACK routine (version 3.2) November 2008 DLA_GBAMV(1)