## Developer Reference

• 2020.2
• 07/15/2020
• Public Content
Contents

# ?la_gbamv

Performs a matrix-vector operation to calculate error bounds.

## Syntax

Include Files
• mkl.fi
Description
The
?la_gbamv
function performs one of the matrix-vector operations defined as
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,
A
is an
m
-by-
n
matrix, with
kl
sub-diagonals and
ku
super-diagonals.
This function is primarily used in calculating error bounds. To protect against underflow during evaluation, the function perturbs components in the resulting vector away from zero by
(
n
+ 1)
times the underflow threshold. To prevent unnecessarily large errors for block structure embedded in general matrices, the function does not perturb
symbolically
zero components. A zero entry is considered
symbolic
if all multiplications involved in computing that entry have at least one zero multiplicand.
Input Parameters
trans
INTEGER
. Specifies the operation to be performed:
If
trans
= 'BLAS_NO_TRANS'
, then
y
:=
alpha
*abs(
A
)*abs(
x
) +
beta
*abs(
y
)
If
trans
= 'BLAS_TRANS'
, then
y
:=
alpha
*abs(
A
T
)*abs(
x
) +
beta
*abs(
y
)
If
trans
= 'BLAS_CONJ_TRANS'
, then
y
:=
alpha
*abs(
A
T
)*abs(
x
) +
beta
*abs(
y
)
The parameter is unchanged on exit.
m
INTEGER
. Specifies the number of rows of the matrix
A
.
The value of
m
must be at least zero. Unchanged on exit.
n
INTEGER
. Specifies the number of columns of the matrix
A
.
The value of
n
must be at least zero. Unchanged on exit.
kl
INTEGER
. Specifies the number of sub-diagonals within the band of
A
.
kl
0.
ku
INTEGER
. Specifies the number of super-diagonals within the band of
A
.
ku
0.
alpha
REAL
for
sla_gbamv
and
cla_gbamv
DOUBLE PRECISION
for
dla_gbamv
and
zla_gbamv
Specifies the scalar
alpha