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AG CL Interface
f16eac (ddot)
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Contents
1
Purpose
2
Specification
3
Description
4
References
5
Arguments
6
Error Indicators and Warnings
7
Accuracy
8
Parallelism and Performance
9
Further Comments
▸
▿
10
Example
10.1
Program Text
10.2
Program Data
10.3
Program Results
Copyright
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AG 2024
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CL Name Style:
Short (
a00aac
)
Long (
impl_details
)
Full (
nag_info_impl_details
)
1
Purpose
f16eac
updates a scalar by a scaled dot product of two real vectors, by performing
r
←
β
r
+
α
x
T
y
.
2
Specification
copy
#include <nag.h>
void
f16eac
(
Nag_ConjType
conj
,
Integer
n
,
double
alpha
,
const double
x
[],
Integer
incx
,
double
beta
,
const double
y
[],
Integer
incy
,
double *
r
,
NagError *
fail
)
The function may be called by the names:
f16eac
,
nag_blast_ddot
or
nag_ddot
.
3
Description
f16eac
performs the operation
r
←
β
r
+
α
x
T
y
where
x
and
y
are
n
-element real vectors, and
r
,
α
and
β
real scalars. If
n
is less than zero, or, if
β
is equal to one and either
α
or
n
is equal to zero, this function returns immediately.
4
References
Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001)
Basic Linear Algebra Subprograms Technical (BLAST) Forum Standard
University of Tennessee, Knoxville, Tennessee
https://www.netlib.org/blas/blast-forum/blas-report.pdf
5
Arguments
1:
conj
–
Nag_ConjType
Input
On entry
:
conj
is not used. The presence of this argument in the BLAST standard is for consistency with the interface of the complex variant of this function.
Constraint
:
conj
=
Nag_NoConj
or
Nag_Conj
.
2:
n
–
Integer
Input
On entry
:
n
, the number of elements in
x
and
y
.
3:
alpha
–
double
Input
On entry
: the scalar
α
.
4:
x
[
1
+
(
n
-
1
)
×
|
incx
|
]
–
const double
Input
On entry
: the
n
-element vector
x
.
If
incx
>
0
,
x
i
must be stored in
x
[
(
i
-
1
)
×
incx
]
, for
i
=
1
,
2
,
…
,
n
.
If
incx
<
0
,
x
i
must be stored in
x
[
(
n
-
i
)
×
|
incx
|
]
, for
i
=
1
,
2
,
…
,
n
.
Intermediate elements of
x
are not referenced. If
α
=
0.0
or
n
=
0
,
x
is not referenced and may be
NULL
.
5:
incx
–
Integer
Input
On entry
: the increment in the subscripts of
x
between successive elements of
x
.
Constraint
:
incx
≠
0
.
6:
beta
–
double
Input
On entry
: the scalar
β
.
7:
y
[
1
+
(
n
-
1
)
×
|
incy
|
]
–
const double
Input
On entry
: the
n
-element vector
y
.
If
incy
>
0
,
y
i
must be stored in
y
[
(
i
-
1
)
×
incy
]
, for
i
=
1
,
2
,
…
,
n
.
If
incy
<
0
,
y
i
must be stored in
y
[
(
n
-
i
)
×
|
incy
|
]
, for
i
=
1
,
2
,
…
,
n
.
Intermediate elements of
y
are not referenced. If
α
=
0.0
or
n
=
0
,
y
is not referenced and may be
NULL
.
8:
incy
–
Integer
Input
On entry
: the increment in the subscripts of
y
between successive elements of
y
.
Constraint
:
incy
≠
0
.
9:
r
–
double *
Input/Output
On entry
: the initial value,
r
, to be updated. If
β
=
0.0
,
r
need not be set on entry.
On exit
: the value
r
, scaled by
β
and updated by the scaled dot product of
x
and
y
.
10:
fail
–
NagError *
Input/Output
The
N
AG error argument (see
Section 7
in the Introduction to the
N
AG Library CL Interface).
6
Error Indicators and Warnings
NE_ALLOC_FAIL
Dynamic memory allocation failed.
See
Section 3.1.2
in the Introduction to the
N
AG Library CL Interface for further information.
NE_BAD_PARAM
On entry, argument
⟨
value
⟩
had an illegal value.
NE_INT
On entry,
incx
=
⟨
value
⟩
.
Constraint:
incx
≠
0
.
On entry,
incy
=
⟨
value
⟩
.
Constraint:
incy
≠
0
.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See
Section 8
in the Introduction to the
N
AG Library CL Interface for further information.
7
Accuracy
The dot product
x
T
y
is computed using the BLAS routine DDOT.
The BLAS standard requires accurate implementations which avoid unnecessary over/underflow (see Section 2.7 of
Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001)
).
8
Parallelism and Performance
Background information to multithreading can be found in the
Multithreading
documentation.
f16eac
makes calls to BLAS and/or LAPACK routines, which may be threaded within the vendor library used by this implementation. Consult the documentation for the vendor library for further information.
Please consult the
X06 Chapter Introduction
for information on how to control and interrogate the OpenMP environment used within this function. Please also consult the
Users' Note
for your implementation for any additional implementation-specific information.
9
Further Comments
None.
10
Example
This example computes the scaled sum of two dot products,
r
=
α
1
x
T
y
+
α
2
u
T
v
, where
α
1
=
0.3
,
x
=
(
1
,
2
,
3
,
4
,
5
)
,
y
=
(
−5
,
−4
,
3
,
2
,
1
)
,
α
2
=
-
7.0
,
u
=
v
=
(
0.4
,
0.3
,
0.2
,
0.1
)
.
y
and
v
are stored in reverse order, and
u
is stored in reverse order in every other element of a real array.
10.1
Program Text
Program Text (f16eace.c)
10.2
Program Data
Program Data (f16eace.d)
10.3
Program Results
Program Results (f16eace.r)
N
AG Library Manual, Mark 30.3
Interfaces:
FL
CL
CPP
AD
PY
MB
N
AG CL Interface Introduction
F16 (Blast) Chapter Contents
F16 (Blast) Chapter Introduction
f16ea:
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CL
CPP
AD
PY
MB
Copyright
N
AG 2024