nag_dwaxpby (f16ehc) (PDF version)
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nag_dwaxpby (f16ehc)
▸
▿
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
1
Purpose
nag_dwaxpby (f16ehc)
computes the sum of two scaled vectors, preserving input, for real scalars and vectors.
2
Specification
#include <nag.h>
#include <nagf16.h>
void
nag_dwaxpby (
Integer
n
,
double
alpha
,
const double
x
[],
Integer
incx
,
double
beta
,
const double
y
[],
Integer
incy
,
double
w
[],
Integer
incw
,
NagError *
fail
)
3
Description
nag_dwaxpby (f16ehc)
performs the operation
w
←
α
x
+
β
y
,
where
x
and
y
are
n
-element real vectors, and
α
and
β
are real scalars.
4
References
Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001)
Basic Linear Algebra Subprograms Technical (BLAST) Forum Standard
University of Tennessee, Knoxville, Tennessee
http://www.netlib.org/blas/blast-forum/blas-report.pdf
5
Arguments
1:
n
–
Integer
Input
On entry
:
n
, the number of elements in
x
,
y
and
w
.
Constraint
:
n
≥
0
.
2:
alpha
–
double
Input
On entry
: the scalar
α
.
3:
x
[
dim
]
–
const double
Input
Note:
the dimension,
dim
, of the array
x
must be at least
max
1
,
1
+
n
-
1
×
incx
.
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
n
=
0
,
x
is not referenced and may be
NULL
.
4:
incx
–
Integer
Input
On entry
: the increment in the subscripts of
x
between successive elements of
x
.
Constraint
:
incx
≠
0
.
5:
beta
–
double
Input
On entry
: the scalar
β
.
6:
y
[
dim
]
–
const double
Input
Note:
the dimension,
dim
, of the array
y
must be at least
max
1
,
1
+
n
-
1
×
incy
.
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
β
=
0.0
or
n
=
0
,
y
is not referenced and may be
NULL
.
7:
incy
–
Integer
Input
On entry
: the increment in the subscripts of
y
between successive elements of
y
.
Constraint
:
incy
≠
0
.
8:
w
[
dim
]
–
double
Input/Output
Note:
the dimension,
dim
, of the array
w
must be at least
max
1
,
1
+
n
-
1
×
incw
.
On entry
: if
incw
≠
1
, intermediate elements of
w
may contain values and will not be referenced; the other elements will be overwritten and need not be set.
On exit
: the elements
w
i
of the vector
w
will be stored in
w
as follows.
If
incw
>
0
,
w
i
is in
w
[
i
-
1
×
incw
]
, for
i
=
1
,
2
,
…
,
n
.
If
incw
<
0
,
w
i
is in
w
[
n
-
i
×
incw
]
, for
i
=
1
,
2
,
…
,
n
.
Intermediate elements of
w
are not referenced.
9:
incw
–
Integer
Input
On entry
: the increment in the subscripts of
w
between successive elements of
w
.
Constraint
:
incw
≠
0
.
10:
fail
–
NagError *
Input/Output
The NAG error argument (see
Section 3.7
in How to Use the NAG Library and its Documentation).
6
Error Indicators and Warnings
NE_ALLOC_FAIL
Dynamic memory allocation failed.
See
Section 2.3.1.2
in How to Use the NAG Library and its Documentation for further information.
NE_BAD_PARAM
On entry, argument
value
had an illegal value.
NE_INT
On entry,
incw
=
value
.
Constraint:
incw
≠
0
.
On entry,
incx
=
value
.
Constraint:
incx
≠
0
.
On entry,
incy
=
value
.
Constraint:
incy
≠
0
.
On entry,
n
=
value
.
Constraint:
n
≥
0
.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See
Section 2.7.5
in How to Use the NAG Library and its Documentation for further information.
7
Accuracy
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
nag_dwaxpby (f16ehc)
is not threaded in any implementation.
9
Further Comments
None.
10
Example
This example computes the result of a scaled vector accumulation for
α
=
3
,
x
=
-
6
,
4.5
,
3.7
,
2.1
,
-
4
T
,
β
=
-
1
,
y
=
-
5.1
,
-
5
,
6.4
,
-
2.4
,
-
3
T
.
x
and
y
, and also the sum vector
w
, are stored in reverse order.
10.1
Program Text
Program Text (f16ehce.c)
10.2
Program Data
Program Data (f16ehce.d)
10.3
Program Results
Program Results (f16ehce.r)
nag_dwaxpby (f16ehc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG Library Manual
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017