NAG Library Manual, Mark 29.2
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NAG CL Interface
f16jsc (zamax_val)
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NAG Library Manual, Mark 29.2
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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
© The Numerical Algorithms Group Ltd. 2023
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1
Purpose
f16jsc
computes, with respect to absolute value, the largest component of a complex vector, along with the index of that component.
2
Specification
copy
#include <nag.h>
void
f16jsc
(
Integer
n
,
const Complex
x
[],
Integer
incx
,
Integer *
k
,
double *
r
,
NagError *
fail
)
The function may be called by the names:
f16jsc
,
nag_blast_zamax_val
or
nag_zamax_val
.
3
Description
f16jsc
computes, with respect to absolute value, the largest component,
r
, of an
n
-element complex vector
x
, and determines the smallest index,
k
, such that
r
=
|
Re
x
k
|
+
|
Im
x
k
|
=
max
j
|
Re
x
j
|
+
|
Im
x
j
|
.
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:
n
–
Integer
Input
On entry
:
n
, the number of elements in
x
.
Constraint
:
n
≥
0
.
2:
x
[
dim
]
–
const Complex
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
.
3:
incx
–
Integer
Input
On entry
: the increment in the subscripts of
x
between successive elements of
x
.
Constraint
:
incx
≠
0
.
4:
k
–
Integer *
Output
On exit
:
k
, the index, from the set
{
0
,
1
,
…
,
n
-
1
}
, of the largest component of
x
with respect to absolute value. If
n
=
0
on input then
k
is returned as
−1
.
5:
r
–
double *
Output
On exit
:
r
, the largest component of
x
with respect to absolute value. If
n
=
0
on input then
r
is returned as
0.0
.
6:
fail
–
NagError *
Input/Output
The NAG error argument (see
Section 7
in the Introduction to the NAG 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 NAG 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,
n
=
⟨
value
⟩
.
Constraint:
n
≥
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 NAG Library CL Interface 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
Background information to multithreading can be found in the
Multithreading
documentation.
f16jsc
is not threaded in any implementation.
9
Further Comments
None.
10
Example
This example computes the largest component with respect to absolute value and index of that component for the vector
x
=
(
-
4
+
2.1
i
,
3.7
+
4.5
i
,
-
6
+
1.2
i
)
T
.
10.1
Program Text
Program Text (f16jsce.c)
10.2
Program Data
Program Data (f16jsce.d)
10.3
Program Results
Program Results (f16jsce.r)
NAG Library Manual, Mark 29.2
Interfaces:
FL
CL
CPP
AD
PY
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NAG CL Interface Introduction
F16 (Blast) Chapter Contents
F16 (Blast) Chapter Introduction
f16js:
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© The Numerical Algorithms Group Ltd. 2023