f06bpf (PDF version)
F06 (blas) Chapter Contents
F06 (blas) Chapter Introduction
NAG Library Manual
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NAG Library Routine Document
f06bpf (deig2)
▸
▿
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
1
Purpose
f06bpf
returns an eigenvalue of a
2
by
2
real symmetric matrix.
2
Specification
Fortran Interface
Function f06bpf (
a
,
b
,
c
)
Real (Kind=nag_wp)
::
f06bpf
Real (Kind=nag_wp), Intent (In)
::
a
,
b
,
c
C Header Interface
#include nagmk26.h
double
f06bpf_ (
const double *
a
,
const double *
b
,
const double *
c
)
3
Description
f06bpf
returns an eigenvalue of the
2
by
2
real symmetric matrix
a
b
b
c
,
via the function name. The result is intended for use as a shift in symmetric eigenvalue routines.
The eigenvalue is computed as
c
-
b
f
+
sign
f
×
1
+
f
2
,
where
f
=
a
-
c
2
b
.
This is the eigenvalue nearer to
c
if
a
≠
c
, and is equal to
c
-
b
if
a
=
c
.
4
References
None.
5
Arguments
1:
a
– Real (Kind=nag_wp)
Input
On entry
: the value
a
, the
1
,
1
element of the input matrix.
2:
b
– Real (Kind=nag_wp)
Input
On entry
: the value
b
, the
1
,
2
or
2
,
1
element of the input matrix.
3:
c
– Real (Kind=nag_wp)
Input
On entry
: the value
c
, the
2
,
2
element of the input matrix.
6
Error Indicators and Warnings
None.
7
Accuracy
Not applicable.
8
Parallelism and Performance
f06bpf
is not threaded in any implementation.
9
Further Comments
None.
10
Example
None.
f06bpf (PDF version)
F06 (blas) Chapter Contents
F06 (blas) Chapter Introduction
NAG Library Manual
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017