NAG FL Interface
f06bef (drotj)

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1 Purpose

f06bef generates a real Jacobi plane rotation.

2 Specification

Fortran Interface
Subroutine f06bef ( job, x, y, z, c, s)
Real (Kind=nag_wp), Intent (Inout) :: x, y, z
Real (Kind=nag_wp), Intent (Out) :: c, s
Character (1), Intent (In) :: job
C Header Interface
#include <nag.h>
void  f06bef_ (const char *job, double *x, double *y, double *z, double *c, double *s, const Charlen length_job)
The routine may be called by the names f06bef or nagf_blas_drotj.

3 Description

f06bef generates a real Jacobi plane rotation with parameters c and s, which diagonalizes a given 2×2 real symmetric matrix:
( c s -s c ) ( x y y z ) ( c -s s c )=( a 0 0 b ) .  

4 References

None.

5 Arguments

1: job Character(1) Input
On entry: specifies the property which determines the precise form of the rotation.
job='B'
c1/2.
job='S'
0c1/2.
job='M'
|a||b|.
Constraint: job='B', 'S' or 'M'.
2: x Real (Kind=nag_wp) Input/Output
On entry: the value x, the (1,1) element of the input matrix.
On exit: the value a.
3: y Real (Kind=nag_wp) Input/Output
On entry: the value y, the (1,2) or (2,1) element of the input matrix.
On exit: the value t, the tangent of the rotation.
4: z Real (Kind=nag_wp) Input/Output
On entry: the value z. the (2,2) element of the input matrix.
On exit: the value b.
5: c Real (Kind=nag_wp) Output
On exit: the value c, the cosine of the rotation.
6: s Real (Kind=nag_wp) Output
On exit: the value s, the sine of the rotation.

6 Error Indicators and Warnings

None.

7 Accuracy

Not applicable.

8 Parallelism and Performance

f06bef is not threaded in any implementation.

9 Further Comments

None.

10 Example

None.