# NAG FL Interfacef06bef (drotj)

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## 1Purpose

f06bef generates a real Jacobi plane rotation.

## 2Specification

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
#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.

## 3Description

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

None.

## 5Arguments

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

None.

Not applicable.