F06BEF (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F06BEF

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

+ Contents

    1  Purpose
    7  Accuracy
    9  Example

1  Purpose

F06BEF generates a real Jacobi plane rotation.

2  Specification

SUBROUTINE F06BEF ( JOB, X, Y, Z, C, S)
REAL (KIND=nag_wp)  X, Y, Z, C, S
CHARACTER(1)  JOB

3  Description

F06BEF generates a real Jacobi plane rotation with parameters c and s, which diagonalizes a given 2 by 2 real symmetric matrix:
c s -s c x y y z c -s s c = a 0 0 b .

4  References

None.

5  Parameters

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'
ab.
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  Further Comments

None.

9  Example

None.

F06BEF (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012