NAG Library Routine Document

F06BHF

+− Contents

1 Purpose

9 Example

F06BHF applies a real similarity rotation to a

2

2

real symmetric matrix.

SUBROUTINE F06BHF (

X, Y, Z, C, S)

REAL (KIND=nag_wp)

X, Y, Z, C, S

F06BHF applies a real similarity rotation, with parameters

c

and

s

, to a given

2

2

real symmetric matrix; that is, it performs the operation:

(\begin{matrix} x & y \\ y & z \end{matrix}) \leftarrow (\begin{array}{rc} c & s \\ - s & c \end{array}) (\begin{matrix} x & y \\ y & z \end{matrix}) (\begin{array}{cr} c & - s \\ s & c \end{array}) .

None.

1: X – REAL (KIND=nag_wp)Input/Output: On entry: the value $x$ , the $(1, 1)$ element of the input matrix.

On exit: the transformed value $x$ .
2: 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 transformed value $y$ .
3: Z – REAL (KIND=nag_wp)Input/Output: On entry: the value $z$ , the $(2, 2)$ element of the input matrix.

On exit: the transformed value $z$ .
4: C – REAL (KIND=nag_wp)Input: On entry: the value $c$ , the cosine of the rotation.
5: S – REAL (KIND=nag_wp)Input: On entry: the value $s$ , the sine of the rotation.