F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

# NAG Library Routine DocumentF06BCF

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.

## 1  Purpose

F06BCF reconstructs the parameters $c$ and $s$ of a real plane rotation from the tangent of that rotation.

## 2  Specification

 SUBROUTINE F06BCF ( T, C, S)
 REAL (KIND=nag_wp) T, C, S

## 3  Description

F06BCF reconstructs the parameters $c$ and $s$ of a real plane rotation from the value of the tangent $t$, as returned by F06BAF:
 $c=11+t2 , s=ct,$
so that $c\ge 0$ and $s$ has the same sign as $t$.
If $\left|t\right|<\sqrt{\epsilon }$, where $\epsilon$ is the machine precision, the routine sets $c=1$ and $s=t$; if $\left|t\right|>1/\sqrt{\epsilon }$, the routine sets $c=\frac{1}{\left|t\right|}$ and $s=\mathrm{sign}t$.

None.

## 5  Parameters

1:     T – REAL (KIND=nag_wp)Input
On entry: the value $t$, the tangent of the rotation.
2:     C – REAL (KIND=nag_wp)Output
On exit: the value $c$, the cosine of the rotation.
3:     S – REAL (KIND=nag_wp)Output
On exit: the value $s$, the sine of the rotation.

None.

Not applicable.