# NAG Library Routine Document

## 1Purpose

f06ccf reconstructs the parameters $c$ (real) and $s$ (complex) of a complex plane rotation from the tangent of that rotation.

## 2Specification

Fortran Interface
 Subroutine f06ccf ( t, c, s)
 Real (Kind=nag_wp), Intent (Out) :: c Complex (Kind=nag_wp), Intent (In) :: t Complex (Kind=nag_wp), Intent (Out) :: s
#include nagmk26.h
 void f06ccf_ (const Complex *t, double *c, Complex *s)

## 3Description

f06ccf reconstructs the parameters $c$ (real) and $s$ (complex) of a complex plane rotation, from the value of the tangent $t$, as returned by f06caf:
 $c=11+t2 , s=ct,$
so that $c$ is always real and non-negative.
If $\left|t\right|<\sqrt{\epsilon }$, where $\epsilon$ is the machine precision, the routine sets $c=1$ and $s=t$.

None.

## 5Arguments

1:     $\mathbf{t}$ – Complex (Kind=nag_wp)Input
On entry: the value $t$, the tangent of the rotation.
2:     $\mathbf{c}$ – Real (Kind=nag_wp)Output
On exit: the value $c$, the cosine of the rotation.
3:     $\mathbf{s}$ – Complex (Kind=nag_wp)Output
On exit: the value $s$, the sine of the rotation.

None.

Not applicable.

## 8Parallelism and Performance

f06ccf is not threaded in any implementation.

None.

## 10Example

None.
© The Numerical Algorithms Group Ltd, Oxford, UK. 2017