# NAG Library Routine Document

## 1Purpose

f06cdf reconstructs the parameters $c$ (complex) and $s$ (real) of a complex plane rotation from the tangent of that rotation.

## 2Specification

Fortran Interface
 Subroutine f06cdf ( t, c, s)
 Real (Kind=nag_wp), Intent (Out) :: s Complex (Kind=nag_wp), Intent (In) :: t Complex (Kind=nag_wp), Intent (Out) :: c
#include nagmk26.h
 void f06cdf_ ( const Complex *t, Complex *c, double *s)

## 3Description

f06cdf reconstructs the parameters $c$ (complex) and $s$ (real) of a complex plane rotation, from the value of the tangent $t$, as returned by f06cbf:
 $c=signRett t⁢1+t2 , s=ct.$
If $\left|t\right|<\sqrt{\epsilon }$, where $\epsilon$ is the machine precision, the routine sets:
 $c=signRettt, s=signRett.$

None.

## 5Arguments

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

None.

Not applicable.

## 8Parallelism and Performance

f06cdf is not threaded in any implementation.