NAG Library Routine Document

f06bcf (dcsg)

1
Purpose

f06bcf reconstructs the parameters c and s of a real plane rotation from the tangent of that rotation.

2
Specification

Fortran Interface
Subroutine f06bcf ( t, c, s)
Real (Kind=nag_wp), Intent (In):: t
Real (Kind=nag_wp), Intent (Out):: c, s
C Header Interface
#include <nagmk26.h>
void  f06bcf_ (const double *t, double *c, double *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 c0 and s has the same sign as t.
If t<ε, where ε is the machine precision, the routine sets c=1 and s=t; if t>1/ε, the routine sets c= 1t  and s=signt.

4
References

None.

5
Arguments

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.

6
Error Indicators and Warnings

None.

7
Accuracy

Not applicable.

8
Parallelism and Performance

f06bcf is not threaded in any implementation.

9
Further Comments

None.

10
Example

None.