f06bc: FL CL CPP AD PY MB

NAG FL Interface
f06bcf (dcsg)

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NAG Library Manual, Mark 30.2

Interfaces: FL CL CPP AD PY MB

NAG FL Interface Introduction

F06 (Blas) Chapter Contents

F06 (Blas) Chapter Introduction

f06bc: FL CL CPP AD PY MB

▸▿ Contents

1 Purpose

2 Specification

3 Description

4 References

5 Arguments

6 Error Indicators and Warnings

7 Accuracy

8 Parallelism and Performance

9 Further Comments

10 Example

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 <nag.h>

void	f06bcf_ (const double t, double c, double *s)

The routine may be called by the names f06bcf or nagf_blas_dcsg.

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 = \frac{1}{\sqrt{1 + t^{2}}}, s = c t,

so that

c \geq 0

and

s

has the same sign as

t

| t | < \sqrt{ε}

, where

ε

is the machine precision, the routine sets

c = 1

and

s = t

; if

| t | > 1 / \sqrt{ε}

, the routine sets

c = \frac{1}{| t |}

and

s = sign t

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.