NAG Library Routine Document

a02acf (divide)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

a02acf divides one complex number, x=xr,xi, by a second complex number, y=yr,yi, returning the result in z=zr,zi.

2
Specification

Fortran Interface
Subroutine a02acf ( xr, xi, yr, yi, zr, zi)
Real (Kind=nag_wp), Intent (In):: xr, xi, yr, yi
Real (Kind=nag_wp), Intent (Out):: zr, zi
C Header Interface
#include nagmk26.h
void  a02acf_ (const double *xr, const double *xi, const double *yr, const double *yi, double *zr, double *zi)

3
Description

The result z is calculated using Smith's algorithm with scaling, from Li et al. (2002), which ensures that no unnecessary overflow or underflow occurs at intermediate stages of the computation.

4
References

Li X S, Demmel J W, Bailey D H, Henry G, Hida Y, Iskandar J, Kahan W, Kapur A, Martin M C, Tung T and Yoo D J (2002) Design, implementation and testing of extended and mixed precision BLAS ACM Trans. Math. Soft. 28(2) 152–205

5
Arguments

1:     xr – Real (Kind=nag_wp)Input
2:     xi – Real (Kind=nag_wp)Input
On entry: xr and xi, the real and imaginary parts of x, respectively.
3:     yr – Real (Kind=nag_wp)Input
4:     yi – Real (Kind=nag_wp)Input
On entry: yr and yi, the real and imaginary parts of y, respectively.
5:     zr – Real (Kind=nag_wp)Output
6:     zi – Real (Kind=nag_wp)Output
On exit: zr and zi, the real and imaginary parts of z, respectively.

6
Error Indicators and Warnings

None.

7
Accuracy

The result should be correct to machine precision.

8
Parallelism and Performance

a02acf is not threaded in any implementation.

9
Further Comments

The time taken by a02acf is negligible.
This routine must not be called with yr=0.0 and yi=0.0.

10
Example

This example finds the value of -1.7+2.6i/-3.1-0.9i.

10.1
Program Text

Program Text (a02acfe.f90)

10.2
Program Data

Program Data (a02acfe.d)

10.3
Program Results

Program Results (a02acfe.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017