Defect in XSH atan2

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        Defect report from : Loic Domaigne , personal interest

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@ page 0 line 0 section atan2 comment {atan2}

Problem:

Edition of Specification (Year): 2003

Defect code :  2. Omission

Missing example.

Action:

Converting Cartesian to Polar coordinates system 

The function below uses atan2() to convert a 2d vector expressed in
cartesian coordinates to the polar coordinates. 


#include <math.h>

typedef struct
{
  double x;
  double y;
} cartesian2d_t ;

typedef struct 
{
  double rho;
  double theta;
} polar_t;

polar_t 
cartesian_to_polar(const cartesian2d_t v /* vector in cartesian */
                   )
{
  polar_t polar_v;  /* v in polar */

  polar_v.rho   = sqrt (v.x*v.x + v.y*v.y);
  polar_v.theta = atan2 (v.y, v.x);

  return polar_v;
}


Note1: There are alternative ways to compute the angle theta, using 
e.g. asin(), acos() or atan(). However, atan2() presents here two 
advantages:
    - the angle's quadrant is automatically determined. 
    - the singular case v.x==0 is taken into account.

Note2: similar examples might be derived using atan2f(), atan2l().