Procedure

   SpiceDouble twopi_c ( void ) 

Abstract

 
   Return twice the value of pi (the ratio of the circumference of 
   a circle to its diameter). 
 

Required_Reading

 
   None. 
 

Keywords

 
   CONSTANTS 
 

Brief_I/O

 
   The function returns twice the value of pi. 
 

Detailed_Input

 
   None. 
 

Detailed_Output

 
   The function returns twice the value of pi (the ratio of 
   a circle's circumference to its diameter), determined by 
   the ACOS function. That is, 
 
           twopi = acos ( -1. ) * 2. 
 

Parameters

 
   None. 
 

Exceptions

 
   Error free. 
 

Files

 
   None. 
 

Particulars

 
   The first time the function is referenced, the value is computed 
   as shown above. The value is saved, and returned directly upon 
   subsequent reference. 
 

Examples

 
   The code fragment below illustrates the use of twopi_c. 
 
        /. 
               The longitude of the ascending node is the angle 
               between the x-axis and the node vector, n. 
                                                       - 
        ./
               node = acos ( n[0] / vnorm_c( n ) );
 
               if ( node < 0.D0 )
                  {
                  node = node + twopi_c();
                  }

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

   W.L. Taber      (JPL) 
   I.M. Underwood  (JPL) 
   E.D. Wright     (JPL)
 

Version

   -CSPICE Version 1.0.0, 08-FEB-1998 (EDW)

Index_Entries

 
   twice the value of pi 
 

Link to routine twopi_c source file twopi_c.c