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twopi_c

 Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input Detailed_Output Parameters Exceptions Files Particulars Examples Restrictions Literature_References Author_and_Institution Version Index_Entries

#### Procedure

```   twopi_c ( Twice the value of pi )

SpiceDouble twopi_c ( void )

```

#### Abstract

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

```   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

```   J. Diaz del Rio     (ODC Space)
W.L. Taber          (JPL)
I.M. Underwood      (JPL)
E.D. Wright         (JPL)
```

#### Version

```   -CSPICE Version 1.0.1, 02-JUN-2021 (JDR)

Edited the header to comply with NAIF standard.

-CSPICE Version 1.0.0, 08-FEB-1998 (EDW) (WLT) (IMU)
```

#### Index_Entries

```   twice the value of pi
```
`Fri Dec 31 18:41:14 2021`