### Restriction Functions

Function: double gsl_sf_angle_restrict_symm (double theta)
Function: int gsl_sf_angle_restrict_symm_e (double * theta)
  These routines force the angle theta to lie in the range (-\pi,\pi].

Function: double gsl_sf_angle_restrict_pos (double theta)
Function: int gsl_sf_angle_restrict_pos_e (double * theta)
  These routines force the angle theta to lie in the range [0, 2\pi).