palPa palPa - HA, Dec to Parallactic Angle

Description:
Converts HA, Dec to Parallactic Angle.

Invocation:
double palPa( double ha, double dec, double phi );

Arguments:

ha = double (Given)
Hour angle in radians (Geocentric apparent)
dec = double (Given)
Declination in radians (Geocentric apparent)
phi = double (Given)
Observatory latitude in radians (geodetic)

Returned Value:

palPa = double
Parallactic angle in the range -pi to $+$pi.

Notes: