NAME: 
  lcfun
 PURPOSE: 
  Compute a lightcurve function (Fourier series plus phase coefficient).
 DESCRIPTION:
  This is to be used in cases where you already know the fundamental period.
  The input independent variable is assumed to be reduced to phase of a
  fundamental period already.  The integer part of the number is not used
  by the function.
 CATEGORY:
  Mathematical
 CALLING SEQUENCE:
  lcfun,x,c,f,pder
 INPUTS:
  x - independent variable (longitude, between 0 and 360)
  c - fourier series coefficients
        0 - beta    -> linear phase coefficient
        1 - a(0)    -> constant term
        2 - a(1)    -> cos(x2pi)
        3 - b(1)    -> sin(x2pi)
        4 - a(2)    -> cos(2x2pi)
        5 - b(2)    -> sin(2x2pi)
     and so on for as many elements as in c
 OPTIONAL INPUT PARAMETERS:
  PHANG - phase angle of each observation, will be saved to common, if
             not provided will use the last values saved to common block.
             Angle is in degrees.
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  f    - Evaluated function value
  pder - (Optional) partial derivatives
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
   lc_com - one variable, phang, that is used to save the phase angle from
               one call to the next in case of calling the lcfun or lcfunf
               from a canned routine that cannot be taught to pass the
               extra independent variable.
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  94/10/10, Written by Marc W. Buie, Lowell Observatory