NAME:
  hptodiam
 PURPOSE:   (one line only)
  Compute diameter of an asteroid given H$_V$ and V-band geometric albedo
 DESCRIPTION:
 CATEGORY:
  Astronomy
 CALLING SEQUENCE:
  d = hptodiam(hv,pv)
 INPUTS:
  hv - V-band absolute magnitude
  pv - V-band geometric albedo
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  return value is the diameter of the asteroid in kilometers
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2014/05/19