Procedure: thm_part_slice2d_getsun Purpose: Helper function for thm_part_slice2d. Retrieves sun vectors for all distributions within the specified time range and averages them. Input: ds: (pointer) Pointer array to particle distribution structures. trange: (double) Two element time range for the slice. Output: Returns averaged sun vector (3-vector float) on success or 0 on failure. Notes: This assumes that the spacecraft-sun vector is roughly constant over the time range of the slice. $LastChangedBy: aaflores $ $LastChangedDate: 2013-10-30 17:31:16 -0700 (Wed, 30 Oct 2013) $ $LastChangedRevision: 13454 $ $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/spdsoft/trunk/projects/themis/spacecraft/particles/slices/thm_part_slice2d_getsun.pro $