FLASH4.6.2 API

   Compute the values of integral quantities (eg. total energy)
   and write them to an ASCII file.  If this is the initial step,
   create the file and write a header to it before writing the data.

   Presently, this supports 1, 2, and 3-d Cartesian geometry and 2-d
   cylindrical geometry (r,z).  More geometries can be added by
   modifying the volume of each zone (dvol).

   Users should modify this routine if they want to store any
   quantities other than default values in the flash.dat.  Make sure
   to modify the nGlobalSum parameter to match the number of
   quantities written.  Also make sure to modify the header to match
   the names of quantities with those calculated in the lsum and
   gsum arrays.