PHYS_Remarks:

1. The LEOS equation of state toggle selects between gamma-law equations of state (LEOS = 1) and whatever a user may wish to implement as an alternative (LEOS > 1). The isothermal case (gamma = 1) requires that LEOS = 1 and XISO be set to .TRUE., as the isothermal case is treated as a special case in the code.
   
   
2. The existence of both the XHYDRO and XFORCE switches is primarily a debugging tool, but a useful one. Setting XHYDRO to .TRUE. and XFORCE to .FALSE. reduces the calculation to one of pure advection. The converse case is not physically meaningful. Setting both of these switches to .FALSE., however, allows calculations of radiation transport through static media to be performed with a minimum of CPU cost.
   
   
3. If XTOTNRG is set to .TRUE., then the ZEUS-MP field array, "e(i,j,k)" is used to store the total gas energy rather than the internal energy. This option is not valid if radiation, gravity, or magnetic fields are present.
   
   
4. The gravity switches are designed around the following logic:
   • XGRAV and XGRVFFT are "top-level" switches that decide whether gravity -- by any means other than a point-mass potential -- is computed at all. XGRVFFT is reserved for 3D cartesian grids with triply-periodic problems. For other general potential problems (2D or 3D), set XGRAV to .TRUE. and XGRVFFT to .FALSE.
   • A GM/r potential may be used in 1D or 2D by setting XGRAV and XSPHGRV to .TRUE.
   • The point-mass potential is treated is as a special case. If a point-mass potential is desired, set XPTMASS to .TRUE. and XGRAV, XGRVFFT, and XSPHGRV to .FALSE.
   
   
5. The moving grid has only been fully implemented for parallel execution for the case of grid motion along the 1-axis.