get density average after copying particles and hydro density to gravity density array
get density average after copying particles and hydro density to gravity density array

evaneschneider/cholla,cholla-hydro/cholla,cholla-hydro/cholla,evaneschneider/cholla,cholla-hydro/cholla,evaneschneider/cholla,evaneschneider/cholla,cholla-hydro/cholla