Real computeSum(const Vector< LevelData< FArrayBox > * > &a_phi, const Vector< int > &a_nRefFine, const Vector< CoordSys< FArrayBox, FluxBox > * > &a_coordSysPtr, const Interval &a_comps=Interval(0, 0), const int &a_lBase=0)
Returns the volume-weighted sum (integral) of phi over all valid regions.