Minimum viable refinement example?

[iljah]

Given

#define AMREX_SPACEDIM 3
#include "AMReX_Geometry.H"
#include "AMReX_MultiFab.H"
#include "AMReX_RealBox.H"
int main(int argc, char* argv[]) {
	using amrex::IntVect;
	amrex::Initialize(argc, argv); {
	amrex::Box domain{IntVect{0, 0, 0}, IntVect{1, 1, 1}};
	amrex::BoxArray ba;
	ba.define(domain); ba.maxSize(2147483647);
	amrex::Geometry geom; geom.define(
		domain, amrex::RealBox({0, 0, 0}, {1, 1, 1}),
		amrex::CoordSys::cartesian, amrex::Array<int, 3>{1, 1, 1});
	amrex::DistributionMapping dm{ba};
	amrex::MultiFab grid{ba, dm, 1, 0};
	} amrex::Finalize();
	return 0;
}

how do I refine the cell at i=j=k=1? AMR example of Basics.html doesn't mention any function(s) related to AMR.

As I undestand it, after refinement I'd have two separate "grids" where one is the original above and the other is 2x2x2 cell grid with smaller cells.
Do I need to already have several Boxes and/or BoxArrays and/or Geometries and/or DistributionMappings and/or MultiFabs before refining or will I get new ones from refining function(s)?

https://amrex-codes.github.io/amrex/doxygen/namespaceamrex.html has 9 versions of refine function but I'm not sure which ones I should call nor in what order, or whether they're even what I'm after.

[iljah]

Related question #4220

[iljah]

Based on #4907 cell at i=j=k=1 can be "refined" as:

amrex::Box domain2{IntVect{2, 2, 2}, IntVect{3, 3, 3}};

and data transferred to it using InterpFromCoarseLevel

[ankithadas]

I know this doesn't answer your specific question directly, but I would highly recommend that you have a look at this repository https://github.com/AMReX-Codes/amrex-tutorials

Regarding

Based on #4907 cell at i=j=k=1 can be "refined" as:

amrex::Box domain2{IntVect{2, 2, 2}, IntVect{3, 3, 3}};

and data transferred to it using InterpFromCoarseLevel

This operation does not really refine a region. All you have done is define a new Box with the bounds provided. Box does not hold any array data, only the index bounds.

Refining typically involves identifying the specific cells to be refined (tagging), creating a new BoxArray that encompasses those cells, and allocating memory and creating a new MultiFab that maps to the refined region. This explanation provides a basic overview, although several steps have been omitted for brevity.