Question about mask techniques in the IAMR codes

[ruohai0925]

Hello all,

When I learned the mask codes, I realized it is a kind of technique to differentiate different boundary conditions (fine-fine, coarse-fine, physical). According to different mask values, we know the different boundary conditions. Then, from my guessing, we can re-fill the ghost cell values according to the different boundary condition. The advantage is we can use the unified FORTRAN subroutines to do the operations (e.g. compRHS & updatevel ) without considering the differences between different boundary conditions. I mean, the FORTRAN subroutines in the AMReX and IAMR do not include the information about CPU and boundary conditions. It seems like an "encapsulation".

I am not sure if I understand it right or not. If it is like this, can someone direct some codes fractions (operations) for me to learn the mask technique better?

[ruohai0925]

Here is an example to illustrate more about the above understanding. In the lid_driven case, u top=1, originally the ghost cell values for u lie on the boundary (see this question: AMReX-Codes/amrex#258 ), I guess it uses masks to signal it, then change the ghost cell values in the C++ subroutines to cell centered, so that in the FORTRAN subroutine, we can use the unified form to calculate the RHS (standard finite difference)