coments and warings

Author: WeiqunZhang

Src/Amr/AMReX_AmrLevel.H

@@ -952,6 +952,15 @@ void AmrLevel::RK (int order, int state_type, Real time, Real dt, int iteration,
     }
 }
 
+// Store coarse AMR level RK stage data into the FillPatcher on the next
+// finer level.  The fine level will use this data during RK substeps to
+// fill its ghost cells at the coarse/fine boundary (via FillRKPatch →
+// FillPatcher::fillRK).
+//
+// A fresh FillPatcher is always constructed here — not built lazily like
+// FillPatcherFill does — because this function is the *only* place the
+// FillPatcher for the next finer level is created.  It is destroyed later
+// in post_timestep/resetFillPatcher after the fine level catches up.
 template <std::size_t order>
 void AmrLevel::storeRKCoarseData (int state_type, Real time, Real dt,
                                   MultiFab const& S_old,

Src/F_Interfaces/Base/AMReX_rungekutta_fi.cpp

@@ -52,7 +52,7 @@ extern "C"
             [=] (Array<MultiFab,3> const& rkk)
             {
                 if (store) {
-                    std::array<MultiFab const*,3> rkp{{&rkk[0], &rkk[1], &rkk[2]}};
+                    std::array<MultiFab const*,3> rkp{{rkk.data(), &rkk[1], &rkk[2]}};
                     store(ctx, old_state, rkp.data());
                 }
             },
@@ -81,7 +81,7 @@ extern "C"
             [=] (Array<MultiFab,4> const& rkk)
             {
                 if (store) {
-                    std::array<MultiFab const*,4> rkp{{&rkk[0], &rkk[1], &rkk[2], &rkk[3]}};
+                    std::array<MultiFab const*,4> rkp{{rkk.data(), &rkk[1], &rkk[2], &rkk[3]}};
                     store(ctx, old_state, rkp.data());
                 }
             },

Tests/FortranInterface/Advection_F_RK/Source/fillpatch_mod.F90

@@ -90,6 +90,14 @@ subroutine fillpatch_stage (lev, time, phi, rk_order, stage, iteration, ncycle)
     end if
   end subroutine fillpatch_stage
 
+  ! Store coarse AMR level RK stage data into the FillPatcher on the next
+  ! finer level so that the fine level can fill its ghost cells at the
+  ! coarse/fine boundary during RK substeps (via fillpatch_stage -> fill_rk).
+  !
+  ! build_fillpatcher (not ensure_fillpatcher) is called here because this is
+  ! the only place the FillPatcher for lev+1 is created. It is not built
+  ! anywhere during fine-level advance; we must build it now. The FillPatcher
+  ! is destroyed later by reset_fillpatcher after the fine level catches up.
   subroutine store_rk3_fillpatcher (lev, time, dt, s_old, rk, nghost)
     use amr_data_module, only : fillpatcher
     integer, intent(in) :: lev, nghost