sandbox/bugs/mgbc.c

Box-boundary values are not set consistently

Here the quadtree version is demonstrated. The bottom-left ghost cell has a value of s = 5, However, on a multigrid (or Cartesian grid) it becomes s = 1. I wish it was 3?

set xr [-0.3:0.6]
set yr [-0.3:0.6]
set size square
set key off
plot 'log' w l lw 2, 'out' u 1:2:3 w labels

//#include "grid/multigrid.h" // <- uncomment for MG

scalar s[];

s[left]   = dirichlet (2.);
s[bottom] = dirichlet (2.);

int main() {
  init_grid (4);
  foreach()
    s[] = 1.;
  output_cells (stderr);
  foreach()
    foreach_neighbor(1)
      printf ("%g %g %g\n", x, y, s[]);
}