Demonstration of stencil distribution on Chapel

stencil-demo.chpl

import StencilDist.stencilDist;
import StencilDist.boundaries;

const side_low  =  1;
const side_high = -1;
config const n = 10;
config const nghost = 2;
config const periodic = false;
const Space = {1..n};
const AllSpace = Space.expand((nghost,));

const Dist = Space dmapped new stencilDist(Space, fluff=(nghost,), periodic=periodic);
var A: [Dist] real;

// Initialize interior values
sync forall i in A.domain do
  A[i] = i:real;
sync A.updateFluff();

// Print full array including ghost cells
writeln("Full array (no ghosts):");
for i in A.domain do // replace this with forall to see print order randomized
  writeln("inner: A[", i, "] = ", A[i]);

// Access and print the ghost boundaries
writeln("\nGhost boundaries (before update):");
if periodic {
    for (arr_val, edge) in A.boundaries() {
        // writeln(edge, " ", edge.type:string);
        // writeln(arr_val, " ", arr_val.type:string);
        for edge_dir in edge {
            if edge_dir==side_low {
                writeln("Left ghost: ", arr_val);
            }
            if edge_dir==side_high {
                writeln("Right ghost: ", arr_val);
            } 
        }
    }
}
else {
    for i in AllSpace {
        if !Space.contains(i) {
            if i<Space.low then
                writeln("Left ghost: ", A[i]);
            else
                writeln("Right ghost: ", A[i]);
        }
    }
}

writeln("\nUpdating...");
sync forall i in AllSpace {
    if Space.contains(i) then
       var pass = 1; // anything dummy; here keeping it unchanged
    else {
        if i<Space.low then
            A[i] = A[i+n];
        else
            A[i] = A[i%n]; // periodic
    }
}
sync A.updateFluff();

for i in AllSpace { // replace this with forall to see print order randomized
    if Space.contains(i) then
       writeln("inner: A[", i, "] = ", A[i]);
    else {
        if i<Space.low then
            writeln("left: A[", i, "] = ", A[i]);
        else
            writeln("right: A[", i, "] = ", A[i]);
    }
}