Programmer Guide Sample Code Fix

[Alexander Ding]

This is a very small detail. On page 9 of the Programmer's Guide, the code for a red-black solver

for (long stepi = 0; stepi < MAX_ITER; stepi++) {
  // alternate between red and black
  int start = stepi % 2;
  // get the values for the ghost cells
  if (!start) u[0] = upcxx::rget(uL + block).wait();
  else u[n_local - 1] = upcxx::rget(uR + 1).wait();
  // some more stuff

Doesn't fill in the ghost cell of both ends in each iteration. If block is even this would be fine, but if block is odd this results in not updating the value of a ghost cell that is used for computation.

It's not a big deal, but it's kind of confusing to a new reader.

[Dan Bonachea]

Hi @alexding123 - thanks for the note.

I agree this code is assuming block is even and that should be stated.

Proposed fix in pull request #85

[Dan Bonachea]

issue213: Clarify assumption in PG red/black example

Resolves issue #213

→ <<cset 34bda475b5a0>>