Method needs_P

src/susceptibility.cpp:76–82

Return whether or not we need to allocate P[c][cmp]. (We don't need to allocate P[c] if we can be sure it will be zero.) We are a bit wasteful because if sigma is nontrivial in *any* chunk, we allocate the corresponding P on *every* owned chunk. This greatly simplifies communication in boundaries.cpp, because we can be sure that one chunk has a P then any chunk it borders has the

   TODO: reduce memory usage (bookkeeping seem much harder, though).
*/
bool susceptibility::needs_P(component c, int cmp, realnum *W[NUM_FIELD_COMPONENTS][2]) const {
  if (!is_electric(c) && !is_magnetic(c)) return false;
  FOR_DIRECTIONS(d) {
    if (!trivial_sigma[c][d] && W[direction_component(c, d)][cmp]) return true;
  }
  return false;
}

/* return whether we need the notowned parts of the W field --
   by default, this is only the case if sigma has offdiagonal components