README.md

FastOutput class

Provides a convenient interface to save high-time-resolution output at a few points from a BOUT++ simulation. Gets run-time options by default from the [fast_output] section. Can produce output every internal timestep (fastest possible rate, but not regular), by setting type = timestep or at a fixed multiple of the output timestep, by setting type = monitor. [Warning: if the resulting monitor timestep is not long enough to contain many internal timesteps then performance may be significantly impacted.] To use, add a FastOutput member to your PhysicsModel. Also need to add fields and a position given by global indices to the object. For example, to read an arbitrary number of points as fractions of the box size from options, and add density and temperature at those points to FastOutput fast_output, you could add the following to your init() method.

// Set up output for synthetic Langmuir probe trace
if (fast_output.enabled) {

  // Add monitor if necessary
  if (fast_output.enable_monitor) {
    solver->addMonitor(&fast_output);
  }

  // Add points from the input file
  int i = 0;
  BoutReal xpos, ypos, zpos;
  int ix, iy, iz;
  Options* fast_output_options = Options::getRoot()->getSection("fast_output");
  while (true) {
    // Add more points if explicitly set in input file
    fast_output_options->get("xpos"+std::to_string(i), xpos, -1.);
    fast_output_options->get("ypos"+std::to_string(i), ypos, -1.);
    fast_output_options->get("zpos"+std::to_string(i), zpos, -1.);
    if (xpos<0. || ypos<0. || zpos<0.) {
      output.write("\tAdded %i fast_output points\n", i);
      break;
    }
    ix = int(xpos*mesh->GlobalNx);
    iy = int(ypos*mesh->GlobalNy);
    iz = int(zpos*mesh->GlobalNz);
    fast_output.add("n"+std::to_string(i), n, ix, iy, iz);
    fast_output.add("T"+std::to_string(i), T, ix, iy, iz);
    i++;
  }
}

Output is written to one (or several, if necessary) separate netCDF files, named BOUT.fast.i.nc by default (where i is the index of the processor writing output).