example.rst

Worked-out example

The default options in the code generate a very low-resolution 3d cube of Q values with the sample dataset included with the code. Running the code with those options using the commands listed below, generates the following 3d view in ParaView, which includes a magnetogram, volumetric rendering of Q values, as well as traced field lines:

The command lines below show a typical sequence of commands to generate a 3d data cube of Q values, and then visualize the result. The example uses the data files distributed with the code and was run on the CPU of a low-end laptop. The calculation of about half a million Q values, post-processing and rendering took less than 5 minutes with the default settings. Note that in the session below, qslSquasher was killed after two mesh refinements.

$ time ./compile.sh

  real  0m20.256s
  user  0m19.788s
  sys   0m0.393s

$ time ./qslSquasher > raw.dat
  1. pthread-Intel(R) Core(TM) i7-8650U CPU @ 1.90GHz (Portable Computing Language)

  Calculating current ...
  ... done.
  Analyzing transverse FL motions ...
  ... done.
  Reading successful.
  Integration step set at 0.022446 Mm
  Initialization successful.
  Number of field lines to be integrated in this mesh refinement step: 262144
  Beginning FORWARD integration along field lines ...
  # of computed field lines = 0 out of 242172 in mesh refinement: 0
     ... skipping lines ...
  # of computed field lines = 242166 out of 242172 in mesh refinement: 0
  Beginning BACKWARD integration along field lines ...
  # of computed field lines = 0 out of 242172 in mesh refinement: 0
     ... skipping lines ...
  # of computed field lines = 242166 out of 242172 in mesh refinement: 0
  Quantities calculated successfully.
  Starting sort...
  ... done sorting.
  Starting sort...
  ... done sorting.
  Number of field lines to be integrated in this mesh refinement step: 265381
  Beginning FORWARD integration along field lines ...
  # of computed field lines = 0 out of 265223 in mesh refinement: 1
     ... skipping lines ...
  # of computed field lines = 265221 out of 265223 in mesh refinement: 1
  Beginning BACKWARD integration along field lines ...
  # of computed field lines = 0 out of 265223 in mesh refinement: 1
     ... skipping lines ...
  # of computed field lines = 265222 out of 265223 in mesh refinement: 1
  Quantities calculated successfully.
  Starting sort...
  ... done sorting.
  Starting sort...
  ... done sorting.
  Number of field lines to be integrated in this mesh refinement step: 557436
  Beginning FORWARD integration along field lines ...
  # of computed field lines = 0 out of 556914 in mesh refinement: 2
     ... skipping lines ...
  # of computed field lines = 3897603 out of 3897606 in mesh refinement: 5
  Quantities calculated successfully.
  ^C

  real  19m46.221s
  user  119m21.692s
  sys   2m16.436s
$ time ./snapshot > grid3d.dat

  real  0m12.897s
  user  0m12.611s
  sys   0m0.260s
$ time python viz3d.py

  real  0m19.614s
  user  0m18.337s
  sys   0m1.218s
$ paraview --state=viz3d_paraview.pvsm

The example above is for input in cartesian coordinates. It generates several output files:

• :file:`raw.dat` contains the raw output from :download:`qslSquasher.cpp`.
• :file:`grid3d.dat` is the result of the first post-processing step done by :download:`snapshot.cpp`.
• :file:`Global_Quantities.vtr` is a VTK file, containing the rectilinear grid of global quantities in cartesian coordinates.
• :file:`Local_Quantities.vtr` is a VTK file, containing the rectilinear grid of local quantities in cartesian coordinates. This file is generated from the input files used by qslSquasher.

The last two files are used by the included :download:`ParaView session file <viz3d_paraview.pvsm>` to generate the figure shown in the beginning of this section.