Merge branch 'develop' into xml

Conflicts:
	src/DEPENDENCIES
	src/input_xml.F90
	src/templates/settings_t.xml

docs/source/usersguide/input.rst

@@ -405,6 +405,15 @@ integers: the batch number, generation number, and particle number.
 
   *Default*: None
 
+.. _track:
+
+``<track>`` Element
+-------------------
+
+The ``<track>`` element specifies particles for which OpenMC will output binary files describing particle position at every step of its transport. This element should be followed by triplets of integers.  Each triplet describes one particle.  The integers in each triplet specify the batch number, generation number, and particle number, respectively.
+
+  *Default*: None
+
 ``<uniform_fs>`` Element
 ------------------------
 

docs/source/usersguide/install.rst

@@ -358,6 +358,7 @@ OpenMC accepts the following command line flags:
 -r, --restart file     Restart a previous run from a state point or a particle
                        restart file
 -s, --threads N        Run with *N* OpenMP threads
+-t, --track            Write tracks for all particles
 -v, --version          Show version information
 
 -----------------------------------------------------

docs/source/usersguide/processing.rst

@@ -353,9 +353,41 @@ file. Note that the data contained in the output from
 ``StatePoint.extract_result`` is already in a Numpy array that can be reshaped
 and dumped to MATLAB in one step.
 
+----------------------------
+Particle Track Visualization
+----------------------------
 
+.. image:: ../../img/Tracks.png
+   :height: 200px
 
+OpenMC can dump particle tracks—the position of particles as they are
+transported through the geometry.  There are two ways to make OpenMC output
+tracks: all particle tracks through a commandline argument or specific particle
+tracks through settings.xml.
 
+Running OpenMC with the argument "-t", "-track", or "--track" will cause a track
+file to be created for every particle transported in the code.
 
+The settings.xml file can dictate that specific particle tracks are output.
+These particles are specified withen a ''track'' element.  The ''track'' element
+should contain triplets of integers specifying the batch, generation, and
+particle numbers, respectively.  For example, to output the tracks for particles
+3 and 4 of batch 1 and generation 2 the settings.xml file should contain:
 
+.. code-block:: xml
 
+      <track>
+        1 2 3
+        1 2 4
+      </track>
+
+After running OpenMC, the directory should contain a file of the form
+"track_(batch #)_(generation #)_(particle #).(binary or h5)" for each particle
+tracked.  These track files can be converted into VTK poly data files with the
+"track.py" utility.  The usage of track.py is of the form "track.py [-o OUT] IN"
+where OUT is the optional output filename and IN is one or more filenames
+describing track files.  The default output name is "track.pvtp".  A common
+usage of track.py is "track.py track*.binary" which will use the data from all
+binary track files in the directory to write a "track.pvtp" VTK output file.
+The .pvtp file can then be read and plotted by 3d visualization programs such as
+Paraview.