Merge pull request #1374 from pshriwise/volume_trigger

Volume Calculation Trigger

docs/source/io_formats/volume.rst

@@ -23,6 +23,8 @@ The current version of the volume file format is 1.0.
                bounding box
              - **upper_right** (*double[3]*) -- Upper-right coordinates of
                bounding box
+             - **threshold** (*double*) -- Threshold used for volume uncertainty
+             - **trigger_type** (*char[]*) -- Trigger type used for volume uncertainty
 
 **/domain_<id>/**
 

docs/source/usersguide/volume.rst

@@ -37,6 +37,16 @@ arguments are not necessary. For example,
 Of course, the volumes that you *need* this capability for are often the ones
 with complex definitions.
 
+A threshold can be applied for the calculation's variance, standard deviation,
+or relative error of volume estimates using :meth:`openmc.VolumeCalculation.set_trigger`::
+
+    vol_calc.set_trigger(1e-05, 'std_dev')
+
+If a threshold is provided, calculations will be performed iteratively using the
+number of samples specified on the calculation until all volume uncertainties are below
+the threshold value. If no threshold is provided, the calculation will run the number of
+samples specified once and return the result.
+
 Once you have one or more :class:`openmc.VolumeCalculation` objects created, you
 can then assign then to :attr:`Settings.volume_calculations`::