Merge branch 'main' of github.com:EXP-code/EXP-docs

Author: Martin D. Weinberg

index.rst

@@ -89,6 +89,7 @@ EXP concepts
    topics/bfetheory
    topics/codeintro
    topics/timesseries
+   topics/units
    topics/multistep
    topics/centering
    topics/yamlconfig
@@ -106,6 +107,9 @@ mathematics used in EXP.
 :doc:`topics/timesseries`
     Descriptions for methods to analyze BFE time series
 
+:doc:`topics/units`
+    Physical units in EXP 
+
 :doc:`topics/multistep`
     A quick review of EXP's ODE solver and multi time step ladder
 

intro/overview.rst

@@ -96,6 +96,11 @@ Here's the code for computing coefficients::
      #
      coef = basis.createFromArray(data[:,0], data[:,1:4], time=3.0)
 
+     # Add your simulation units (we assume a unit-free simulation here)
+     #
+     coef.setUnits([('mass', 'none', 1.0), ('length', 'none', 1.0),
+     ('time', 'none', 1.0), ('G', 'none', 1.0)])
+
      # Make an HDF5 file
      #
      coefs = pyEXP.coefs.Coefs.makecoefs(coef)
@@ -144,6 +149,11 @@ More detailed information on YAML and config parameters is available
 in the :ref:`What is YAML?<yamlconfig>` and :ref:`How to visualize the
 BFE bases used to make your coefficients<visualizing-bases>` pages.
 
+The unit system in EXP is described in more detail in :ref:`Units in
+EXP and pyEXP<units>`.  For this example, we assume a unit-free
+simulation but it's easy to add any unit system that is convenient for
+you.
+
 pyEXP is then ready to make the coefficients from your phase-space
 data.  This example assumes that the mass and positions of your
 particles are in columns 1, 2, 3, 4 of the file and that the positions