include link to swarm packs

Author: lroberts36

doc/sphinx/src/particles.rst

@@ -151,14 +151,16 @@ Similarly to grid variables, particle swarms support
 This also supports ``FlatIdx`` for indexing; see the
 ``particle_leapfrog`` example for usage.
 
-``SwarmPack``s
-----------------
+. _swarm_packs:
+
+``SwarmPack``\ s
+--------------
 
-Similar to grid variables, swarms can be packed over ``MeshBlock``s via ``SwarmPack``s.
-``SwarmPack``s are the particle analog to ``SparsePack``s for field variables.  A single
+Similar to grid variables, swarms can be packed over ``MeshBlock``\ s via ``SwarmPack``\ s.
+``SwarmPack``\ s are the particle analog to ``SparsePack``\ s for field variables.  A single
 ``SwarmPack`` can contain either ``int`` or ``Real`` entries, but not both.  One can pack
 a ``SwarmPack`` via a ``std::vector<std::string>`` or the type-based variable prescription
-previously used by ``SparsePack``s.
+previously used by ``SparsePack``\ s (see :ref:`sparse_packs`).
 
 For packing via string (wherein below, ``swarm_position::x::name()`` returns a string),
 one must specify the data type by template argument:

doc/sphinx/src/sparse_packs.rst

@@ -16,6 +16,7 @@ etc. within a kernel.
 
 ``SparsePack``\ *s work for all types of variables (both dense and sparse). They were originally implemented to support sparse variables and to supersede the older* ``VariablePack``\ *s and* ``VariableFluxPack``\ *s and picked up the* ``Sparse`` *modifier to differentiate them. The latter have not been removed from ``Parthenon`` because some downstream codes still rely on them, but they are deprecated and will be removed eventually.*
 
+*If you want to deal with particle fields, you will need to use* ``SwarmPack``\ *s, which are described at :ref:`swarm_packs`.
 Type-based Packing
 ------------------