Read the periodicity flag from the YAML file

This gives more compatibility with Gadget. We can now run Gadget ICs straight out of the box without having to edit them to add this flag. That's an EAGLE-only convention which is more annoying than anything else.

Implements #466 (closed).

doc/RTD/source/InitialConditions/index.rst

@@ -117,15 +117,6 @@ GADGET-2 based analysis programs:
 + ``Time``, time of the start of the simulation in internal units or expressed
   as a scale-factor for cosmological runs. SWIFT ignores this and reads it from
   the parameter file.
-  
-RuntimePars
-~~~~~~~~~~~
-
-In the ``/RuntimePars/``, the following attributes are required:
-
-+ ``PeriodicBoundariesOn``, a flag to tell the code whether or not you
-  have periodic boundaries switched on. Again, this is historical; it should be
-  set to 1 (default) if you have the code running in periodic mode, or 0 otherwise.
 
 
 Particle Data
@@ -145,7 +136,7 @@ individual particle type (e.g. ``/PartType0/``) that have the following *dataset
   velocities divided by ``sqrt(a)`` (see below for a fix).
 + ``ParticleIDs``, an array of length N that are unique identifying numbers for
   each particle. Note that these have to be unique to a particle, and cannot be
-  the same even between particle types. The **IDs must be >1**. 0 or negative
+  the same even between particle types. The **IDs must be >= 0**. Negative
   IDs will be rejected by the code.
 + ``Masses``, an array of length N that gives the masses of the particles.
 
@@ -214,8 +205,6 @@ You should have an HDF5 file with the following structure:
      Flag_Entropy_ICs=0
      NumPart_Total=[0, 1, 0, 0, 4, 5]
      NumPart_Total_HighWord=[0, 0, 0, 0, 0, 0]
-   RuntimePars/
-     PeriodicBoundariesOn=1
    Units/
      Unit current in cgs (U_I)=1.0
      Unit length in cgs (U_L)=1.0