Remove MPI related code, tests and docs

docs/getting_started/tutorial_output.ipynb

@@ -162,9 +162,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Note that if you are running Parcels on multiple processors with `mpirun`, you will need to concatenate the files of each processor, see also the [MPI documentation](https://docs.oceanparcels.org/en/latest/examples/documentation_MPI.html#Reading-in-the-ParticleFile-data-in-zarr-format).\n",
-    "\n",
-    "Also, once you have loaded the data as an `xarray` DataSet using `xr.open_zarr()`, you can always save the file to NetCDF if you prefer with the `.to_netcdf()` method.\n"
+    "Once you have loaded the data as an `xarray` DataSet using `xr.open_zarr()`, you can always save the file to NetCDF if you prefer with the `.to_netcdf()` method.\n"
    ]
   },
   {

docs/user_guide/examples_v3/documentation_LargeRunsOutput.ipynb

@@ -60,7 +60,7 @@
    "id": "4",
    "metadata": {},
    "source": [
-    "## How to save the output of an MPI ocean parcels run to a single zarr dataset\n"
+    "## (TODO: Remove section now that we don't support MPI) How to save the output of an MPI ocean parcels run to a single zarr dataset\n"
    ]
   },
   {

docs/user_guide/examples_v3/example_stommel.py

@@ -88,11 +88,6 @@ def AgeP(particle, fieldset, time):  # pragma: no cover
         particle.delete()
 
 
-def simple_partition_function(coords, mpi_size=1):
-    """A very simple partition function that assigns particles to processors (for MPI testing purposes))"""
-    return np.linspace(0, mpi_size, coords.shape[0], endpoint=False, dtype=np.int32)
-
-
 def stommel_example(
     npart=1,
     verbose=False,
@@ -101,7 +96,6 @@ def stommel_example(
     outfile="StommelParticle.zarr",
     repeatdt=None,
     maxage=None,
-    custom_partition_function=False,
 ):
     parcels.timer.fieldset = parcels.timer.Timer(
         "FieldSet", parent=parcels.timer.stommel
@@ -125,27 +119,15 @@ def stommel_example(
     ]
     MyParticle = parcels.Particle.add_variables(extra_vars)
 
-    if custom_partition_function:
-        pset = parcels.ParticleSet.from_line(
-            fieldset,
-            size=npart,
-            pclass=MyParticle,
-            repeatdt=repeatdt,
-            start=(10e3, 5000e3),
-            finish=(100e3, 5000e3),
-            time=0,
-            partition_function=simple_partition_function,
-        )
-    else:
-        pset = parcels.ParticleSet.from_line(
-            fieldset,
-            size=npart,
-            pclass=MyParticle,
-            repeatdt=repeatdt,
-            start=(10e3, 5000e3),
-            finish=(100e3, 5000e3),
-            time=0,
-        )
+    pset = parcels.ParticleSet.from_line(
+        fieldset,
+        size=npart,
+        pclass=MyParticle,
+        repeatdt=repeatdt,
+        start=(10e3, 5000e3),
+        finish=(100e3, 5000e3),
+        time=0,
+    )
 
     if verbose:
         print(f"Initial particle positions:\n{pset}")
@@ -245,12 +227,6 @@ def main(args=None):
         type=int,
         help="max age of the particles (after which particles are deleted)",
     )
-    p.add_argument(
-        "-cpf",
-        "--custom_partition_function",
-        default=False,
-        help="Use a custom partition_function (for MPI testing purposes)",
-    )
     args = p.parse_args(args)
 
     parcels.timer.args.stop()
@@ -262,7 +238,6 @@ def main(args=None):
         outfile=args.outfile,
         repeatdt=args.repeatdt,
         maxage=args.maxage,
-        custom_partition_function=args.custom_partition_function,
     )
     parcels.timer.stommel.stop()
     parcels.timer.root.stop()

src/parcels/_compat.py

@@ -1,23 +1,5 @@
 """Import helpers for compatability between installations."""
 
-__all__ = ["MPI", "KMeans"]
-
-from typing import Any
-
-MPI: Any | None = None
-KMeans: Any | None = None
-
-try:
-    from mpi4py import MPI  # type: ignore[import-untyped,no-redef]
-except ModuleNotFoundError:
-    pass
-
-# KMeans is used in MPI. sklearn not installed by default
-try:
-    from sklearn.cluster import KMeans
-except ModuleNotFoundError:
-    pass
-
 
 # for compat with v3 of parcels when users provide `initial=attrgetter("lon")` to a Variable
 # so that particle initial state matches another variable

src/parcels/_core/particleset.py

@@ -51,8 +51,6 @@ class ParticleSet:
         Optional interval on which to repeat the release of the ParticleSet. Either timedelta object, or float in seconds.
     trajectory_ids :
         Optional list of "trajectory" values (integers) for the particle IDs
-    partition_function :
-        Function to use for partitioning particles over processors. Default is to use kMeans
 
         Other Variables can be initialised using further arguments (e.g. v=... for a Variable named 'v')
     """
@@ -106,11 +104,8 @@ def __init__(
             _warn_particle_times_outside_fieldset_time_bounds(time, fieldset.time_interval)
 
         for kwvar in kwargs:
-            if kwvar not in ["partition_function"]:
-                kwargs[kwvar] = np.array(kwargs[kwvar]).flatten()
-                assert lon.size == kwargs[kwvar].size, (
-                    f"{kwvar} and positions (lon, lat, z) don't have the same lengths."
-                )
+            kwargs[kwvar] = np.array(kwargs[kwvar]).flatten()
+            assert lon.size == kwargs[kwvar].size, f"{kwvar} and positions (lon, lat, z) don't have the same lengths."
 
         self._data = create_particle_data(
             pclass=pclass,