Fix MOAB partitioning for single a core

ci/recipe/meta.yaml

@@ -1,5 +1,5 @@
 {% set name = "pyremap" %}
-{% set version = "2.2.0" %}
+{% set version = "2.3.0" %}
 {% set python_min = "3.10" %}
 
 package:

docs/remapper/building_mapping.md

@@ -22,6 +22,9 @@ tool.
   not in your path.
 - `moab_path`: The path to the MOAB installation, if `mptempest` is not in
   your path.
+- `ntasks`: The number of MPI tasks to use to build the mapping file.  With
+  `ntasks=1`, the mapping tool is run in serial (without `parallel_exec`) and,
+  for `moab`, the meshes are not partitioned.
 - `parallel_exec`: The parallel executable (e.g. `srun` or `mpirun`) to use
   to run the mapping tool.  This may include additional flags, e.g.
   `srun --mpi=pmi2`.

pyremap/remapper/build_map.py

@@ -58,10 +58,10 @@ def _build_map(remapper, logger=None):
 
     elif map_tool == 'moab':
         moab_path = remapper.moab_path
-        src_scrip_filename = _moab_partition_scrip_file(
+        src_scrip_filename = _moab_convert_scrip_file(
             remapper, src_scrip_filename, moab_path, logger
         )
-        dst_scrip_filename = _moab_partition_scrip_file(
+        dst_scrip_filename = _moab_convert_scrip_file(
             remapper, dst_scrip_filename, moab_path, logger
         )
         args = _moab_build_map_args(
@@ -94,16 +94,16 @@ def _build_map(remapper, logger=None):
         tempobj.cleanup()
 
 
-def _moab_partition_scrip_file(remapper, in_filename, moab_path, logger):
+def _moab_convert_scrip_file(remapper, in_filename, moab_path, logger):
     """
-    Partition SCRIP file for parallel mbtempest use
+    Convert SCRIP file to HDF5 for mbtempest use, partitioning it if more than
+    one MPI task will be used
     """
     ntasks = remapper.ntasks
 
-    print(f'Partition SCRIP file {in_filename}')
+    print(f'Convert SCRIP file {in_filename}')
 
     h5m_filename = in_filename.replace('.nc', '.h5m')
-    h5m_part_filename = in_filename.replace('.nc', f'.p{ntasks}.h5m')
 
     if moab_path is None:
         mbconvert = 'mbconvert'
@@ -121,6 +121,17 @@ def _moab_partition_scrip_file(remapper, in_filename, moab_path, logger):
     ]
     check_call(args, logger=logger)
 
+    if ntasks == 1:
+        # nothing to partition (mbpart requires more than one part), so
+        # mbtempest reads the unpartitioned mesh.  The conversion above is
+        # still needed: mbtempest fails to compute weights when a mesh with
+        # more than 4 vertices per cell (e.g. an MPAS cell mesh) is loaded
+        # directly from SCRIP as the destination mesh.
+        print('  Done.')
+        return h5m_filename
+
+    h5m_part_filename = in_filename.replace('.nc', f'.p{ntasks}.h5m')
+
     # Partition source SCRIP
     args = [
         mbpart,

pyremap/version.py

@@ -1,2 +1,2 @@
-__version_info__ = (2, 2, 0)
+__version_info__ = (2, 3, 0)
 __version__ = '.'.join(str(vi) for vi in __version_info__)

tests/test_build_map.py

@@ -0,0 +1,178 @@
+# This software is open source software available under the BSD-3 license.
+#
+# Copyright (c) 2025 Triad National Security, LLC. All rights reserved.
+# Copyright (c) 2025 Lawrence Livermore National Security, LLC. All rights
+# reserved.
+# Copyright (c) 2025 UT-Battelle, LLC. All rights reserved.
+#
+# Additional copyright and license information can be found in the LICENSE file
+# distributed with this code, or at
+# https://raw.githubusercontent.com/MPAS-Dev/pyremap/main/LICENSE
+"""
+Unit tests for the commands pyremap builds to make mapping files.
+"""
+
+import os
+import shutil
+import tempfile
+from unittest import mock
+
+import numpy as np
+import pytest
+
+from pyremap import LatLonGridDescriptor, Remapper
+from tests import TestCase
+
+
+def _get_descriptors():
+    src_descriptor = LatLonGridDescriptor.create(
+        lat_corner=np.linspace(-90.0, 90.0, 46),
+        lon_corner=np.linspace(-180.0, 180.0, 91),
+        units='degrees',
+    )
+    dst_descriptor = LatLonGridDescriptor.create(
+        lat_corner=np.linspace(-90.0, 90.0, 91),
+        lon_corner=np.linspace(-180.0, 180.0, 181),
+        units='degrees',
+    )
+    return src_descriptor, dst_descriptor
+
+
+def _build_map_calls(ntasks, map_tool='moab', method='bilinear'):
+    """
+    Build a map with ``check_call`` mocked out, returning the list of argument
+    lists that would have been passed to ``check_call``
+    """
+    src_descriptor, dst_descriptor = _get_descriptors()
+    remapper = Remapper(
+        ntasks=ntasks,
+        map_tool=map_tool,
+        method=method,
+        src_descriptor=src_descriptor,
+        dst_descriptor=dst_descriptor,
+        use_tmp=False,
+    )
+    with mock.patch(
+        'pyremap.remapper.build_map.check_call'
+    ) as mock_check_call:
+        remapper.build_map()
+
+    return [call.args[0] for call in mock_check_call.call_args_list]
+
+
+class TestBuildMapArgs(TestCase):
+    """
+    Test the argument lists passed to the mapping tools, with ``check_call``
+    mocked out so no ESMF or MOAB binaries are needed.
+    """
+
+    def setUp(self):
+        self.test_dir = tempfile.mkdtemp()
+        self.cwd = os.getcwd()
+        os.chdir(self.test_dir)
+
+    def tearDown(self):
+        os.chdir(self.cwd)
+        shutil.rmtree(self.test_dir)
+
+    def test_moab_serial_does_not_partition(self):
+        """
+        ``mbpart`` cannot make a single partition, so it must not be called
+        when ``ntasks=1``
+        """
+        calls = _build_map_calls(ntasks=1)
+
+        executables = [os.path.basename(args[0]) for args in calls]
+        assert 'mbpart' not in executables
+
+        # the SCRIP files are still converted to HDF5, which mbtempest needs
+        assert executables == ['mbconvert', 'mbconvert', 'mbtempest']
+
+        mbtempest_args = calls[-1]
+        # no MPI launcher and the unpartitioned .h5m meshes are used
+        assert mbtempest_args[0].endswith('mbtempest')
+        loaded = [
+            mbtempest_args[index + 1]
+            for index, arg in enumerate(mbtempest_args)
+            if arg == '--load'
+        ]
+        assert loaded == ['src_mesh.h5m', 'dst_mesh.h5m']
+
+    def test_moab_parallel_partitions(self):
+        """
+        With more than one task, the meshes are partitioned with ``mbpart``
+        and mbtempest is launched with an MPI launcher
+        """
+        ntasks = 2
+        calls = _build_map_calls(ntasks=ntasks)
+
+        executables = [os.path.basename(args[0]) for args in calls]
+        assert executables == [
+            'mbconvert',
+            'mbpart',
+            'mbconvert',
+            'mbpart',
+            'mpirun',
+        ]
+
+        for args in calls:
+            if os.path.basename(args[0]) == 'mbpart':
+                assert args[1] == f'{ntasks}'
+
+        mbtempest_args = calls[-1]
+        assert mbtempest_args[:3] == ['mpirun', '-np', f'{ntasks}']
+        loaded = [
+            mbtempest_args[index + 1]
+            for index, arg in enumerate(mbtempest_args)
+            if arg == '--load'
+        ]
+        assert loaded == [
+            f'src_mesh.p{ntasks}.h5m',
+            f'dst_mesh.p{ntasks}.h5m',
+        ]
+
+    def test_esmf_serial(self):
+        """
+        The ESMF branch never partitions, whatever the task count
+        """
+        calls = _build_map_calls(ntasks=1, map_tool='esmf')
+
+        assert len(calls) == 1
+        assert os.path.basename(calls[0][0]) == 'ESMF_RegridWeightGen'
+
+
+@pytest.mark.parametrize('ntasks', [1, 2])
+def test_moab_serial_args_match_parallel(ntasks):
+    """
+    Whatever the task count, mbtempest gets the same weight-generation
+    options
+    """
+    cwd = os.getcwd()
+    test_dir = tempfile.mkdtemp()
+    os.chdir(test_dir)
+    try:
+        calls = _build_map_calls(ntasks=ntasks)
+    finally:
+        os.chdir(cwd)
+        shutil.rmtree(test_dir)
+
+    mbtempest_args = calls[-1]
+    start = mbtempest_args.index('--file')
+    assert mbtempest_args[start:] == [
+        '--file',
+        mbtempest_args[start + 1],
+        '--weights',
+        '--gnomonic',
+        '--boxeps',
+        '1e-9',
+        '--method',
+        'fv',
+        '--method',
+        'fv',
+        '--order',
+        '1',
+        '--order',
+        '1',
+        '--fvmethod',
+        'bilin',
+    ]