Allow MeshSource to take a 1D array of sources (#2980)

openmc/source.py

@@ -399,20 +399,19 @@ class MeshSource(SourceBase):
     ----------
     mesh : openmc.MeshBase
         The mesh over which source sites will be generated.
-    sources : iterable of openmc.SourceBase
-        Sources for each element in the mesh. If spatial distributions are set
-        on any of the source objects, they will be ignored during source site
-        sampling.
+    sources : sequence of openmc.SourceBase
+        Sources for each element in the mesh. Sources must be specified as
+        either a 1-D array in the order of the mesh indices or a
+        multidimensional array whose shape matches the mesh shape. If spatial
+        distributions are set on any of the source objects, they will be ignored
+        during source site sampling.
 
     Attributes
     ----------
     mesh : openmc.MeshBase
         The mesh over which source sites will be generated.
-    sources : numpy.ndarray or iterable of openmc.SourceBase
-        The set of sources to apply to each element. The shape of this array
-        must match the shape of the mesh with and exception in the case of
-        unstructured mesh, which allows for application of 1-D array or
-        iterable.
+    sources : numpy.ndarray of openmc.SourceBase
+        Sources to apply to each element
     strength : float
         Strength of the source
     type : str
@@ -433,7 +432,7 @@ class MeshSource(SourceBase):
 
     @property
     def strength(self) -> float:
-        return sum(s.strength for s in self.sources.flat)
+        return sum(s.strength for s in self.sources)
 
     @property
     def sources(self) -> np.ndarray:
@@ -450,16 +449,23 @@ class MeshSource(SourceBase):
 
         s = np.asarray(s)
 
-        if isinstance(self.mesh, StructuredMesh) and s.shape != self.mesh.dimension:
-            raise ValueError('The shape of the source array'
-                             f'({s.shape}) does not match the '
-                             f'dimensions of the structured mesh ({self.mesh.dimension})')
+        if isinstance(self.mesh, StructuredMesh):
+            if s.size != self.mesh.num_mesh_cells:
+                raise ValueError(
+                    f'The length of the source array ({s.size}) does not match '
+                    f'the number of mesh elements ({self.mesh.num_mesh_cells}).')
+
+            # If user gave a multidimensional array, flatten in the order
+            # of the mesh indices
+            if s.ndim > 1:
+                s = s.ravel(order='F')
+
         elif isinstance(self.mesh, UnstructuredMesh):
-            if len(s.shape) > 1:
+            if s.ndim > 1:
                 raise ValueError('Sources must be a 1-D array for unstructured mesh')
 
         self._sources = s
-        for src in self._sources.flat:
+        for src in self._sources:
             if isinstance(src, IndependentSource) and src.space is not None:
                 warnings.warn('Some sources on the mesh have spatial '
                               'distributions that will be ignored at runtime.')
@@ -481,7 +487,7 @@ class MeshSource(SourceBase):
         """
         current_strength = self.strength if self.strength != 0.0 else 1.0
 
-        for s in self.sources.flat:
+        for s in self.sources:
             s.strength *= strength / current_strength
 
     def normalize_source_strengths(self):
@@ -500,13 +506,8 @@ class MeshSource(SourceBase):
         elem.set("mesh", str(self.mesh.id))
 
         # write in the order of mesh indices
-        if isinstance(self.mesh, openmc.UnstructuredMesh):
-            for s in self.sources:
-                elem.append(s.to_xml_element())
-        else:
-            for idx in self.mesh.indices:
-                idx = tuple(i - 1 for i in idx)
-                elem.append(self.sources[idx].to_xml_element())
+        for s in self.sources:
+            elem.append(s.to_xml_element())
 
     @classmethod
     def from_xml_element(cls, elem: ET.Element, meshes) -> openmc.MeshSource:
@@ -527,11 +528,9 @@ class MeshSource(SourceBase):
             MeshSource generated from the XML element
         """
         mesh_id = int(get_text(elem, 'mesh'))
-
         mesh = meshes[mesh_id]
 
         sources = [SourceBase.from_xml_element(e) for e in elem.iterchildren('source')]
-        sources = np.asarray(sources).reshape(mesh.dimension, order='F')
         return cls(mesh, sources)
 
 

tests/unit_tests/test_source_mesh.py

@@ -276,12 +276,12 @@ def test_mesh_source_independent(run_in_tmpdir, void_model, mesh_type):
     # for each element, set a single-non zero source with particles
     # traveling out of the mesh (and geometry) w/o crossing any other
     # mesh elements
-    for i, j, k in mesh.indices:
+    for flat_index, (i, j, k) in enumerate(mesh.indices):
         ijk = (i-1, j-1, k-1)
         # zero-out all source strengths and set the strength
         # on the element of interest
         mesh_source.strength = 0.0
-        mesh_source.sources[ijk].strength = 1.0
+        mesh_source.sources[flat_index].strength = 1.0
 
         sp_file = model.run()
 
@@ -375,10 +375,7 @@ def test_mesh_source_file(run_in_tmpdir):
     mesh.upper_right = (2, 3, 4)
     mesh.dimension = (1, 1, 1)
 
-    mesh_source_arr = np.asarray([file_source]).reshape(mesh.dimension)
-    source = openmc.MeshSource(mesh, mesh_source_arr)
-
-    model.settings.source = source
+    model.settings.source = openmc.MeshSource(mesh, [file_source])
 
     model.export_to_model_xml()