Writing interpolation attribute as an attribute of the 'y' dataset.

docs/source/io_formats/statepoint.rst

@@ -108,8 +108,9 @@ The current version of the statepoint file format is 17.0.
              interpolation. Only used for 'energyfunction' filters.
            - **y** (*double[]*) -- Interpolant values for energyfunction
              interpolation. Only used for 'energyfunction' filters.
-           - **interpolation** (*int*) -- Interpolation type. Only used for
-             'energyfunction' filters.
+
+             :Attributes: - **interpolation** (*int*) -- Interpolation type. Only used for
+                            'energyfunction' filters.
 
 **/tallies/derivatives/derivative <id>/**
 

openmc/filter.py

@@ -1967,13 +1967,14 @@ class EnergyFunctionFilter(Filter):
                              + group['type'][()].decode() + " instead")
 
         energy = group['energy'][()]
-        y = group['y'][()]
+        y_grp = group['y']
+        y = y_grp[()]
         filter_id = int(group.name.split('/')[-1].lstrip('filter '))
 
         out = cls(energy, y, filter_id=filter_id)
-        if 'interpolation' in group:
+        if 'interpolation' in y_grp.attrs:
             out.interpolation =  \
-                cls.INTERPOLATION_SCHEMES[group['interpolation'][()]]
+                cls.INTERPOLATION_SCHEMES[y_grp.attrs['interpolation'][()]]
 
         return out
 

src/tallies/filter_energyfunc.cpp

@@ -104,8 +104,9 @@ void EnergyFunctionFilter::to_statepoint(hid_t filter_group) const
   Filter::to_statepoint(filter_group);
   write_dataset(filter_group, "energy", energy_);
   write_dataset(filter_group, "y", y_);
-  write_dataset(
-    filter_group, "interpolation", static_cast<int>(interpolation_));
+  hid_t y_dataset = open_dataset(filter_group, "y");
+  write_attribute<int>(y_dataset, "interpolation", static_cast<int>(interpolation_));
+  close_dataset(y_dataset);
 }
 
 std::string EnergyFunctionFilter::text_label(int bin) const