Merge pull request #2154 from shimwell/adding_log_width_bins_to_energ…

…y_filter

added bin_log_width to EnergyFilter() to help with plotting

openmc/filter.py

@@ -1324,6 +1324,18 @@ def check_bins(self, bins):
             cv.check_greater_than('filter value', v0, 0., equality=True)
             cv.check_greater_than('filter value', v1, 0., equality=True)
 
+    @property
+    def lethargy_bin_width(self):
+        """Calculates the base 10 log width of energy bins which is useful when
+        plotting the normalized flux.
+
+        Returns
+        -------
+        numpy.array
+            Array of bin widths
+        """
+        return np.log10(self.bins[:, 1]/self.bins[:, 0])
+
     @classmethod
     def from_group_structure(cls, group_structure):
         """Construct an EnergyFilter instance from a standard group structure.

tests/unit_tests/test_filters.py

@@ -1,3 +1,4 @@
+import math
 import numpy as np
 import openmc
 from pytest import fixture, approx
@@ -246,3 +247,11 @@ def test_energy():
     f = openmc.EnergyFilter.from_group_structure('CCFE-709')
     assert f.bins.shape == (709, 2)
     assert len(f.values) == 710
+
+
+def test_lethargy_bin_width():
+    f = openmc.EnergyFilter.from_group_structure('VITAMIN-J-175')
+    assert len(f.lethargy_bin_width) == 175
+    energy_bins = openmc.mgxs.GROUP_STRUCTURES['VITAMIN-J-175'] 
+    assert f.lethargy_bin_width[0] == math.log10(energy_bins[1]/energy_bins[0])
+    assert f.lethargy_bin_width[-1] == math.log10(energy_bins[-1]/energy_bins[-2])