Addressing comments from @paulromano

docs/source/io_formats/settings.rst

@@ -1050,6 +1050,12 @@ sub-elements/attributes:
 
     *Default*: 3.0
 
+  :max_lower_bound_ratio:
+    Maximum allowed ratio of a particle's weight to the weight window's lower
+    bound. A factor will be applied to raise the weight window to be lower than
+	  the particle's weight by a factor of max_lower_bound_ratio during transport
+    if exceeded.
+
   :max_split:
     Maximum allowable number of particles when splitting
 

include/openmc/particle_data.h

@@ -310,8 +310,7 @@ private:
 
   // Weight window information
   int n_split_ {0}; // Number of times this particle has been split
-  // Particle-specific factor for on-the-fly weight window adjustment
-  double ww_factor_ {0.0};
+  double ww_factor_ {0.0}; // Particle-specific factor for on-the-fly weight window adjustment
 
 // DagMC state variables
 #ifdef DAGMC

openmc/weight_windows.py

@@ -48,11 +48,11 @@ class WeightWindows(IDManagerMixin):
     survival_ratio : float
         Ratio of the survival weight to the lower weight window bound for
         rouletting
-    max_lower_bound_ratio: float
+    max_lower_bound_ratio : float
         Maximum allowed ratio of a particle's weight to the weight window's
 	lower bound. A factor will be applied to raise the weight window to
 	be lower than the particle's weight by a factor of max_lower_bound_ratio
-        during transport if exceeded. Only applied if > 1.0. (Default: 1.0).
+        during transport if exceeded.
     max_split : int
         Maximum allowable number of particles when splitting
     weight_cutoff : float
@@ -99,7 +99,8 @@ class WeightWindows(IDManagerMixin):
 
     def __init__(self, mesh, lower_ww_bounds, upper_ww_bounds=None,
                  upper_bound_ratio=None, energy_bins=None, particle_type='neutron',
-                 survival_ratio=3, max_lb_ratio=1.0, max_split=10, weight_cutoff=1.e-38, id=None):
+                 survival_ratio=3, max_lower_bound_ratio=None, max_split=10,
+                 weight_cutoff=1.e-38, id=None):
         self.mesh = mesh
         self.id = id
         self.particle_type = particle_type
@@ -129,7 +130,8 @@ class WeightWindows(IDManagerMixin):
                              'do not match')
 
         self.survival_ratio = survival_ratio
-        self.max_lower_bound_ratio = max_lb_ratio
+        if self.max_lower_bound_ratio is not None:
+            self.max_lower_bound_ratio = max_lower_bound_ratio
         self.max_split = max_split
         self.weight_cutoff = weight_cutoff
 
@@ -260,8 +262,9 @@ class WeightWindows(IDManagerMixin):
         subelement = ET.SubElement(element, 'survival_ratio')
         subelement.text = str(self.survival_ratio)
 
-        subelement = ET.SubElement(element, 'max_lower_bound_ratio')
-        subelement.text = str(self.max_lower_bound_ratio)
+        if self.max_lower_bound_ratio is not None:
+            subelement = ET.SubElement(element, 'max_lower_bound_ratio')
+            subelement.text = str(self.max_lower_bound_ratio)
 
         subelement = ET.SubElement(element, 'max_split')
         subelement.text = str(self.max_split)
@@ -300,7 +303,11 @@ class WeightWindows(IDManagerMixin):
         ebins = [float(b) for b in get_text(elem, 'energy_bins').split()]
         particle_type = get_text(elem, 'particle_type')
         survival_ratio = float(get_text(elem, 'survival_ratio'))
-        max_lb_ratio = float(get_text(elem, 'max_lower_bound_ratio'))
+
+        max_lower_bound_ratio = None
+        if get_text(elem, 'max_lower_bound_ratio'):
+            max_lower_bound_ratio = float(get_text(elem, 'max_lower_bound_ratio'))
+
         max_split = int(get_text(elem, 'max_split'))
         weight_cutoff = float(get_text(elem, 'weight_cutoff'))
         id = int(get_text(elem, 'id'))
@@ -312,7 +319,7 @@ class WeightWindows(IDManagerMixin):
             energy_bins=ebins,
             particle_type=particle_type,
             survival_ratio=survival_ratio,
-            max_lb_ratio=max_lb_ratio,
+            max_lower_bound_ratio=max_lower_bound_ratio,
             max_split=max_split,
             weight_cutoff=weight_cutoff,
             id=id
@@ -342,7 +349,11 @@ class WeightWindows(IDManagerMixin):
         lower_ww_bounds = group['lower_ww_bounds'][()]
         upper_ww_bounds = group['upper_ww_bounds'][()]
         survival_ratio = group['survival_ratio'][()]
-        max_lb_ratio = group['max_lower_bound_ratio'][()]
+
+        max_lower_bound_ratio = None
+        if group.get('max_lower_bound_ratio') is not None:
+            max_lower_bound_ratio = group['max_lower_bound_ratio'][()]
+
         max_split = group['max_split'][()]
         weight_cutoff = group['weight_cutoff'][()]
 
@@ -353,7 +364,7 @@ class WeightWindows(IDManagerMixin):
             energy_bins=ebins,
             particle_type=ptype,
             survival_ratio=survival_ratio,
-            max_lb_ratio=max_lb_ratio,
+            max_lower_bound_ratio=max_lower_bound_ratio,
             max_split=max_split,
             weight_cutoff=weight_cutoff,
             id=id