From f184f2a9e9b34d043d05de26748e82f6f57b9255 Mon Sep 17 00:00:00 2001
From: Will Boyd <wbinventor@gmail.com>
Date: Wed, 11 May 2016 14:27:33 -0400
Subject: [PATCH] Added warning messages to Library for the correction and
 legendre_order properties

---
 openmc/mgxs/library.py | 14 ++++++++++++++
 openmc/mgxs/mgxs.py    |  6 +++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/openmc/mgxs/library.py b/openmc/mgxs/library.py
index f2a5c7569b..ea856d735c 100644
--- a/openmc/mgxs/library.py
+++ b/openmc/mgxs/library.py
@@ -297,12 +297,26 @@ class Library(object):
     @correction.setter
     def correction(self, correction):
         cv.check_value('correction', correction, ('P0', None))
+
+        if correction == 'P0' and self.legendre_order > 0:
+            msg = 'The P0 correction will be ignored since the scattering ' \
+                  'order {} is greater than zero'.format(self.legendre_order)
+            warnings.warn(msg)
+
         self._correction = correction
 
     @legendre_order.setter
     def legendre_order(self, legendre_order):
         cv.check_type('legendre_order', legendre_order, Integral)
         cv.check_greater_than('legendre_order', legendre_order, 0, equality=True)
+        cv.check_less_than('legendre_order', legendre_order, 10, equality=True)
+
+        if self.correction == 'P0' and legendre_order > 0:
+            msg = 'The P0 correction will be ignored since the scattering ' \
+                  'order {} is greater than zero'.format(self.legendre_order)
+            warnings.warn(msg, RuntimeWarning)
+            self.correction = None
+
         self._legendre_order = legendre_order
 
     @tally_trigger.setter
diff --git a/openmc/mgxs/mgxs.py b/openmc/mgxs/mgxs.py
index dc3d0d127b..830b6d7666 100644
--- a/openmc/mgxs/mgxs.py
+++ b/openmc/mgxs/mgxs.py
@@ -2034,11 +2034,15 @@ class ScatterMatrixXS(MGXS):
                subdomains='all', nuclides='all', moment='all',
                xs_type='macro', order_groups='increasing',
                row_column='inout', value='mean', **kwargs):
-        """Returns an array of multi-group cross sections.
+        r"""Returns an array of multi-group cross sections.
 
         This method constructs a 2D NumPy array for the requested scattering
         matrix data data for one or more energy groups and subdomains.
 
+        NOTE: The scattering moments are not multiplied by the :math:`(2l+1)/2`
+        prefactor in the expansion of the scattering source into Legendre
+        moments in the neutron transport equation.
+
         Parameters
         ----------
         in_groups : Iterable of Integral or 'all'