fix for when ordering attribute not in PeriodicTorsionForce element

ce3a5dc0 · Rafal P. Wiewiora · aaf535b8 · ce3a5dc0
Commit ce3a5dc0 authored Aug 25, 2016 by Rafal P. Wiewiora
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wrappers/python/simtk/openmm/app/forcefield.py wrappers/python/simtk/openmm/app/forcefield.py +4 -1

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--- a/wrappers/python/simtk/openmm/app/forcefield.py
+++ b/wrappers/python/simtk/openmm/app/forcefield.py
@@ -1840,7 +1840,10 @@ class PeriodicTorsionGenerator(object):
        for torsion in element.findall('Proper'):
            generator.registerProperTorsion(torsion.attrib)
        for torsion in element.findall('Improper'):
-            generator.registerImproperTorsion(torsion.attrib, element.attrib['ordering'])
+            if 'ordering' in element.attrib:
+                generator.registerImproperTorsion(torsion.attrib, element.attrib['ordering'])
+            else:
+                generator.registerImproperTorsion(torsion.attrib)

    def createForce(self, sys, data, nonbondedMethod, nonbondedCutoff, args):
        existing = [sys.getForce(i) for i in range(sys.getNumForces())]