Bug fixes

wrappers/python/simtk/openmm/app/gromacsgrofile.py

@@ -137,7 +137,7 @@ class GromacsGroFile(object):
                 xyz.append(Vec3(pos[0], pos[1], pos[2]))
             elif _is_gro_box(line) and ln == na + 2:
                 sline = line.split()
-                boxes.append([float(i) for i in sline]*nanometers)
+                boxes.append(tuple([float(i) for i in sline])*nanometers)
                 xyzs.append(xyz*nanometers)
                 xyz = []
                 ln = -1

wrappers/python/simtk/openmm/app/pdbfile.py

@@ -263,7 +263,7 @@ class PDBFile(object):
         if modelIndex is not None:
             print >>file, "MODEL     %4d" % modelIndex
         for (chainIndex, chain) in enumerate(topology.chains()):
-            chainName = chr(ord('A')+chainIndex)
+            chainName = chr(ord('A')+chainIndex%26)
             residues = list(chain.residues())
             for (resIndex, res) in enumerate(residues):
                 if len(res.name) > 3: