=== modified file 'ufl/mathfunctions.py'
--- ufl/mathfunctions.py	2013-03-04 16:12:31 +0000
+++ ufl/mathfunctions.py	2013-03-15 04:27:04 +0000
@@ -161,7 +161,7 @@
     __slots__ = ()
     def __new__(cls, argument):
         if isinstance(argument, (ScalarValue, Zero)):
-            return FloatValue(math.cos(float(argument)))
+            return FloatValue(math.cosh(float(argument)))
         return MathFunction.__new__(cls)
 
     def __init__(self, argument):