-- one step of integration
stepEuler :: (Floating a) => a -> [a] -> [a]
stepEuler mu u@(x:xs) = (applyBC . (diffused mu)) $! u -- strict evaluation of u
    where
          diffused mu (left:x:[]) = []    -- ignore outer points
          diffused mu (left:x:right:xs) = -- integrate inner points
                   (x+mu*(left+right-2*x)) : diffused mu (x:right:xs)
          applyBC inner = inner `seq` u' `seq` l  `seq` r `seq` -- strict evaluation
                          (l ++ inner ++ r) -- boundary conditions
               where u' = [head u] ++ inner ++ [last u]
                     l = lbc u'
                     r = rbc u'
                     lbc = zeroflux mu             -- left boundary
                     rbc = (zeroflux mu) . reverse -- right boundary