  The efficiency of path sampling simulations can be improved considerably
using the approach of path swapping. For this purpose, we have devised a new
algorithmic procedure based on the transition interface sampling technique. In
the same spirit of parallel tempering, paths between different ensembles are
swapped, but the role of temperature is here played by the interface position.
We have tested the method on the denaturation transition of DNA using the
Peyrard-Bishop-Dauxois model. We find that the new algorithm gives a reduction
of the computational cost by a factor 20.
