The Data class is supplied by the user to hold the actual data that is to be stored in the nodes. Arithmetical operations on Data are expected to be supplied, as are two functions that perform sending and receiving of the Data in an MPI environment. Ideally, it should be possible to create the Data class without any knowledge of MPI. This would still require the user to supply the functions to pack and unpack the data that is to be sent as a message. For simplicity, this was not implemented, but to make to library easrier to use, it would be a valid addition.