Parallel operator

To understand this section it useful to refer to Clapp (2004). If an operator is in fact a parallel operator then the SEP.operator.oc_par class should be used. This class inherits from the SEP.operator.oc. The parallel operator is initialized with a parallel job object. It expects the domain and range vectors to have been specified in the job creation with the keys `domain' and `range'. The forward and adjoint operation function are defined in the same manner described above with the exception that domain and range vectors are turned into parfile objects and running the job involves executing parjob.run.