dsOut = catObservations(dataSet1,dataSet2)
    Return a data set, dsOut, created by concatenating the
    data and observationInfo in dataSet1 and dataSet2.  The
    output data set, dsOut, will have nObservations =
    dataSet1.nObservations + dataSet2.nObservations.
 

Help for prtDataSetRegress/catObservations is inherited from superclass prtDataSetBase