Communicating Multi-dimensional arrays using MPJ Express

Many scientific applications utilize multi-dimensional arrays for storing data. Naturally in the parallel versions, there is a frequent requirement of communicating these multi-dimensional arrays.

Currently the MPJ Express version "directly" supports communicating basic datatypes to and from single dimension arrays. But, it is obviously possible to communicate multiple dimension arrays. Here we'll see how 2D arrays are communicated using the MPJ Express software.

There are mainly two ways of communicating 2D arrays. The first is to communicate this data using the MPI.OBJECT datatype. The second is to map (or flatten) the 2D array onto a 1D array and communicate normally. If you are looking for performance, the second option is recommended. The main reason is performance, the first option is severely hampered by the performance of Java's serialization.

The MultidimMatrix class communicates data from the 2D array using the MPI.OBJECT datatype.


The MultiAsSingleDimMatrix class stores the 2D array as a 1D array. By doing this, the data can be communicated using the datatype of the array---in our example, the MPI.DOUBLE datatype.