Akaroa II Version 2.4.2 User's Manual

TR-COSC 07/97Akaroa takes a different approach to parallel simulation, that of multiple replications in parallel or MRIP [1-5]. Instead of dividing up the simulation program, multiple instances of an ordinary serial simulation program are run simultaneously on different processors. These instances run independently of one another, and continuously send back to a central controlling process observations of the simulation model parameterswhich are of interest. The central process calculates from these observations an overall estimate of the mean value of each parameter. When it judges that it has enough observations to form an estimate of the required accuracy, it halts the simulation. Since the simulations run independently, if there are n copies of the simulation running on n processors they will on average produce observations at n times the rate of a single copy, and therefor produce enough observations to halt the simulation after 1/nth of the time. So theMRIP technique can be expected to speed up the simulation approximately in proportion to the number of processors used. MRIP also provides a degree of fault tolerance. It doesn’t matter which instance of the simulation the estimates come from, so if one processor fails, the program itwas running can be restarted and the simulation continued without penalty. Alternatively, the simulation can simply be continued with one less processor and take proportionately longer to complete. In summary, the advantages of the MRIP technique are that it can be applied to any simulation program without the need to parallelise it or modify it in any way; it provides a speedup proportional to the number of processors; and it improves the reliability of the simulation