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%T Diffusion limited aggregation: An example of real\-time parallelisation
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%A  D. R. Morse,  A. M. Welch, Peter H. Welch
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%E  Hussein S. M. Zedan
%B OUG\-13: Real\-Time Systems with Transputers
%X The simulation of the growth of Diffusion\-Limited
   Aggregates (DLA) is representative of a class of
   \[rs]shared\[rs] data\-structure computations that does not
   yield to traditional parallelisation methods (such as
   \[rs]farming\[rs], \[rs]geometric decomposition\[rs] and
   \[rs]data\-flow\[rs]). The difficulty is that the shared
   data\-structure is large and evolving, the required access
   to it from each processor is random and very high, and the
   computation per access is very low. These conditions also
   make these problems most unsuitable for shared\-memory
   parallel computers.This paper presents a parallelisation
   technique that does give linear speed\-up for this problem
   (at least, for up to 32 transputers). The
   cost\-effectiveness of the solution compares favourably with
   those published that use vector\-processing machines.The
   success of the parallelisation depends on real\-time issues
   associated with keeping each worker transputer sufficiently
   up\-to\-date with all its colleagues. Some
   \[rs]quasi\-relativistic\[rs] effects need to be taken into
   account as well!The speed\-ups achieved through this
   parallelisation are used to investigate the effect of
   various parameters (such as stride length and background
   drift) on the kind of DLA growth that is obtained. These
   studies would not be practical without the savings in time
   that have been realised from a parallel implementation of
   the DLA simulation.Finally, we characterise the features of
   those applications for which this parallelisation method is
   relevant.