Fast dynamo action in spherical geometry: Numerical calculations using parallel virtual machines

I present a numerical code designed to solve the magnetic induction equation in spherical geometry. I demonstrate how to use the message‐passing software package parallel virtual machine to distribute this code over a cluster of workstations, and consider how the parallel efficiency depends upon the ratio of communication to computation. I demonstrate that by estimating these quantities in advance, one can very accurately predict the parallel efficiency that will result when the code is distributed over a cluster of given communication and computation speeds. It is suggested that such estimates would be extremely useful in deciding in advance whether or not it would be worthwhile to implement distributed versions of other codes. © 1995 American Institute of Physics.