On the efficient parallel computing of long term reliable trajectories for the Lorenz system.

In this work we propose an efficient parallelization of multiple-precision Taylor series method with variable stepsize and fixed order. For given level of accuracy the optimal variable stepsize determines higher order of the method than in the case of optimal fixed stepsize. Although the used order of the method is greater then that in the case of fixed stepsize, and hence the computational work per step is greater, the reduced number of steps gives less overall work. Also the greater order of the method is beneficial in the sense that it increases the parallel efficiency. As a model problem we use the paradigmatic Lorenz system. With 256 CPU cores in Nestum cluster, Sofia, Bulgaria, we succeed to obtain a correct reference solution in the rather long time interval - [0,11000]. To get this solution we performed two large computations: one computation with 4566 decimal digits of precision and 5240-th order method, and second computation for verification - with 4778 decimal digits of precision and 5490-th order method.