  In this report we document performance test results on a SUNDIALS-based
multiphysics demonstration application. We aim to assess the large-scale
parallel performance of new capabilities that have been added to the SUNDIALS
suite of time integrators and nonlinear solvers in recent years under funding
from both the Exascale Computing Project (ECP) and the Scientific Discovery
through Advanced Scientific (SciDAC) program, specifically: (a) SUNDIALS' new
MPIManyVector module, that allows extreme flexibility in how a solution
"vector" is staged on computational resources, (b) ARKode's new multirate
integration module, MRIStep, allowing high-order accurate calculations that
subcycle "fast" processes within "slow" ones, (c) SUNDIALS' new flexible linear
solver interfaces, that allow streamlined specification of problem-specific
linear solvers, and (d) SUNDIALS' new N_Vector additions of "fused" vector
operations (to increase arithmetic intensity) and separation of reduction
operations into "local" and "global" versions (to reduce latency by combining
multiple reductions into a single MPI_Allreduce call). We anticipate that
subsequent reports will extend this work to investigate a variety of other new
features, including SUNDIALS' generic SUNNonlinearSolver interface and
accelerator-enabled N_Vector modules, and upcoming MRIStep extensions to
support custom "fast" integrators (that leverage problem structure) and IMEX
integration of the "slow" time scale (to add diffusion).
