Cross-Reference Simulation by Code-To-Code Adapter (CoToCoA) Library for the Study of Multi-Scale Physics in Planetary Magnetospheres

We have developed a cross-reference simulation code by a newly developed Code-To-Code Adapter (CoToCoA) library for the study of wave-particle interactions in planetary magnetospheres. The cross-reference simulation is a simulation model combining multiple simulation codes, which enables us to carry out multi-scale and multi-physics simulations. The cross-reference simulation is a unique approach in the space physics community, because HPC application codes are individually developed using a different set of basic equations and therefore the data transfer between the codes usually requires considerable efforts in adjusting interface. While the difficulties in combining the codes resulted in rare trials in the space physics community, the CoToCoA library plays crucial role in the modernization of the cross-reference simulation. The design concept of the CoToCoA library is to realize the communication among the codes with keeping necessary modification of the original code small, which enables us to carry out 'strong' cross-reference simulations; the data exchange among simulation codes is conducted by direct memory access, instead of file output as has been used in conventional 'weak' cross-reference simulations. In this paper, we present examples of the cross-reference simulation and describe how we implemented the CoToCoA library into the codes. We carry out a benchmark using a cross-reference simulation code and demonstrate that we can realize the 'strong' cross-reference simulation without incurring appreciable overheads as we used in the conventional 'weak' cross-reference simulations.