Introduction

Here is a simple NBody simulator. It uses a naive algorithm - in a O(n²) complexity. The aim of this project is to have a first look at the Kokkos library.

From the Kokkos github repo :

The Kokkos C++ Performance Portability Ecosystem is a production level solution for writing modern C++ applications in a hardware agnostic way. Thanks to Kokkos, you can compile this code for multiple backends like OpenMP, CUDA, HIP.

Disclaimer: Please note that this project is a work in progress and may contain errors or programming oversights due to its experimental nature. Your understanding and feedback are appreciated as we continue to develop and refine this code.

Prerequisites

The code use Kokkos as a performance portability library. Then, you must have it to compile the project. I suggest you to install it and read the documentation for further understanding.

Compilation

Compile the code by specifying your kokkos install directory with the following commands :

cmake -B build -S . -DKokkos_ROOT=/usr/local/lib64/cmake/Kokkos
cmake --build build/

I Suggest you to read the Kokkos documentation if you want to compile with a specific backend.

Usage

You can currently launch the SOA version named NBody_SOA with :

./build/NBody_3D -N 10240 -nrepeat 100 -f 100 -d 0.001

With the following arguments :

• -n particles
• -nrepeat iterations
• d timestep
• f frames - each frame consume nrepeat iterations and save the values in the frames directory

Todo

To-Do List

• Refactoring
• Hierarchical parallelism with Kokkos
• Shared memory kernels with scratch pads
• Kokkos::SIMD usage
• Barnes-Hut implementation
• Fast Multipole Method (FMM) implementation
• Add periodic boundary conditions
• Python animation generator
• Set up the CMake build system
• Test the code on different backends (CUDA, OpenMP, Serial)