NEXT - Newtonian EXact Trajectories

Multi-Threaded & Distributed Simulation Tool for Solving the N-Body Problem

Powered by Barnes-Hut Octree O(N log N), Symplectic KDK Leapfrog Integration, OpenMP, and MPI.

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Key Features

• O(N log N) Barnes-Hut Octree: Scalable spatial tree hierarchy with multipole expansions.
• Symplectic KDK Leapfrog Integrator: Preserves energy stability over extended numerical integration.
• Division-Avoiding Algebra: Optimized force calculations (3–6x speedup by minimizing costly float divisions).
• Hybrid Parallelism: OpenMP multi-threading (multi-core) + MPI (distributed computing cluster).
• Precision Modes: Configurable compile-time switching between FP32 and FP64.
• Multi-Format Output: Native support for VTK, VTU (ParaView), and HDF5.
• Python IC Builder: Legacy initial condition scripts (tools/icbuilder.py).

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Building NEXT

# Configure build directory
cmake -B build -S .

# Build executable (Release configuration)
cmake --build build --config Release

For detailed platform-specific installation instructions, see:

• Windows (MSVC)
• Windows (MinGW / MSYS2)
• Linux (Ubuntu / Debian / Fedora)
• macOS

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CLI Usage & Demo

# Generate initial conditions
cd examples/TwoBodies
python two_body.py

# Run NEXT simulation
../../next two_body.txt <threads> <dt> <dump_interval> <vtk|vtu|hdf5> [max_steps]

# Example: Run 8 threads, dt=0.001, dump every 0.1s, output VTU, for 100 max steps
../../next two_body.txt 8 0.001 0.1 vtu 100

Command Arguments Explained:

1. input.txt - Path to initial condition particle file
2. threads - Number of CPU threads (OpenMP)
3. dt - Baseline time step
4. dump_interval - Simulation time interval between output dumps
5. format - Output format (vtk, vtu, or hdf5)
6. [max_steps] - (Optional) Maximum simulation steps before auto-exit

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Media & Previews

• Preview the figure-eight simulation