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nihiL7331 merged 2 commits into from
Aug 9, 2026
Merged

docs: add Configuration section and update the License section (MIT->Zlib) #36

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docs: add `Configuration` section
nihiL7331 Aug 9, 2026
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docs: update `License` section
nihiL7331 Aug 9, 2026
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23 changes: 14 additions & 9 deletions README.md
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Expand Up @@ -9,15 +9,8 @@
## Quickstart

Include the header in one C file with `POLESITTER_IMPLEMENTATION` defined. \
Define `PS_MULTITHREADING` as well when using more than one thread. \
Define `PS_2D` when simulating in two-dimensional space.
Use #define PS_ORDER 1-3 to pick maximum order of Taylor expansions used in solver. \
* (higher = worse performance, better accuracy)
* (default = 2)


```c
#define PS_MULTITHREADING
#define POLESITTER_IMPLEMENTATION
#include "polesitter.h"
```
Expand Down Expand Up @@ -124,6 +117,18 @@ int main(void) {
}
```

### Configuration

Define these before `#include "polesitter.h"` to configure the solver:

| Macro | Description |
| --- | --- |
| `PS_2D` | Compiles the solver for 2D (quadtree-based) instead of 3D (octree-based). |
| `PS_ORDER <N>` | Sets the Taylor expansion order (1=Dipole, 2=Quadrupole, 3=Octupole). |
| `PS_MULTITHREADING` | Enables the parallel implementation. |
| `PS_USE_AVX2` | Explicitly enables AVX2 intrinsics for x86 CPUs. |
| `PS_USE_NEON` | Explicitly enables NEON intrinsics for ARM CPUs. |

## Pipeline

The most common N-body tree codes rely on the Barnes-Hut algorithm, ending up with O(N log N) time complexity.
Expand All @@ -139,7 +144,7 @@ It calculates interactions between cells and treats distant forces as a local ba
The solver executes physics ticks in four distinct passes over the Z-ordered octree:

1. **Upward pass (P2M & M2M)**
- **Particle-to-Multipole:** Leaf nodes calculate their initial multipole expansion (total mass and cneter of mass) from their particles.
- **Particle-to-Multipole:** Leaf nodes calculate their initial multipole expansion (total mass and center of mass) from their particles.
- **Multipole-to-Multipole:** These expansions are aggregated up the tree from the leaves to the root. Every node now represents the center of mass of all its children.

2. **Interaction pass (M2L)**
Expand All @@ -159,7 +164,7 @@ The solver executes physics ticks in four distinct passes over the Z-ordered oct

## License

MIT License.
Zlib license.

## Sources

Expand Down