# An Optimized Linked-Cell NNPS Algorithm in Meshless CFD Methods

**Repository Path**: zoziha/nnps

## Basic Information

- **Project Name**: An Optimized Linked-Cell NNPS Algorithm in Meshless CFD Methods
- **Description**: 模块化+面向对象设计，用于SPH、MPS等CFD粒子方法的近邻粒子搜索
- **Primary Language**: FORTRAN
- **License**: MIT
- **Default Branch**: main
- **Homepage**: https://nnps.netlify.app/
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 0
- **Created**: 2022-03-10
- **Last Updated**: 2025-08-11

## Categories & Tags

**Categories**: Uncategorized

**Tags**: nnps, cfd, sph

## README

<div align='center'>

# NNPS for Particle Simulation

![NNPS](https://img.shields.io/badge/NNPS-v1.5.2409-blueviolet)
![Language](https://img.shields.io/badge/-Fortran-734f96?logo=fortran&logoColor=white)
![license](https://img.shields.io/badge/License-MIT-pink)

</div>

Nearest Neighbor Particle Search (NNPS) scheme practice for particle simulation, coded in Modern Fortran.

## Build

Only GFortran compiler and meson-build is supported.

```sh
meson setup build
meson compile -C build
```

Build the documentation with `doxygen`:

```sh
doxygen ./doc/doxyfile
start ./build/Doxygen/html/index.html  # Open the HTML file with browser in Windows
```

## Example

```sh
./build/example_grid2d.exe
```

```fortran
program example_grid2d

    use nnps_module, only: nnps_grid2d, wp
    use display_module, only: display
    implicit none

    type(nnps_grid2d) :: nnps
    real(wp), dimension(2, 4) :: loc = reshape([0.0_wp, 1.0_wp, 2.0_wp, 1.5_wp, &
                                                1.0_wp, 1.0_wp, 0.5_wp, 1.0_wp], [2, 4])
    integer, pointer :: pairs(:)
    real(wp), pointer :: rdxs(:)

    call nnps%init(loc, n=4)
    call nnps%query(0.6_wp, pairs, rdxs, n=4)

    print *, '*** grid find (2D)'
    call display(pairs, 'pairs index:', brief=.false.)
    call display(loc(:, pairs), 'pairs coordinates:', brief=.false.)
    call display(rdxs, 'rdxs:', brief=.false.)

end program example_grid2d
!  *** grid find (2D)
! [vector_type: 4] pairs index:
! 3, 4, 4, 1
! [matrix: 2*4] pairs coordinates:
!  1.000E+00,  5.000E-01,  5.000E-01,  0.000E+00;
!  1.000E+00,  1.000E+00,  1.000E+00,  1.000E+00
! [vector_type: 6] rdxs:
!  5.000E-01,  5.000E-01,  0.000E+00,  5.000E-01,  5.000E-01,  0.000E+00
```

## Benchmark

There are some benchmarks in the `test` folder. Set `OMP_NUM_THREADS` environment variable to control the number of threads.

```sh
export OMP_NUM_THREADS=4
./build/bench2dn-grid.exe 10000 1.0  # choose 10k particles and loading_factor = 1.0 for benchmark program
```

## Links

+ [wikipedia/Quadtree](https://en.wikipedia.org/wiki/Quadtree)
+ [lewisfish/quad-tree](https://github.com/lewisfish/quad-trees)
+ [bilibili/Dejavu32/[Coding Challenge ]:四叉树的实现 以及 碰撞检测应用（Quadtree Collisions )](https://www.bilibili.com/video/BV1ub411S7N5?spm_id_from=333.999.0.0)
+ [CodingTrain/QuadTree](https://github.com/CodingTrain/QuadTree)