# otswap

```{include} ../README.md
:start-after: <!-- docs:about-start -->
:end-before: <!-- docs:about-end -->
```

The two APIs are one library: the C++ library and the Python package run the
same code and give the same results, bit for bit. [Names side by
side](naming.md) maps one to the other, and the [guide](guide.md) covers what
applies to both.

## Install

```
pip install otswap
```

For the C++ library, build and install it with CMake; it needs a C++17
compiler and cfitsio, uses OpenMP when found, and fetches meshsearch when it is
not installed:

```
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build
cmake --install build --prefix /path/to/prefix
```

and use it from your own CMake project:

```cmake
find_package(otswap 0.1 CONFIG REQUIRED)
target_link_libraries(your_target PRIVATE otswap::otswap)
```

## In a few lines

A box reconstruction of tracers given as an array, its mean displacement, and
a file with one row per tracer:

::::{tab-set}
:sync-group: lang

:::{tab-item} Python
:sync: python

```python
import otswap

result = otswap.reconstruct_box(tracers, n_realizations=8, seed=12345)
print(result.mean_displacement[0])
otswap.io.write_displacements("displacements.dat", result)
```
:::

:::{tab-item} C++
:sync: cpp

```cpp
#include "otswap/OT.h"

otswap::Config config;
config.nRealizations = 8;
config.seed = 12345;

otswap::Result result = otswap::reconstructBox(tracers, {}, config);
std::cout << result.meanDisplacement[0] << '\n';
otswap::io::writeDisplacements("displacements.dat", result);
```
:::

::::

`tracers` is an array of shape (N, 3) in Python, a `std::vector<double>` of
`3 * N` entries in C++, in Mpc/h. Without randoms, otswap draws them in the
tracers' bounding box. The [examples](examples.md) read real catalogues and
show every step.

```{toctree}
:maxdepth: 2
:hidden:

guide
method
examples
formats
cpp
python
naming
changelog
citing
```