pyxtensor 0.0.3

# pyxtensor

<!-- MarkdownTOC -->

- [Introduction](#introduction)
- [Usage](#usage)
- [Compile project using `setup.py`](#compile-project-using-setuppy)
- [Develop](#develop)

<!-- /MarkdownTOC -->

## Introduction

This library provides details for [pybind11](https://github.com/pybind/pybind11) such that an interface to NumPy arrays is automatically provided when including a function that takes any of the [xtensor](https://github.com/QuantStack/xtensor) classes as (return) argument(s).

> The behaviour is distinctly different from [xtensor-python](https://github.com/QuantStack/xtensor-python). The latter 'maps' NumPy arrays to a so-called `xt::pyarray` giving direct memory access to it. In contrast, [pyxtensor](https://github.com/tdegeus/pyxtensor) copies the NumPy object to a `xt::array` or `xt::tensor` and vice versa. This results in a simpler usage in which a C++ library can be exposed without any wrapper functions, however, with the disadvantage of using copies (that cost time, and that disallow in-place modifications).

## Usage

Consider the following example:

```cpp
#include <xtensor/xarray.hpp>
#include <pyxtensor/pyxtensor.hpp>

xt::xarray<double> timesTwo(const xt::xarray<double>& a)
{
return 2. * a;
}

namespace py = pybind11;

PYBIND11_MODULE(example, m)
{
m.def("timesTwo", &timesTwo);
}
```

As observed the [pybind11](https://github.com/pybind/pybind11) wrapper immediately acts on the [xtensor](https://github.com/QuantStack/xtensor) objects. See [pybind11_examples](https://github.com/tdegeus/pybind11_examples) for compilation strategies.

## Compile project using `setup.py`

In addition a Python module is provided to aid compilation using a `setup.py`. Both headers and the Python module can be installed using

```bash
pip install pyxtensor
```

Using the [pyxtensor](https://github.com/tdegeus/pyxtensor) Python module the `setup.py` of a [pybind11](https://github.com/pybind/pybind11) project can be as follows

```python
from setuptools import setup, Extension

import sys, re
import setuptools
import pybind11
import pyxtensor

ext_modules = [
Extension(
'ModuleName',
['path/to/pybind11/interface.cpp'],
include_dirs=[
pybind11 .get_include(False),
pybind11 .get_include(True ),
pyxtensor.get_include(False),
pyxtensor.get_include(True ),
pyxtensor.find_xtensor(),
pyxtensor.find_xtl(),
pyxtensor.find_eigen(),
],
language='c++'
),
]

setup(
name = 'ModuleName',
description = 'Short description',
long_description = 'Long description',
version = 'v0.1.2',
license = 'MIT',
author = 'Tom de Geus',
author_email = '...',
url = 'https://github.com/...',
ext_modules = ext_modules,
install_requires = ['pybind11>=2.2.0','pyxtensor>=0.0.1'],
cmdclass = {'build_ext': pyxtensor.BuildExt},
zip_safe = False,
)
```

Compilation can then proceed using

```bash
python setup.py build
python setup.py install
```

## Develop

1. Update the version number as follows in `include/pyxtensor/pyxtensor.hpp``.

2. Upload the changes to GitHub and create a new release there (with the correct version number).

3. Upload the package to PyPi:

```bash
python setup.py bdist_wheel --universal
twine upload dist/*
```