# Installation

We've tried to make Skywalker as easy as possible to use with your current
software. To build it, you need

+ [CMake v3.10+](https://cmake.org/)
+ GNU Make
+ Reliable C and C++ compilers (like GCC and Clang)
+ A decent Fortran compiler (like GFortran or Intel's `ifort`)

You can also build Skywalker on Windows. It has been tested with Visual Studio
2022 Community Edition with the Intel oneAPI Fortran Classіc (`ifort`) compiler.
Your mileage may vary if you use different versions of Visual Studio or a
different Fortran compiler.

## Clone the Repository

First, go get the [source code](https://github.com/eagles-project/skywalker)
at GitHub:

=== "SSH"
    ```
    git clone git@github.com:eagles-project/skywalker.git
    ```
=== "HTTPS"
    ```
    git clone https://github.com/eagles-project/skywalker.git
    ```

This places a `skywalker` folder into your current path. If you're using
Visual Studio, just use your Git workflow to clone the repository.

## Configure Skywalker

Skywalker uses CMake as its build system. CMake accepts a few options that
specify how Skywalker should be built. Here are the most important options for
you to consider.

* `CMAKE_INSTALL_PREFIX` sets the path to which the Skywalker C, C++, and
  Fortran headers/module and libraries are installed. This is often something
  like `/usr/local` by default.
* `CMAKE_BUILD_TYPE` controls whether optimization is on (`Release`) or whether
  the build is instrumented for a debugger (`Debug`).
* `SKYWALKER_PRECISION` can be set to `single` or `double` (default) to control
  the precision of floating point numbers.
* `CMAKE_C_COMPILER` sets the C compiler that is used to build Skywalker.
  Usually, the default compiler is fine, but if you want to use an MPI-capable
  compiler or a specific vendor compiler, you can specify it with this option.
* `ENABLE_FORTRAN`, when set to `ON` (its default value), builds Fortran support
  for Skywalker. You can set this to `OFF` if you don't need Fortran.
* `CMAKE_Fortran_COMPILER` sets the Fortran compiler that is used to build
  Skywalker's Fortran interface.

=== "Linux/Mac"
    From the top-level `skywalker` directory, create a "build" directory
    (e.g. `build`). This is where you'll configure and build Skywalker. For example,
    to configure a debuggable build of Skywalker that uses double precision, do the
    following:

    ```
    mkdir build
    cd build
    cmake -DCMAKE_INSTALL_PREFIX=/path/to/install \
          -DCMAKE_BUILD_TYPE=Debug \
          -DSKYWALKER_PRECISION=double \
          ..
    ```

    This creates a set of `Makefile`s in your build directory. Now you're ready
    to build.

=== "Windows"
    Visual Studio gets its settings from `CMakeSettings.json` in the top-level
    source directory.

## Build, Test, and Install Skywalker

=== "Linux/Mac"
    To build skywalker, make sure you're in your build directory and type

    ```
    make -j
    ```

    If this process succeeds, you can run the tests and examples included with
    Skywalker by typing

    ```
    make test
    ```

    If you're using Linux, you can also run Skywalker's tests through
    [Valgrind](https://valgrind.org) to check for memory corruptions and leaks
    with

    ```
    make memcheck
    ```

    (but be prepared to wait a while for the tests to finish).

    You should see several tests run (and hopefully pass!). Now, to install
    Skywalker to the path you specified with `CMAKE_INSTALL_PREFIX`, type

    ```
    make install
    ```

=== "Windows"
    You should be able to use the Build and Test workflows in Visual Studio to
    build, test, and install Skywalker.

The installation process produces the following artifacts, which you can use to
build your own Skywalker programs:

* `PREFIX/lib/libskywalker_<precision>.a`, a library you can use with a C or C++
  Skywalker program.
* `PREFIX/include/skywalker.h`, a C header file that provides Skywalker's C
  interface.
* `PREFIX/include/skywalker.hpp`, a C++ header file that provides Skywalker's
  C++ interface.
* `PREFIX/share/skywalker.cmake`, a CMake file that includes installation
  information for Skywalker, plus a function called `add_skywalker_driver` you
  can use to build your own driver programs.

When `ENABLE_FORTRAN` is set to `ON`, you get additional Fortran artifacts:
* `PREFIX/lib/libskywalker_f90_<precision>.a`, a library you can use with a
  Fortran Skywalker program.
* `PREFIX/include/skywalker.mod`, a Fortran 90 module header file that provides
  Skywalker's Fortran interface.

On Windows, the library files have a `.lib` suffix instead of `.a`.

Here, `PREFIX` stands for the path you passed to `CMAKE_INSTALL_PREFIX`. These
files are all you need to build Skywalker programs.

## Try It Out!

At this point, you're ready to start using Skywalker. Look at the
[Quick Start](quick_start.md) section to get started.