1. Installation Quick Start

Using Feel++ inside Docker is the recommended and fastest way to use Feel++.

We strongly encourage you to follow the install/containers.adoc#_docker if you begin with Feel++ in particular as an end-user.

2. Usage Quick Start

Start the main Feel++ Docker container feelpp/feelpp-toolboxes` as follows

Command line to start the docker container
``$docker run -it --rm -e LOCAL_USER_ID=`id -u$USER`  -v $HOME/feel:/feel feelpp/feelpp-toolboxes``  simply copy-paste the command line in your terminal to start the `feelpp/feelpp-toolboxes` container. Here are some explanations about the different parts in the command line ``````$ docker (1)
run (2)
-it (3)
--rm (4)
-e LOCAL_USER_ID=`id -u`(5)
-v $HOME/feel:/feel (6) feelpp/feelpp-toolboxes (7)``````  1 `docker` is the application that allows to create and execute Containers 2 `run` allows to execute the image `feelpp/feelpp-toolboxes` 3 the option `-it` runs Docker in interactive mode; 4 the option `--rm` makes sure that the container is deleted after the user exits Docker 5 we need to pass your user id to Docker so that the data you generate from Docker belongs to you; 6 maps the directory `$HOME/feel` on your host to `/feel` in Docker, Feel++ write in `/feel` the results of the simulations. Passing your id, i.e `LOCAL_USER_ID`, allows to ensure that the generated data on Feel++ belongs to you on your host system; 7 execute the image `feelpp/feelpp-toolboxes` and create the associated container .
 Several testcases (configuration files) have been installed in `/feel/testcases` (in Docker container) or `$HOME/feel/testcases` once you have executed the command line above. Running the quickstart Laplacian in sequential ``$ feelpp_qs_laplacian_2d --config-file /feel/testcases/quickstart/laplacian/feelpp2d/feelpp2d.cfg``
Explanations about running the quickstart Laplacian in sequential
``````> feelpp_qs_laplacian_2d (1)
--config-file /feel/testcases/quickstart/laplacian/feelpp2d/feelpp2d.cfg(2)``````
 1 executable to run 2 configuration file (text) to setup the problem : mesh, material properties and boundary conditions

The results are stored in Docker in

`/feel/qs_laplacian/feelpp2d/np_1/exports/ensightgold/qs_laplacian/`

`\$HOME/feel/qs_laplacian/feelpp2d/np_1/exports/ensightgold/qs_laplacian/`

The mesh and solutions can be visualized using e.g. Paraview or Visit.

 ParaView (recommended) is an open-source, multi-platform data analysis and visualization application. Visit is a distributed, parallel visualization and graphical analysis tool for data defined on two- and three-dimensional (2D and 3D) meshes
Quickstart Laplacian on 4 cores in parallel
``> mpirun -np 4 feelpp_qs_laplacian_2d --config-file /feel/testcases/quickstart/laplacian/feelpp2d/feelpp2d.cfg``

The results are stored in a simular place as above: just replace `np_1` by `np_4` in the paths above. The results should look like

 Solution Mesh

3. Syntax Start

Here are some excerpts from Quickstart Laplacian that solves the Laplacian problem. It shows some of the features of Feel++ and in particular the domain specific language for Galerkin methods.

First we load the mesh, define the function space define some expressions