# Development Environments

For this course, we will use the web-based development environment [Jupyterhub](https://en.wikipedia.org/wiki/Project_Jupyter). It is available to all participants for the duration of the course.

For long-term work, a personal installation is recommended.


## Installing on Your Own Computer (Linux/MacOS/MS Windows)

1. Install Julia with the installation and update manager **juliaup**:  <https://github.com/JuliaLang/juliaup/>.
2. Install **Visual Studio Code** as editor/IDE: <https://code.visualstudio.com/>.
3. Install the **Julia language extension** in VS Code: <https://www.julia-vscode.org/docs/stable/gettingstarted/>.

Getting started:

- Create a new file with the extension `.jl` in VS Code
- Write Julia code
- `Shift-Enter` or `Ctrl-Enter` at the end of a statement or block starts a Julia-REPL: the code is copied to the REPL and executed
- [Key bindings for VS Code](https://code.visualstudio.com/docs/getstarted/keybindings#_keyboard-shortcuts-reference)
and [for Julia in VS Code](https://www.julia-vscode.org/docs/stable/userguide/keybindings/)


### The Julia-REPL

When Julia is started directly from the command line, the [Julia-REPL](https://docs.julialang.org/en/v1/stdlib/REPL/) (*read-eval-print* loop) opens, allowing interactive work.


```default
$ julia
                _
    _       _ _(_)_     |  Documentation: https://docs.julialang.org
   (_)     | (_) (_)    |
    _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
   | | | | | | |/ _` |  |
   | | |_| | | | (_| |  |  Version 1.12.5 (2026-02-09)
  _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia>
```

## Working on the  [Jupyterhub Webserver](https://misun103.mathematik.uni-leipzig.de/)

### Jupyterhub & Jupyter

- [JupyterHub](https://de.wikipedia.org/wiki/Project_Jupyter) is a multi-user server for Jupyter notebooks.
- Jupyter is a web-based interactive programming environment 
- Originally written for and in Python, but now supports many programming languages
- In Jupyter, one works with so-called *notebooks*: structured text files (JSON) with the file extension `*.ipynb`.

Our Jupyterhub server: <https://misun103.mathematik.uni-leipzig.de/>

After logging into Jupyterhub, a file manager appears:

::: {.content-visible when-format="html"}
![](../images/notebook001.png)
:::

::: {.content-visible when-format="typst"}
![Jupyterhub file manager](../images/notebook001.png){width=50%}
:::


This can be used to:

- open existing *notebooks*,
- create new *notebooks*,
- upload files, e.g., notebooks, from your local computer,
- log out when finished (Please don't forget this!) 

### Jupyter notebooks


::: {.content-visible when-format="html"}
![](../images/notebook003.png)
:::

::: {.content-visible when-format="typst"}
![Jupyter Notebook](../images/notebook003.png){width=50%}
:::


*Notebooks* consist of cells. Cells can contain

- Code, or
- Text/documentation (Markdown)

In text cells, the markup language [Markdown](https://en.wikipedia.org/wiki/Markdown) can be used for formatting and LaTeX for mathematical equations.

::: {.callout-tip }
Please check the `User Interface Tour` and `Keyboard Shortcuts` topics in the `Help` menu!
:::

The cell currently being worked on can be in `command mode` or `edit mode`.

:::{.narrow}

|        | *Command mode* | *Edit mode* |
|:-------|:---------------:|:-----------:|
| Activate mode | `ESC`  | Double-click or `Enter` in cell |
| New cell | `b`    |  `Alt-Enter` |
| Delete cell | `dd` | |
| Save notebook | `s` | `Ctrl-s` |
| Rename notebook | `Menu -> File -> Rename` | `Menu -> File -> Rename` |
| Close notebook | `Menu -> File -> Close & Halt` | `Menu -> File -> Close & Halt` |
| *Run cell* | `Ctrl-Enter` | `Ctrl-Enter` |
| *Run cell, move to next cell* | `Shift-Enter` | `Shift-Enter` |
| *Run cell, insert new cell below* | `Alt-Enter` | `Alt-Enter` |

:  {.striped}

:::

::: {.content-visible when-format="html"}
![](../images/notebook002.png)
:::

::: {.content-visible when-format="typst"}
![Julia working...](../images/notebook002.png){width=50%}
:::


When a cell is working, its cell number becomes a `*` and
the `kernel busy` indicator appears (solid black dot at the top right next to the
Julia version). If this takes too long (an *infinite loop*
can easily happen):

- click `Menu -> Kernel -> Interrupt`. If this doesn't work,
- click `Menu -> Kernel -> Restart`.


::: {.callout-important }
After a `kernel restart`, all cells containing the required definitions,
`using` statements, etc. must be executed again.


**At the end of each session, please always:**

- `Menu -> File -> Save & Checkpoint`
- `Menu -> File -> Close & Halt`
- `Logout`
:::