Lecture II - First Steps in Julia

Applied Optimization with Julia

Dr. Tobias Vlćek

University of Hamburg

Technical Setup

Goals for Today

After this lecture, you will have:

A working Julia and Zed setup on your computer
Made your first Git commit
Learned how to submit assignments and earn bonus points
Started with the first tutorials

Download and Install Julia

To prepare for the upcoming lectures, we start by installing the Julia Programming Language and an Integrated Development Environment (IDE) to work with Julia.

Installing Julia

Head to julialang.org and follow the instructions.
The easiest way to install Julia is via the shell/terminal
Later, you can then manage Julia with juliaup

If you are ever asked to add something to your “PATH”, do so!

Zed

Next, we are going to install Zed, the editor of this course
macOS: brew install --cask zed (or the installer from zed.dev)
Windows: installer from zed.dev/windows
Linux: curl -f https://zed.dev/install.sh | sh

On Windows, Zed needs a DirectX-11-capable GPU. If it only shows a blank window, use VS Code with the “Julia (Julia Language Support)” extension instead: everything in this course works there too.

Verify the Installation

Start Zed and take a look around
Open the command palette: Ctrl+Shift+P (Windows/Linux) or Cmd+Shift+P (macOS)
Choose zed: extensions and search for “Julia”
Install the Julia extension for syntax support

Create a New File

Create a new file with a “.jl” ending
Save it somewhere on your computer
e.g., in a folder that you will use in the course

println("Hello World!")

Hello World!

Run the File

Open a terminal in the folder where you saved the file
Run it with julia test.jl
Later, we will run files cell by cell directly from Zed — the first tutorial sets that up

Everything Working?

If the terminal prints Hello World! → perfect!
If not, the terminal likely cannot find the path to Julia
Close and reopen the terminal after installing Julia, and say yes to any “PATH” question during installation
Then try to run the file again

Don’t worry if it is not running right away. We will fix this together!

Learning Julia

Julia as a Language

The following three lectures are dedicated to learning the basics
Start with the very basics and gradually move on
Focus in the first two lectures on the programming language
Third lecture dedicated to Mathematical Optimization

A First Taste of Julia

Question: What will your savings be worth in 10 years?

savings = 1000       # Euros in your account
interest_rate = 0.03 # 3% interest per year
value = savings * (1 + interest_rate)^10
println("Value after 10 years: ", round(value; digits=2))

Value after 10 years: 1343.92

Don’t worry if this looks new — you will be able to read and write code like this after the tutorials!

Your Turn

Julia in Zed

Tutorials in Zed

The easiest way to work on the tutorials is a .jl file in Zed, run cell by cell
For detailed instructions, just open the first tutorial
It explains step-by-step how to set up the course environment and run the cells

If you use .jl files, you can also put them under version control with Git, as you will see later in this lecture.

Downloading the Tutorials

You will find the tutorial files next to the tutorial pages
On each page, you will find a button Julia on the right
Click it to download the .jl file and save it
The file is split into cells by # %% markers, ready to run cell by cell
I’d really recommend storing the files in a separate directory for this course

Learning by Doing

The best way to learn a programming language is by doing
We will therefore solve problems the coming weeks
The goal is to get you familiar with the language
You can discuss the problems with your fellow students
You can hand in your solutions to receive bonus points!

Working with Git

What is Git?

Git is a version control system that tracks changes in your code
Helps you collaborate and keep track of your work
Saves “snapshots” of your project at different stages
You can always go back to previous versions if something goes wrong
No need to create files like tutorial_v1.jl and tutorial_v2.jl

Installing Git

Head to git-scm.com and download Git
Follow the installation instructions on the website for your OS

If you have any questions, feel free to ask!

Git in Zed

Zed has built-in Git support!
Open the Git panel with the Git icon in the status bar
Staging, committing and file history need no extension

Git is not required for the course, but strongly recommended: once you get used to it, it becomes invaluable, especially if you are working with a lot of code!

Initialize a Repository

Open your project folder (of our lecture) in Zed
Open the Git panel and initialize a repository
Or run git init in a terminal in that folder
Your folder is now a Git repository!

You can also synchronize your repository with GitHub or other hosting services. Then, your code is saved in a remote location, making it accessible from anywhere and allowing collaboration with others.

Making Your First Commit

Make changes to your files (e.g., work on a tutorial .jl file)
Open the Git panel
You’ll see your changed files listed there
Tick the checkbox next to files to stage them
Add a commit message describing your changes
Press Cmd+Enter (macOS) or Ctrl+Enter to commit

Viewing History

Right-click a file and open its File History
See every commit that changed this file
Select a commit to see what changed in it

Start using Git from day one! Even for small projects, it’s a good habit to develop.

Assignments

Find Your Group

You hand in the assignments as a group of up to three
Take a few minutes now: who do you want to work with?
Tell me your group today and I will set it up in Moodle
Your group stays the same for the whole semester

You would rather work alone? That is fine too: you are then a group of one.

Submission of Assignments

Submit the assignment via Moodle: one upload counts for your group
Upload the tutorial .jl files and keep their file names
The assignment is due at the start of the next tutorial
After that, Moodle does not accept uploads anymore

Don’t forget to save your files before uploading them to Moodle!

Grading of Assignments

Each assignment gives up to 5 points in Moodle
Divided by 10, that is up to 0.5 bonus points for the exam
You can get a maximum of 6.0 bonus points from the assignments
You need to pass the exam first, to receive any bonus points!

The assignments are not mandatory, but highly recommended!

What About AI?

You may use AI tools: say so in one line in your submission
But the bonus points only count if you pass the exam
And in the exam, there is no AI to help you
So it pays off to solve the tutorials yourself

The full rules are in the AI policy on the course website.

Five Tutorials

Topics of the Tutorials

Variables: Learn how to assign values to variables
Vectors: Learn how to create and manipulate vectors
Comparisons: Learn how to compare values
Loops: Learn how to use loops to repeat code
Dictionaries: Learn how to store and look up key-value pairs

Dictionaries will become important later: they are how we will store and look up the data of our optimization models.

Get Started with the Tutorials

Download the first tutorial file and open it
Start with the first problem and solve it step by step
You can find the tutorials here on the website
You can ask questions anytime!

And that’s it for this lecture!

The remaining time we will already start working on the first problems.

Literature

Lauwens, B., & Downey, A. B. (2019). Think Julia: How to think like a computer scientist (First edition). O’Reilly®. Link to the free book website.
Julia Documentation

For more interesting literature to learn more about Julia, take a look at the literature list of this course.