Getting Started with Google Colab

What is Google Colab?

Google Colab (short for “Colaboratory”) is a free online tool that lets you write and run Python code in your web browser. Think of it like Google Docs, but for code!

Why we love it for beginners:

• ✅ No installation needed
• ✅ No setup required
• ✅ Pre-installed with common libraries
• ✅ Free GPU access (for fast computation)
• ✅ Easy sharing with others
• ✅ Automatic saving to Google Drive

Step 1: Open Your First Notebook

Click this link to open the first GenJAX notebook:

📓 Open: Chapter 2 - Your First GenJAX Model

Step 2: Make a Copy (So You Can Edit)

When the notebook opens, you’ll see a yellow banner that says “You are using Colab in playground mode.”

Click: “Copy to Drive” (top right, or in the banner)

This creates your own copy that you can edit and save!

Step 3: Understanding the Interface

Let me show you around:

The Notebook Structure

A Colab notebook has cells — little boxes that contain either:

• Text cells (like this explanation)
• Code cells (Python code you can run)

Running Code Cells

See a cell with code like this?

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print("Hello, Chibany!")

To run it:

1. Click on the cell
2. Press Shift + Enter (or click the ▶️ play button on the left)

Try it! You should see “Hello, Chibany!” appear below the cell.

Interactive Widgets

Throughout the notebooks, you’ll see sliders and controls that let you change values and instantly see updated results. We’ll use these to explore probability!

Step 4: Install GenJAX

The first code cell in each notebook will look like this:

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# Install GenJAX (this takes about 1-2 minutes the first time)
pip install genjax

What this does:

• In Colab notebooks, you use !pip install to run shell commands
• pip install means “download and install”
• genjax is the library we’re installing

To run it:

1. Click the cell
2. Press Shift + Enter
3. Wait for it to finish (you’ll see progress messages)

Step 5: Import Required Libraries

After installation, you’ll typically see a cell like:

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import jax
import jax.numpy as jnp
import genjax
from genjax import gen, bernoulli
import matplotlib.pyplot as plt

What this does:

• import means “load this library so we can use it”
• We’re loading JAX (for computation), GenJAX (for probability), and matplotlib (for plotting)

Just run it! You don’t need to understand every line. Think of it like turning on the lights before you start working.

Step 6: Your First Code!

Now you’re ready to run real GenJAX code! In the next chapter, you’ll:

• Write a generative function for Chibany’s meals
• Generate thousands of random days
• Visualize the results
• Use sliders to change probabilities and see what happens

Common Issues & Solutions

“Runtime disconnected”

Problem: Colab disconnects after ~90 minutes of inactivity Solution: Just reconnect and re-run the cells (start to finish)

“Restart Runtime” button

Problem: Something went wrong and you need a fresh start Solution: Click Runtime → Restart runtime → Re-run all cells

Code won’t run

Problem: Cells need to be run in order Solution: Click Runtime → Run all (to run from top to bottom)

Keyboard Shortcuts (Optional)

These can make you faster, but they’re optional:

Quick Reference Card

Save this for later:

Running Code:

1. Click cell
2. Shift + Enter

Saving Work:

• Auto-saves to Google Drive (if you copied to Drive)
• Manual save: File → Save

Fresh Start:

• Runtime → Restart runtime

Getting Help:

• In code cell, type ?function_name and run to see documentation
• Or just Google your question!

You’re Ready!

Now you have: ✅ Google Colab open ✅ Your own copy of the notebook ✅ GenJAX installed ✅ Basic understanding of the interface

Next steps:

• Chapter 1: Python Essentials → - Learn just enough Python
• Chapter 2: Your First GenJAX Model → - Jump right into coding!