# Lecture 5 Part 2: Forward Automatic Differentiation via Dual Numbers | Summary and Q&A

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December 1, 2023
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MIT OpenCourseWare
Lecture 5 Part 2: Forward Automatic Differentiation via Dual Numbers

## TL;DR

Automatic differentiation is a powerful technique in computer science that allows computers to calculate derivatives of functions, making use of fundamental rules of calculus and simple code implementation.

## Key Insights

• 💻 Automatic differentiation combines mathematics and computer science to efficiently calculate derivatives.
• 🎭 It relies on providing basic rules of mathematical operations to computers, which then perform derivative calculations simultaneously.
• 🫚 The Babylonian square root algorithm serves as an example of automatic differentiation applied to a simple computation.
• 🪡 Automatic differentiation eliminates the need for symbolic derivation and offers more accuracy than numerical difference methods.

## Transcript

[SQUEAKING] [RUSTLING] [CLICKING] OK. So just to let you know what this notebook is and isn't, this notebook is kind of meant to let you see how automatic differentiation is kind of magical in a way. That's kind of the real purpose. You'll start to get a bit of a feel for how forward mode works. And what I'd like to emphasize is to what extent this... Read More

### Q: How does automatic differentiation differ from symbolic differentiation?

Automatic differentiation is not symbolic; it relies on algorithmic implementation using fundamental calculus rules. It allows computers to compute derivatives accurately without explicitly representing the equation in symbolic form.

### Q: What is the significance of the Babylonian square root algorithm in demonstrating automatic differentiation?

The Babylonian square root algorithm serves as a simple example to showcase how automatic differentiation works. By applying the algorithm to functions, it is possible to calculate derivatives accurately without resorting to symbolic or numerical methods.

### Q: How does automatic differentiation handle the calculation of derivatives in computer programs?

Automatic differentiation relies on providing the basic rules of mathematical operations like addition, subtraction, multiplication, and division. These rules are implemented in computer code in such a way that the derivative calculations are performed simultaneously with the original computations.

### Q: What advantages does automatic differentiation provide over traditional symbolic or numerical methods?

Automatic differentiation eliminates the need for symbolic derivation, which can be complex and prone to human errors. It also overcomes the limitations of numerical difference methods, such as choosing appropriate delta values, by accurately calculating derivatives without numerical approximations.

## Summary & Key Takeaways

• The notebook aims to showcase the magic of automatic differentiation and highlight its role in both computer science and mathematics.

• Automatic differentiation is not symbolic like Mathematica or Wolfram Alpha, nor is it numerical difference methods like forward or backward derivatives. It is a combination of mathematical principles and algorithmic implementations.

• The Babylonian square root algorithm is used as an example to demonstrate how automatic differentiation can be used to calculate derivatives accurately without symbolic or numerical methods.