Tivadar Danka Profile picture
Jun 21, 2021 8 tweets 3 min read Read on X
What you see below is a cube in four dimensions.

Because humans can't see in more than 3D, it is challenging to make sense of it for the first time. However, there is a simple yet beautiful pattern behind.

This is how the magic is done!
What is a cube in one dimension?

It is simply two vertices connected with a line of unit length.
To move beyond and construct a cube in two dimensions, also known as a square, we simply copy a one-dimensional cube and connect each original vertex with its copy.

(These new edges are colored blue.)
You can probably guess the pattern by now.

Copying a cube's graph and connecting each of its vertices with its corresponding copy brings it to the next dimension.

This is how it looks in 3D.
Repeating this process one more time, we obtain a tesseract, that is, a cube in four dimensions.

(I stretched the new edges a bit to make it easier to see the pattern.)
All 8 of its faces are 3D cubes.
I have always found this pattern quite beautiful.

Geometry intrigued me since I was a child, and when I discovered how to draw a tesseract, I was over the moon.

Small things such as this ignited my desire to be a mathematician, and I still enjoy playing around with fun math.
I regularly post deep dive threads about mathematics and machine learning, explaining (seemingly) complex concepts in a simple way.

If you also love to look beyond the surface and understand how things work, consider giving me a follow!

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More from @TivadarDanka

Jul 1
The single most undervalued fact of linear algebra: matrices are graphs, and graphs are matrices.

Encoding matrices as graphs is a cheat code, making complex behavior simple to study.

Let me show you how! Image
If you looked at the example above, you probably figured out the rule.

Each row is a node, and each element represents a directed and weighted edge. Edges of zero elements are omitted.

The element in the 𝑖-th row and 𝑗-th column corresponds to an edge going from 𝑖 to 𝑗.
To unwrap the definition a bit, let's check the first row, which corresponds to the edges outgoing from the first node. Image
Read 18 tweets
Jun 30
In calculus, going from a single variable to millions of variables is hard.

Understanding the three main types of functions helps make sense of multivariable calculus.

Surprisingly, they share a deep connection. Let's see why! Image
In general, a function assigns elements of one set to another.

This is too abstract for most engineering applications. Let's zoom in a little! Image
As our measurements are often real numbers, we prefer functions that operate on real vectors or scalars.

There are three categories:

1. vector-scalar,
2. vector-vector,
3. and scalar-vector. Image
Read 16 tweets
Jun 30
Neural networks are stunningly powerful.

This is old news: deep learning is state-of-the-art in many fields, like computer vision and natural language processing. (But not everywhere.)

Why are neural networks so effective? I'll explain. Image
First, let's formulate the classical supervised learning task!

Suppose that we have a dataset D, where xₖ is a data point and yₖ is the ground truth. Image
The task is simply to find a function g(x) for which

• g(xₖ) is approximately yₖ,
• and g(x) is computationally feasible.

To achieve this, we fix a parametrized family of functions. For instance, linear regression uses this function family: Image
Read 19 tweets
Jun 28
One major reason why mathematics is considered difficult: proofs.

Reading and writing proofs are hard, but you cannot get away without them. The best way to learn is to do.

So, let's deconstruct the proof of the most famous mathematical result: the Pythagorean theorem. Image
Here it is in its full glory.

Theorem. (The Pythagorean theorem.) Let ABC be a right triangle, let a and b be the length of its two legs, and let c be the length of its hypotenuse.

Then a² + b² = c². Image
Now, the proof. Mathematical proofs often feel like pulling a rabbit out of a hat. I’ll go a bit overboard and start by pulling out two rabbits.

The first rabbit. Take a look at the following picture.

The depicted square’s side is a + b long, so its area is (a + b)². Image
Read 19 tweets
Jun 26
Problem-solving is at least 50% of every job in tech and science.

Mastering problem-solving will make your technical skill level shoot up like a hockey stick. Yet, we are rarely taught how to do so.

Here are my favorite techniques that'll loosen even the most complex knots: Image
0. Is the problem solved yet?

The simplest way to solve a problem is to look for the solution elsewhere. This is not cheating; this is pragmatism. (Except if it is a practice problem. Then, it is cheating.)
When your objective is to move fast, this should be the first thing you attempt.

This is the reason why Stack Overflow (and its likes) are the best friends of every programmer.
Read 18 tweets
Jun 25
What you see below is one of the most beautiful formulas in mathematics.

A single equation, establishing a relation between 𝑒, π, the imaginary number, and 1. It is mind-blowing.

This is what's behind the sorcery: Image
First, let's go back to square one: differentiation.

The derivative of a function at a given point describes the slope of its tangent plane. Image
By definition, the derivative is the limit of difference quotients: slopes of line segments that get closer and closer to the tangent.

These quantities are called "difference quotients". Image
Read 20 tweets

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