Tivadar Danka Profile picture
May 11, 2021 โ€ข 9 tweets โ€ข 3 min read โ€ข Read on X
There is a mathematical formula so beautiful that it is almost unbelievable.

Euler's identity combines the famous numbers ๐‘’, ๐‘–, ฯ€, 0, and 1 in a single constellation. At first sight, most people doubt that it is true. Surprisingly, it is.

This is why.

๐Ÿงต ๐Ÿ‘‡๐Ÿฝ
Let's talk about the famous exponential function ๐‘’หฃ first.

Have you ever thought about how is this calculated in practice? After all, raising an irrational number to any power is not trivial.

It turns out that the function can be written as an infinite sum!
In fact, this can be done with many other functions.

For those that are differentiable infinitely many times, there is a recipe to find the infinite sum form. This form is called the Taylor expansion.

It does not always yield the original function, but it works for ๐‘’หฃ.
Taylor expansions are advantageous for two reasons.

First, we can approximate functions by cutting of the sum at some N.

Second, we can simply extend functions to the complex plane with this formula!
The exponential function is not the only one that can be written as a Taylor series.

We can also do this with the trigonometric functions sine and cosine.

(Feel free to check this by hand using the general Taylor expansion formula.)
By plugging in ๐‘–๐‘ง into the exponential function, we discover that the complex exponential function can be written in terms of trigonometric functions!

(We use that ๐‘–ยฒ = -1.)
In the special case ๐‘ง = ฯ€, we obtain the famous formula called Euler's identity.

This is how the magic happens.
When asked, Euler's identity often comes up among mathematicians as the most beautiful formula ever.

It is not only amazing because it connects together a bunch of famous constants, but because it establishes a connection between the exponential and trigonometric functions.
If you enjoyed this explanation, consider following me and hitting a like/retweet on the first tweet of the thread!

I regularly post simple explanations of mathematical concepts in machine learning, make sure you don't miss out on the next one!

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More from @TivadarDanka

Jan 20
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 ๐‘–-th row and ๐‘—-th column corresponds to an edge going from ๐‘– to ๐‘—.
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
Jan 14
Matrix multiplication is not easy to understand.

Even looking at the definition used to make me sweat, let alone trying to comprehend the pattern. Yet, there is a stunningly simple explanation behind it.

Let's pull back the curtain! Image
First, the raw definition.

This is how the product of A and B is given. Not the easiest (or most pleasant) to look at.

We are going to unwrap this. Image
Here is a quick visualization before the technical details.

The element in the i-th row and j-th column of AB is the dot product of A's i-th row and B's j-th column. Image
Read 17 tweets
Jan 8
Behold one of the mightiest tools in mathematics: the camel principle.

I am dead serious. Deep down, this tiny rule is the cog in many methods. Ones that you use every day.

Here is what it is, how it works, and why it is essential: Image
First, the story:

The old Arab passes away, leaving half of his fortune to his eldest son, third to his middle son, and ninth to his smallest.

Upon opening the stable, they realize that the old man had 17 camels. Image
This is a problem, as they cannot split 17 camels into 1/2, 1/3, and 1/9 without cutting some in half.

So, they turn to the wise neighbor for advice. Image
Read 18 tweets
Jan 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 ๐‘–-th row and ๐‘—-th column corresponds to an edge going from ๐‘– to ๐‘—.
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
Dec 11, 2025
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 ๐‘–-th row and ๐‘—-th column corresponds to an edge going from ๐‘– to ๐‘—.
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
Dec 9, 2025
Matrix multiplication is not easy to understand.

Even looking at the definition used to make me sweat, let alone trying to comprehend the pattern. Yet, there is a stunningly simple explanation behind it.

Let's pull back the curtain! Image
First, the raw definition.

This is how the product of A and B is given. Not the easiest (or most pleasant) to look at.

We are going to unwrap this. Image
Here is a quick visualization before the technical details.

The element in the i-th row and j-th column of AB is the dot product of A's i-th row and B's j-th column. Image
Read 17 tweets

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