Tivadar Danka Profile picture
Apr 27, 2021 6 tweets 2 min read Read on X
Have you ever wondered why include the logarithm in the definition of log-likelihood?

The answer is simple: logarithm makes differentiation of products easier.

Let's see why!

🧵 👇🏽
Although the derivative of a sum is the sum of derivatives, a similar property cannot be stated about the product of functions.

The derivative of a product is slightly more complicated: it is a sum of products.
The formula gets even more complicated when we have more functions in the product.

When potentially hundreds of terms are present, like in the likelihood function, computing this is not feasible.
This is where taking the logarithm can help us: it turns multiplication into addition!
So, instead of differentiating a product of 𝑛 functions, we have to deal with the sum!

Since the logarithm strictly increasing, it won't interfere with optimization either: the optimums are attained at the same place.
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 seemingly complicated concepts in machine learning, make sure you don't miss out on the next one!

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More from @TivadarDanka

Oct 14
In machine learning, we use the dot product every day.

However, its definition is far from revealing. For instance, what does it have to do with similarity?

There is a beautiful geometric explanation behind: Image
By definition, the dot product (or inner product) of two vectors is defined by the sum of coordinate products. Image
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First, the dot product is linear in both variables. This property is called bilinearity. Image
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Oct 13
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This is how to make sense of them. Image
We are going to study three matrix factorizations:

1. the LU decomposition,
2. the QR decomposition,
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First, we'll take a look at LU.
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Oct 11
Behold one of the mightiest tools in mathematics: the camel principle.

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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.

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So, they turn to the wise neighbor for advice. Image
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Oct 9
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
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Oct 8
Graph theory will seriously enhance your engineering skills.

Here's why you must be familiar with graphs: Image
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They are all networks that establish relationships between objects. Image
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Oct 7
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Here is what's behind the magic:
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You can imagine this as a rectangular dartboard. Image
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Again, you can imagine this as closing your eyes, doing a 360° spin, then launching a dart.

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