Matrix factorizations are the pinnacle results of linear algebra.
From theory to applications, they are behind many theorems, algorithms, and methods. However, it is easy to get lost in the vast jungle of decompositions.
This is how to make sense of them.
We are going to study three matrix factorizations:
1. the LU decomposition, 2. the QR decomposition, 3. and the Singular Value Decomposition (SVD).
First, we'll take a look at LU.
1. The LU decomposition.
Let's start at the very beginning: linear equation systems.
Linear equations are surprisingly effective in modeling real-life phenomena: economic processes, biochemical systems, etc.
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!
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.
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.