A Linear Map is invertable if it can be undone. It is called a nonsingular matrix

constituents

A linear map \(T \in \mathcal{L}(V,W)\)

requirements

A Linear Map \(T \in \mathcal{L}(V,W)\) is called invertable if \(\exists T^{-1} \in \mathcal{L}(W,V): T^{-1}T=I \in \mathcal{L}(V), TT^{-1} = I \in \mathcal{L}(W)\).

“a map is invertable if there is an inverse”: that combining the commutable inverse and itself will result in the identity map.

additional information

matrix invertability

Matrices whose determinants are not \(0\) (i.e. it is invertable) is called “nonsingular matrix”. If it doesn’t have an inverse, it is called a singular matrix.

For each term \(t\), let’s store all the documents containing \(t\). We identify each doc by DocID.

postings list

a “postings list” datastructure is a variable-length list which is appended to with “postings”. In this way, we can store a “posting” for every DocID with the index we encounter.

For instance, this could be a linked list.

Although: we generally want to sort our postings list by documentID for ease of indexing.

irrational numbers are real numbers that are not rational numbers.

Formally:

\begin{equation} \mathbb{C} = \mathbb{R} \backslash \mathbb{Q} \end{equation}

where, \(\backslash\) is subtracting two sets.