You have come to the right place. In this content, the calligraphic font style is represented by the `\mathcal{}`

command. For your convenience, various problems have been solved, which you face.

However, this command is only valid for math mode.

## Use mathcal command for Calligraphic font

The usage of this symbol is much more in terms of usage. For example, the use of this symbol is noticed in different cases, from mathematically normal distribution to Big o notation and topology.

```
\documentclass{article}
\begin{document}
$$ ABCDEF \quad \mathcal{ABCDEF} $$
$$ \mathcal{O},\mathcal{T},\mathcal{P},\mathcal{N} $$
$$ \mathcal{N}\quad\mathcal{A}f(x)\quad\mathcal{F} $$
$$ X^2/\sigma^2 \sim \mathcal{X}^2(\mu^2/\sigma^2) $$
$$ \ln \mathcal{L}(\mu ,\sigma^2) $$
\end{document}
```

**Output : **

## Lowercase Calligraphic fonts

`\mathcal{}`

commands have some limitations. Because even if the capital alphabet is converted to this font. Cannot convert digits and small alphabets to calligraphy fonts.

```
\documentclass{article}
\usepackage{amssymb}
\begin{document}
$$ \verb|\mathcal{abcd}|\dashrightarrow \mathcal{abcd} $$
$$ \verb|\mathcal{1234}|\dashrightarrow\mathcal{1234} $$
$$ \verb|\mathcal{ABCDefgh}|\dashrightarrow\mathcal{ABCDefgh} $$
\end{document}
```

**Output : **

## Calligraphic bold font style

You will see many commands that convert text or math expressions to bold font style like `\textbf{}`

, `\mathbm`

, `bf`

etc. However, in the case of calligraphy font style, `\boldsymbol`

should be used which will convert the font style of the symbol to bold.

Because if you use another command instead of `\boldsymbol`

, the output will show an arrow.

```
\documentclass{article}
\usepackage{amsmath}
\begin{document}
$$ S\in \boldsymbol{\mathcal{P}}_d $$
$$ \theta,x\in\boldsymbol{\mathcal{X}} $$
$$ \boldsymbol{\mathcal{P}}(X)\in\boldsymbol{\mathcal{X}} $$
\end{document}
```

**Output : **

## Big O notation and topology T denoted by mathcal command

Below are some examples of Big O notation and Topology T by this command.

```
\documentclass{article}
\begin{document}
$$ \mathcal{O},\;\mathcal{T} $$
$$ \mathcal{O}(|K|.g)=\mathcal{O}(g)\quad Q_i\in \mathcal{T} $$
$$ \mathcal{O}(\log n)\quad (\mathcal{T}_1 ,\mathcal{T}_2) $$
$$ \mathcal{O}(n^c)\quad (X,\mathcal{T}_2)\rightarrow (X,\mathcal{T}_1) $$
$$ f(n) = \mathcal{O}(n!) $$
\end{document}
```

**Output : **