In LaTeX, you put a single dot on top of a character, most commonly within math mode, using the \dot command. This command is particularly useful for denoting time derivatives in physics and engineering.
Putting a Single Dot Over a Character in Math Mode
The primary command for placing a single dot over a character in LaTeX is \dot. This command is intended for use within LaTeX's math environment.
- Syntax:
$\dot{character}$ - Example: To place a single dot over the variable
x, you would write$\dot{x}$. - Usage: For instance,
\dot awill place a single dot over the letter 'a'. This is commonly used in physics for time derivatives, representing the first derivative with respect to time (e.g., velocity$\dot{x}$).
Placing Multiple Dots or Other Accents Over Characters
LaTeX provides various commands for placing dots and other accents above characters, extending beyond just a single dot. These are also primarily used in math mode.
Double Dots (\ddot)
When you need two dots over a character, perhaps to signify a second derivative with respect to time, you use the \ddot command.
- Syntax:
$\ddot{character}$ - Example: To place a double dot over the variable
y, you would write$\ddot{y}$. - Usage: Similarly,
\ddot aplaces a double dot over 'a', often representing a second derivative (e.g., acceleration$\ddot{x}$).
Other Common Over-Character Accents
Beyond single and double dots, LaTeX offers a rich set of commands for various accents and symbols to be placed above characters.
- Arrow (
\vec): To place an arrow over a character, use\vec a. This is frequently used for vector quantities (e.g.,$\vec{v}$for velocity vector). - Hat/Caret (
\hat): Used for unit vectors or estimated values (e.g.,$\hat{i}$,$\hat{p}$). - Tilde (
\tilde): Often used to denote a conjugate, a Fourier transform, or a statistical estimator (e.g.,$\tilde{x}$). - Bar/Overline (
\bar): Commonly used for complex conjugates, mean values, or negations (e.g.,$\bar{z}$,$\bar{X}$).
Here's a quick reference table for common over-character commands in math mode:
| Command | Output | Description |
|---|---|---|
\dot{x} |
$\dot{x}$ | Single dot (e.g., first time derivative) |
\ddot{x} |
$\ddot{x}$ | Double dot (e.g., second time derivative) |
\vec{a} |
$\vec{a}$ | Arrow (e.g., vector notation) |
\hat{x} |
$\hat{x}$ | Hat or caret (e.g., unit vector, estimator) |
\tilde{x} |
$\tilde{x}$ | Tilde (e.g., conjugate, transform) |
\bar{x} |
$\bar{x}$ | Bar or overline (e.g., mean, complex conjugate) |
\check{x} |
$\check{x}$ | Check |
\breve{x} |
$\breve{x}$ | Breve |
\acute{x} |
$\acute{x}$ | Acute accent (e.g., for phonetics) |
\grave{x} |
$\grave{x}$ | Grave accent (e.g., for phonetics) |
Dots Over Wider Expressions
The \dot and \ddot commands are designed for single characters. For placing dots (or other accents) over a wider expression that spans multiple characters, specialized commands are available, often requiring the amsmath or mathtools packages. For example, \widehat{XY} or \widetilde{XY} can place a hat or tilde over "XY", but direct "wide dot" commands are less common and typically require custom solutions or packages like accents for \overdot.
Practical Examples and LaTeX Code
To use these commands, simply ensure you are within a math environment, which can be inline (using $...$) or displayed (using \[...\] or \begin{equation}...\end{equation}).
\documentclass{article}
\usepackage{amsmath} % Recommended for advanced math typesetting
\begin{document}
In physics, velocity can be denoted as $\dot{x}$ and acceleration as $\ddot{x}$.
We can also represent a vector quantity, such as velocity, as $\vec{v}$.
Consider a unit vector $\hat{i}$ or an estimated parameter $\hat{\theta}$.
The complex conjugate of $z$ is often written as $\bar{z}$.
\begin{equation}
F = m\ddot{x} + k\dot{x} + cx
\end{equation}
Another example: a variable with a tilde $\tilde{y}$ and a check mark $\check{z}$.
\end{document}Key Considerations for Dot Placement
- Math Mode: Commands like
\dotand\ddotare specifically designed for and work only within LaTeX's math mode. - Text Mode Accents: For placing dots on top of letters in regular text (e.g., for specific languages like Polish 'ż' or Turkish 'i' with a dot), you would typically use language-specific commands or a dot accent like
\.{z}for the letter 'z'. However, the common interpretation of "put a dot on top in LaTeX" usually refers to the math mode context due to its frequent use in scientific notation.
For more detailed information on LaTeX commands and symbol usage, you can refer to the LaTeX Project website or comprehensive guides like Overleaf's LaTeX documentation on accents.
