Sometimes we need to put two dots above a letter in our writing or mathematical notation. This is especially needed for umlauts (like ä, ö, ü) or to show the second derivative in math. Additionally, names like “Schrödinger” use an umlaut, which is common in German and other languages.

Many people get confused about how to do this in LaTeX. Here, we will discuss four different methods to solve this problem using LaTeX.

## Using the \”{arg} ommand

The `\"{}`

command is the simplest and most common way to add two dots above a letter in LaTeX. This is mainly used in text mode.

\documentclass{article} \begin{document} Schr\"{o}dinger \\ Die M\"{a}dchen spielen drau\ss{}en im gr\"{u}nen Park. \end{document}

It is a effective method used in text mode. For example, `\"{u}`

will produce ü, and `\"{a}`

will produce ä, which are common in the German language.

## Using the \ddot{arg} Command

The `\ddot{}`

command is mainly used in mathematics. It is usually used to show the second derivative. For example, `\ddot{x}`

represents the second derivative of x. This is a very useful and effective method for mathematical notation.

\documentclass{article} \usepackage{amsmath} \begin{document} The double derivative of the function \( f(x) \) with respect to \( x \) is represented as: \[ \ddot{y} = \frac{d^2y}{dx^2} \] For example, the equation of motion for a simple harmonic oscillator is: \[ \ddot{x} + \omega^2 x = 0 \] \end{document}

## Using the \stackrel{..}{letter} Command

The `\stackrel{..}{}`

command allows you to stack two dots above a letter. This is often used for more complex customizations.

\documentclass{article} \usepackage{amsmath} \begin{document} This can be used to denote the second derivative of \( x \): \[ \stackrel{..}{x} = \frac{d^2a}{dt^2} \] \end{document}

This command stacks the `{..}`

part above the letter `{x}`

. It is used in various cases where you need to stack special symbols or marks above a letter.

For example, you can use `\stackrel{*}{a}`

to stack a star above a letter.

## Using the \overset{..}{letter} Command

The `\overset{..}{}`

command is similar to \stackrel{letter}, but it is generally more convenient for various customizations.

\documentclass{article} \usepackage{amsmath} \begin{document} The motion of a damped harmonic oscillator can be described by the following differential equation: \[ m\overset{..}{x} + c\overset{.}{x} + kx = 0 \] \end{document}

In this example, the `\overset{..}{x}`

is used to represent the second derivative of x with respect to time (acceleration), and `\overset{.}{x}`

is used to represent the first derivative of x with respect to time (velocity).

## Conclusion

There are different methods to add dots above a letter in LaTeX. Each method has its own use case, and you can use any method according to your needs.

The `\"{}`

command is generally used in text, the `\ddot{}`

command is used in math, and the `\stackrel{..}{}`

and `\overset{..}{}`

commands are used for customized marks or symbols.