Math & Science ⇒ Vector and temporal Derivative with Dot

[perku]

Hi everybody,

We have a problem when we want to write the temporal derivative of a vector with a dot and when in the vector there is a dotted component, for example:

Code: Select all

\dot{\begin{bmatrix}z \\ \dot{z} \end{bmatrix}}

The result is that the second component of the vector is moved up and right. It can be shown in the attached image.

Is there any way to do it correctly?


Thank you very much
Aitor

[Stefan Kottwitz]

Hi Aitor,

welcome to the board!

The problem here is caused by nesting the \dot command. It can be fixed by using a box. Here's away which defines an outer dot command, which you can use with the normal \dot:

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\newsavebox{\dotbox}
\newcommand{\outerdot}[1]{%
  \sbox\dotbox{$#1$}\dot{\usebox\dotbox}}
\begin{document}
\[
  \outerdot{\begin{bmatrix} z \\ \dot{z} \end{bmatrix}}
\]
\end{document}

Stefan

[perku]

Hi Stefan

Thank you very much, now my equations will be correct.

Aitor