How can I type an expression of a column vector

Question

I want to type a column vector like below:

     [  dx     ]
UI = [  dy     ]
     [  dtheta ]

U is the name of this vector, and I is the subscript. Two brackets like the matrix style. dx, dy and dtheta are actually three items with a dot on their head, and theta is a Greek letter.

Answer 1

You can use an array to create a vector. See section 3 of the Not so Short Guide to LaTeX for more details.

\documentclass{article}
\begin{document}
\[
\mathbf{U}_I =
\left[
\begin{array}{c}
\mathrm{d}x \\
\mathrm{d}y \\
\mathrm{d}\theta
\end{array}
\right]
\]
\end{document}

The spacing around between the elements and the brackets can be reduced by replacing {c} with {@{}c@{}}. You could also consider using the bmatrix environment from the amsmath package. Note that \[ and \] create an equation that is not numbered. If you need a numbered equation you should use \begin{equation} and \end{equation} instead.

Answer 2

Is this what you're after?

\( U_i = \left[ \dot{dx}, \dot{dy}, \dot{d \theta} \right] \)

Well, you can replace the \[,\] with any other brace of your taste, e.g. \left(,\right) or \left\{,\right\}. In addition, instead of dx you can have something like \mathrm{d}x to have something similar to derivative.

In addition, if you wish you wish to have column vector, refer to this question and the answers following it.

Edit:

If you want to have a numbered version of the expression, put the expression between the \(, and \), that is what in the math-mode, inside an equation environment.