math-modematrices
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.
\begin{align*}
\pi(X)f(x) = \frac{d}{dt}\Pi(e^{tX})\vert_{t=0} f(x) &= \frac{d}{dt}(\Pi(e^{tX})f(x))\vert_{t=0})= \\
&=\frac{d}{dt}(f(e^{-tX}x))\vert_{t=0}\\
&= \nabla_{\xi} f \left(-
\left( \begin{array}{ccc}
X_{11} & \cdots & X_{1n} \\
\vdots & \cdots & \vdots \\
X_{n1} & \cdots & X_{nn}
\end{array} \right)
\left( \begin{array}{c}
\xi_1 \\
\vdots \\
\xi_n
\end{array} \right)
\right)\\
&= -\sum_{i,j}X_{ij}\xi_j \frac{\partial f}{\partial \xi_i}
\end{align*}
If using a Times Roman font instead of Computer Modern is an option for you, you may want to look into using the MathTime Professional II math font package to achieve your objective. Its square brackets are satisfyingly thick even at the smallest sizes.
Note that while the full MathTime Pro II package isn't free of charge, its "lite" subset, which is all that's needed in this case, is free of charge.
\documentclass{article}
\usepackage{amsmath}
\usepackage[lite]{mtpro2}
\begin{document}
\[
\begin{bmatrix} A & B & C & D \end{bmatrix}
\begin{bmatrix} u \\ v \\ w \\ y \end{bmatrix}
= 0.
\]
\end{document}
Best Answer
You can use an array to create a vector. See section 3 of the Not so Short Guide to LaTeX for more details.
The spacing around between the elements and the brackets can be reduced by replacing
{c}with{@{}c@{}}. You could also consider using thebmatrixenvironment 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.