doc/mymath.sty

\ProvidesPackage{mymath}

\usepackage{euler}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{bbm}

\newcommand{\matTT}[9]{
\[
\left|\begin{array}{ccc}
 #1 & #2 & #3\\
 #4 & #5 & #6\\
 #7 & #8 & #9
\end{array}\right|
\]
}

\newcommand{\fork}[4]{
  \left\{
  \begin{array}{l l}
  #1 & \mbox{#2}\\
  #3 & \mbox{#4}\\
  \end{array} \right.}
\newcommand{\forkthree}[6]{
  \left\{
  \begin{array}{l l}
  #1 & \mbox{#2}\\
  #3 & \mbox{#4}\\
  #5 & \mbox{#6}\\
  \end{array} \right.}

\newcommand{\vecthree}[3]{
\begin{bmatrix}
 #1\\
 #2\\
 #3
\end{bmatrix}
}

\newcommand{\vecthreethree}[9]{
\begin{bmatrix}
 #1 & #2 & #3\\
 #4 & #5 & #6\\
 #7 & #8 & #9
\end{bmatrix}
}