[Tex/LaTex] Vertical bar with appropriate length

math-mode

I have a scenario in which I need to create a vertical bar that its size is in the length of 3 rows.

My code is: 

\begin{align*}
\begin{cases}
x = 2t + 1\\
y = t + 2\\
z = 3
\end{cases}
 & \Bigg | \quad t\in \mathbb R
\end{align*}

I'm familiar with the possibility to set its size in centimetres.
Though I prefer to use something similar to \middle.
Problem is that in this case, I don't have \right and \left, so that \middle is meaningless (and yield an error).

Note: I'm using the TexMaths plugin of LibreOffice, which uses the standard latex program.

Best Answer

You can use a \vphantom of the cases environment to adjust the size of \left (or \right) to suit your needs:

enter image description here

\documentclass{article}
\usepackage{amsmath,amssymb}
\begin{document}

\begin{align*}
  \begin{cases}
    x = 2t + 1 \\
    y = t + 2 \\
    z = 3
  \end{cases}
  & \left.\kern-\nulldelimiterspace
  \vphantom{\begin{cases}
    x = 2t + 1 \\
    y = t + 2 \\
    z = 3
  \end{cases}}\right| \quad t \in \mathbb{R}
\end{align*}

\end{document}

I've just duplicated the cases inside a \vphantom (zero-width \phantom) and corrected for the \left. "null" delimiter. Of course, it's not really all than necessary to use align* as there's no multiline equation alignment required:

\documentclass{article}
\usepackage{amsmath,amssymb}
\begin{document}

\[
  \left.\begin{cases}
    x = 2t + 1 \\
    y = t + 2 \\
    z = 3
  \end{cases}
  \right| \quad t \in \mathbb{R}
\]

\end{document}
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