# Writing left side of the CASES brackets

I want to write something on the left side of the cases brackets like shown in the picture. The code I am using:

$$\begin{split} & E(T,\alpha) = \\ & \begin{cases} 1 & \text{\alpha < \alpha_{vi}} \\ \textrm{E_0(T)} & \textrm{\alpha = \alpha_{vi}}\\ \text{E_0(T) + (\alpha-\alpha_{vi})(E_\infty(T)-E_{0}(T))} & \text{\alpha_{vi} < \alpha < 1}\\ \text{E_\infty(T)} & \text{\alpha = 1} \end{cases} \end{split} \label{eq:chile}$$


I want to add the letters in red:

• Unrelated, why \textrm{$\alpha$ = $\alpha_{vi}$} and not \alpha = \alphs_{vi}? Why all these \textrm and \text commands here in the first place. They are not doing anything. Mar 22 at 11:19

## 3 Answers

One possibility is:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
$$\begin{split} & E(T,\alpha) = \\ & \begin{matrix} \textsf{I} \\[0.5ex] \textsf{II} \\[0.5ex] \textsf{III} \\[0.5ex] \textsf{IV} \end{matrix}\quad \begin{cases} 1 & \text{\alpha < \alpha_{vi}} \\ \textrm{E_0(T)} & \textrm{\alpha = \alpha_{vi}}\\ \text{E_0(T) + (\alpha-\alpha_{vi})(E_\infty(T)-E_{0}(T))} & \text{\alpha_{vi} < \alpha < 1}\\ \text{E_\infty(T)} & \text{\alpha = 1} \end{cases} \end{split}$$
\end{document}


• Wow that was fast. It seems pretty obvious now, thank you! I'm still a newbie...
– Fel
Mar 22 at 10:28
• @Fel, you are welcome! Mar 22 at 10:29

A possibility with {NiceArray} of nicematrix. The output will be correct even if you change the height or the depth or the rows of array.

 \documentclass{article}
\usepackage{nicematrix}

\begin{document}

$$\begin{split} & E(T,\alpha) = \\ & \begin{NiceArray}{>{\color{red}}llc} \text{I} & 1 & \alpha < \alpha_{vi} \\ \text{II} & E_0(T) & \alpha = \alpha_{vi}\\ \text{III} & E_0(T) + (\alpha-\alpha_{vi})(E_\infty(T)-E_{0}(T)) & \alpha_{vi} < \alpha < 1 \\ \text{IV} & E_\infty(T) & \alpha = 1 \CodeAfter \SubMatrix{\{}{1-2}{4-2}{.} \end{NiceArray} \end{split} \label{eq:chile}$$

\end{document}


You need several compilations (because nicematrix uses PGF/Tikz under the hood).

Still another solution, without cases, replaced with blkarray and the bigdelim package:

\documentclass{article}
\usepackage{amsmath}
\usepackage{blkarray}
\usepackage{bigdelim}
\usepackage[svgnames]{xcolor}

\begin{document}

$$\begin{split} & E(T,\alpha) = \\ & \begin{blockarray}{>{\color{IndianRed}\mathsf{\Roman{BAenumi}}}l@{\;}c@{}ll} & \ldelim\{{4}{*}& 1 & \alpha < \alpha_{vi} \\ & & E_0(T) & \alpha = \alpha_{vi} \\ & & E_0(T) + (\alpha-\alpha_{vi})(E_\infty(T)-E_{0}(T)) & \alpha_{vi} < \alpha < 1 \\ & & E_\infty(T) & \alpha = 1 \end{blockarray} \end{split}$$

\end{document}


• @daleif: It seems I had (again) a copy-paste accident. I'll fix it within seconds. Thanks for warning me! Mar 22 at 11:19