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I wanted to write my equations with a left brace and text on the side left to my equations so I first used this code :

\[
\text{Sous contraintes}\left\{
    \begin{array}{ll}
    eq1 & conditions1\\
    eq2 & conditions2\\
    eq3 & conditions3\\
    \end{array}
    \right.
\]

Use of align but not numebered

However, I also need my equations to be numbered, so I tried empheq environment :

\begin{empheq}[left = \empheqlbrace]{align}
    eq1 && conditions1\\
    eq2 && conditions2\\
    eq3 && conditions3
\end{empheq}

Use of empeq but can't add text before brace

Which works for the numbered equations.

But I couldn't manage to add « Sous contraintes » (under constraints) on the left of my equations. How can I do this ? Morever, if « contraintes » could be just under « sous » (on a new line, but still on the left of the brace), it'll be perfect !

Thank you for your help !

1

Just add it to the left= key:

\documentclass[french]{article}

\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage[T1]{fontenc}
\usepackage{empheq}

\begin{document}

\begin{empheq}[left =\text{Sous contraintes} \empheqlbrace]{align}
eq1 && conditions1\\
eq2 && conditions2\\
eq3 && conditions3
\end{empheq}

\end{document} 

enter image description here

As suggested by @BambOo, you might want to number the conditions as 1a, 1b, 1c, nest the environment in subequations.

Another possibility is the numcases or subnumcases environment:

\usepackage{cases}
..................
\begin{subnumcases}{\text{Sous contraintes}}
eq1 & conditions1\\
eq2 & conditions2\\
eq3 & conditions3
\end{subnumcases}

enter image description here

  • Thank you Bernard ! That works perfectly. I added \parbox{8em}{Sous \\ contraintes} so the two words can be superposed – JKHA Jul 18 '18 at 9:29
  • You might want to have a 1.a, 1.b, 1.c numbering of your equations, in this case, wrap your empheq environment inside a subequations environment. – BambOo Jul 18 '18 at 9:47
  • It's indeed a better way of numbering, thank you @BambOo – JKHA Jul 18 '18 at 11:24

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