How to define horizontal and vertical curly braces ? Answer is here !!!

Vertical curly braces

To define a left vertical curly brace we use the attribute

\left\{

to close it we use

\right\}

To do not close ou do not open one of it, we use the dot attribute . For example:

$$
\sigma(s,i) = \left\{
    \begin{array}{ll}
        \tau_{si} & \mbox{si } \{s,i\} \in E \\
        \infty & \mbox{sinon.}
    \end{array}
\right.
$$
\[\sigma(s,i) = \left\{ \begin{array}{ll} \tau_{si} & \mbox{si } \{s,i\} \in E \\ \infty & \mbox{sinon.} \end{array} \right.\] 
$$
 \left.
    \begin{array}{ll}
        \tau_{si} & \mbox{si } \{s,i\} \in E \\
        \infty & \mbox{sinon.}
    \end{array}
\right \}=\sigma(s,i) 
$$
\[\left. \begin{array}{ll} \tau_{si} & \mbox{si } \{s,i\} \in E \\ \infty & \mbox{sinon.} \end{array} \right \}=\sigma(s,i)\]

Horizontal curly braces

For horizontal curly braces, we use the fonctions

\underbrace{...}
\overbrace{...}
$$
\underbrace{\ln \left( \frac{5}{6} \right)}_{\simeq -0.1823} \lt \overbrace{\exp \left(\frac{1}{2} \right)}^{\simeq 1.6487}
$$
\[\underbrace{\ln \left( \frac{5}{6} \right)}_{\simeq -0.1823} \lt \overbrace{\exp \left(\frac{1}{2} \right)}^{\simeq 1.6487}\]