8

I'm trying to get the equation shown in the picture. But i only manage to get the following coding. Can anyone help me to label it with numbering like the picture? I tried with \begin{eqnarray} or \begin{equation} but end up with many errors.

\[ \left\{
  \begin{array}{lr}
    \dot {x}_1 = f_1(x_1,\dots,x_n) \\
     \hspace{13pt}   \dots \\
    \dot {x}_n = f_n(x_1,\dots,x_n)  \\
  \end{array}
\right.
\]

HELP

  • Welcome to TeX.SX! You can format TeX code by selecting it and clicking on the {} button (or adding four spaces in front of each line). Change \[ and \] into \begin{equation} and \end{equation} respectively. – egreg Dec 12 '13 at 10:22
  • @Andrew Ooi - Please see the startup guide ;) – Kiyoshi Dec 12 '13 at 18:52
10

Instead of inserting a row that starts with three horizontal dots, you could also create a row with a set of vertical dots centered on the = signs. The code below implements this idea via the \vdotswithin macro of the mathtools package.

enter image description here

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{equation}
    \begin{cases}
       \begin{aligned}
          \dot {x}_1 &= f_1(x_1,\dots,x_n) \\
          &\vdotswithin{=} \\  % vertical dots, centered on the "=" signs
          \dot {x}_n &= f_n(x_1,\dots,x_n)
       \end{aligned} 
    \end{cases}
\end{equation}
\end{document}
  • Don't forget \! before \begin{aligned}. – kiss my armpit Dec 12 '13 at 11:47
  • @DonutE.Knot In this case, it's not as necessary as in other cases, since aligned is not used inside one logical equation (where you need \!), rather it's used as it should be: to align multiple equations inside other math and the \{ is not part of the equations. Therefore I would advocate here for keeping the extra space. – yo' Dec 12 '13 at 12:15
9

Try with this code:

\documentclass{minimal}
\usepackage{amsmath}
\begin{document}

\begin{equation}
    \begin{cases}
        \dot {x}_1 = f_1(x_1,\dots,x_n) \\
        \ldots \\
        \dot {x}_n = f_n(x_1,\dots,x_n)
    \end{cases}
\end{equation}

\end{document}

You can also use your code, but with some changes (which egreg said):

\begin{equation}
    \begin{cases}
        \begin{array}{lr}
            \dot {x}_1 = f_1(x_1,\dots,x_n) \\
            \hspace{13pt}   \dots \\
            \dot {x}_n = f_n(x_1,\dots,x_n)  \\
        \end{array}
    \end{cases}
\end{equation}
  • 3
    equation should be used instead of align. – egreg Dec 12 '13 at 10:22
  • @egreg - Ok, I will change. – Kiyoshi Dec 12 '13 at 10:24

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