I used the Daum Equation Editor to create the following formula:

enter image description here

This was the generated Tex:

{ f }_{ LR\_ FI }\left( x \right) =\left\{ 
L\left( \frac { { m }_{ l }-x }{ \alpha  }  \right) ,x\le { m }_{ l },\\ 
1,{ m }_{ l }\le x\le { m }_{ r },\\ 
R\left( \frac { x-{ m }_{ r } }{ \beta  }  \right) ,x\ge m \right 

In the Latex editor however, I get the following error:

Missing delimiter (. inserted).
<to be read again> 
l.1288 ...} }{ \beta  }  \right) ,x\ge m \right \]

provided that the Tex in in math mode.

Why am I getting this error, and how can I get it solved?


  • 1
    it would be a lot easier for people to help you if you provided an example that could be run to produce the error. presumably you have more \left than \right (but most of the \left and \right are incorrect and should be deleted \left( x \right) is wrong and should be (x) Apr 22, 2018 at 20:36
  • 7
    oh, your final \right is missing a . it should be \right . (but it would be better to use a cases environment) Apr 22, 2018 at 20:38
  • @Simplicity Why use you Daum Equation Editor? You could try latex4technics.com
    – Sebastiano
    Apr 22, 2018 at 21:29
  • @DavidCarlisle I had to have a "." after the last \right. The issue is that I have all the lines beside each other rather on new lines. Any ideas why is that? Thanks.
    – Simplicity
    Apr 22, 2018 at 22:16
  • 1
    Yes you should provide a complete test document that produces the error (see Bernard's answer) otherwise you make people guess what you did wrong, did you not put the fragment in a math enviornment?, did you not include some needed package? etc and make everyone have to invent and type out a required preamble. (Or more likely they do not do that and so you do not get an answer, although Bernard answered this time) In this case the issue about line breaking is precisely because of code you have not shown. If we guess that you put the fragment in an environment where \\ does not work. Apr 23, 2018 at 6:36

2 Answers 2


The final \right was missing a .. But anyway, one can obtain a nicer result.

Here are three ways to obtain such a nicer result, with a lighter code, based either on the dcasesenvironment from mathtools or on alignat and package empheq (which loads mathtools), combined with package eqparbox for a nicer alignment (due to the length difference of the middle row w..r.t. the upper and lower rows:

\usepackage{newtxtext, newtxmath}

\usepackage{mathtools, nccmath, empheq}
\newcommand{\eqmathbox}[2][M]{\eqmakebox[#1]{$\displaystyle #2$}}

\begin{document} %

\[ f_{ LR\_ FI }(x ) = \begin{dcases}
\eqmathbox{L\Bigl( \frac {m_{l}-x }{\alpha} \Bigr),} & x \le m_{ l }, \\
\eqmathbox{1,} & m_{l} \le x \le m_{r},\\
\eqmathbox{R\Bigl( \frac{x - m_{r}}{\beta}\Bigr),} & x \ge m_{r}. 
\end{dcases} \]%

\[ f_{ LR\_ FI }(x ) = \begin{dcases}
\eqmathbox{ L\Bigl( \frac {m_{l}-x }{\alpha} \Bigr),} & \eqmathbox[C]{x \le m_{ l },} \\
\eqmathbox{1,} & \eqmathbox[C]{ m_{l} \le x \le m_{r},}\\
\eqmathbox{R\Bigl( \frac{x - m_{r}}{\beta}\Bigr),} & \eqmathbox[C]{x \ge m_{r}.} 
\end{dcases} \]%

\begin{empheq}[left={f_{ LR\_ FI }(x ) = \empheqlbrace}]{alignat* = 2}
 & \eqmathbox{ L\Bigl( \frac {m_{l}-x }{\alpha} \Bigr),} &\quad x & \le m_{ l }, \\
 & \eqmathbox{1,} & m_{l} & \le x \le m_{r},\\
 & \eqmathbox{R\Bigl( \frac{x - m_{r}}{\beta}\Bigr),} & x & \ge m_{r}. 


enter image description here


Some suggestions:

  • Don't overuse \left and right to auto-size parentheses -- quite often, it's better to impose a fixed size

  • Don't needlessly use curly braces to encase various items -- overuse of {and } makes the code harder, not easier, to read

  • Encase the string LR\_FI in a \mathit (or \mathrm, if you prefer) statement, for a more compact "look"

  • For a more-compact appearance, consider using inline-fraction notation instead of \frac{...}{...}

  • Do familiarize yourself with the amsmath package and its cases environment as well as the mathtools package (a superset of the amsmath package) and its cases* environment

enter image description here

\usepackage{mathtools} % for 'cases*' environment
\usepackage{newtxtext,newtxmath} % optional -- Times Roman clone
f_{\mathit{LR\_FI}}^{}(x) =
L((m_l-x)/\alpha) & if $x\le m_l$\,, \\
1                 & if $m_l\le x\le m_r$\,, \\
R((x-m_r)/\beta)  & if $x\ge m$\,.

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