[Tex/LaTex] Defining absolute value in scrbook

math-mode

Why does this not work in scrbook:

\[
\left | x \right |=\left\{\begin{matrix} x, if x\geq 0
\\ -x, if x<0 \end{matrix}\right.
\]

(I wrote it in writeLaTeX.)

if I use the amsmath then bring up a message:

"(no line number in this file):

LaTeX Error: Command \ iiint already defined.

Or name \ end … illegal, see p.192 of the manual.

See the LaTeX manual or LaTeX Companion for explanation. Type H for immediate help. …

l.507 … {\ iiint} {\ DOTSI \ protect \ MultiIntegral {3}}

Your command was ignored. Type I to replace it with another command, or to continue without it."

The codes I've used:

\documentclass[oneside]{scrbook} 
\usepackage{etoolbox} 
\usepackage{helvet} 
\usepackage[bahasa]{babel} 
\usepackage{calc} 
\usepackage[usenames,dvipsnames]{xcolor} 
\usepackage[utf8]{inputenc} 
\usepackage{chngcntr} 
\usepackage{graphicx} 
\usepackage{enumerate} 
\usepackage[inline,shortlabels]{enumitem} 
\usepackage{pifont} 
\usepackage{wasysym} 
\usepackage{sectsty} 
\usepackage{amssymb} 
\usepackage{array} 
\usepackage{venndiagram} 
\usepackage{tcolorbox} 
\usepackage{comment} 
\specialcomment{solusi}{\begin{tcolorbox}}{\end{tcolorbox}}

Best Answer

You're missing a backslash character, \, between \left and {.

However, rather than just adding the missing backslash character, you may want to rewrite the entire expression to make use of the cases environment to obtain an overall better format.

enter image description here

\documentclass{scrbook}
\usepackage{amsmath}
\begin{document}
Original form, with backslash inserted after second \texttt{\textbackslash left}:
\[
\left| x \right|=
\left\{
  \begin{matrix} x, if x\geq 0\\ -x, if x<0 \end{matrix}
\right.
\]

\bigskip
Modified form, using \texttt{cases} environment:
\[
\left | x \right | = 
\begin{cases}
\hfill x & \text{if $x\geq 0$}\\
      -x & \text{if $x<0$}
\end{cases}
\] 
\end{document}

Related Solutions

[Tex/LaTex] how to write a limit and how to use large absolute value

For the first question, you can typeset limits using the \lim command:

$\lim_{x\to\infty}\frac{1}{x}$

\[ \lim_{x\to\infty}\frac{1}{x} \]

For the second question, the \left, \middle and \right commands can be used to achieve vertical extension of some delimiters:

\[ \left\lvert\frac{1}{2} \right\rvert \]

To obtain fine control on the size of extensible delimiters there are also the following command groups (which in some circumstances, must replace the \left \middle \right construct):

\bigl - \bigm - \bigr
\Bigl - \Bigm - \Bigr
\biggl - \biggm - \biggr
\Biggl - \Biggm - \Biggr

These groups provide delimiters of increasing sizes; the first column gives four sizes of opening symbols; the second column gives four sizes of relation symbols, and the third column gives four sizes of closing symbols..

There are some cases in which the above commands should replace the \left, \right ones: when the latter produce delimiters which are too big, and when there are several delimiters together. Compare the result of

\[ \left\lvert\lvert x\rvert -\lvert y\rvert \right\rvert \]

and

\[ \bigl\lvert\lvert x\rvert -\lvert y\rvert \bigr\rvert \]

In the first case, the inner and outer delimiters have the same size and the result can be ambiguous; in the second case, the outer delimiters are bigger, improving readability.

[Tex/LaTex] Absolute Value Symbols

I have been using the code below using \DeclarePairedDelimiter from the mathtools package.

Since I don't think I have a case where I don't want this to scale based on the parameter, I make use of Swap definition of starred and non-starred command so that the normal use will automatically scale, and the starred version won't:

enter image description here

If you want it the other way around comment out the code between \makeatother...\makeatletter.

\documentclass{article}
\usepackage{mathtools}

\DeclarePairedDelimiter\abs{\lvert}{\rvert}%
\DeclarePairedDelimiter\norm{\lVert}{\rVert}%

% Swap the definition of \abs* and \norm*, so that \abs
% and \norm resizes the size of the brackets, and the 
% starred version does not.
\makeatletter
\let\oldabs\abs
\def\abs{\@ifstar{\oldabs}{\oldabs*}}
%
\let\oldnorm\norm
\def\norm{\@ifstar{\oldnorm}{\oldnorm*}}
\makeatother

\newcommand*{\Value}{\frac{1}{2}x^2}%
\begin{document}
    \[\abs{\Value}  \quad \norm{\Value}  \qquad\text{non-starred}  \]
    \[\abs*{\Value} \quad \norm*{\Value} \qquad\text{starred}\qquad\]
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] how to write a limit and how to use large absolute value

[Tex/LaTex] Absolute Value Symbols

Related Question