[Tex/LaTex] Package amsmath Error: \begin{aligned} allowed only in math mode

errors

The display pdf is ok but i receive the following error message :

! Package amsmath Error: \begin{aligned} allowed only in math mode.

\documentclass[10pt,a4paper]{book}

\usepackage[utf8x]{inputenc}
\usepackage[greek]{babel}
\usepackage{amssymb,amsmath,latexsym,amsfonts,amsthm,cleveref}
\newcommand{\abs}[1]{ \left\lvert#1\right\rvert} 
\newcommand{\norm}[1]{\left\lVert#1\right\rVert} 

\begin{document}

\begin{aligned}
\norm{xy}_{\mathbb{H}}^4 ={} &  \abs{z+w}^4 + 16(x_3 + y_3 - \frac{1}{2}Im(z\bar{w}))^2  \\
     & = \abs{ \abs{z+w}^2 + 4i(x_3 + y_3 - \frac{1}{2}Im(z\bar{w}))}^2}) \\
      & = \abs{ \abs{z}^2 + 4ix_3 + 2z\bar{w} + \abs{w}^2+ 4iy_3 }^2 \\
      & \leq (\abs{ \abs{z}^2 + 4ix_3} + 2\abs{\bar{z}}\abs{w} + \abs{ \abs{w}^2 +4iy_3})^2 \\ & = (\norm{x}_\mathbb{H}^2 + 2 \abs{\bar{z}}\abs{w} + \norm{y}_\mathbb{H}^2)^2 \\
      & \leq ( \norm{x}_\mathbb{H} + \norm{y}_\mathbb{H})^4. 
\end{aligned}

\end{document}

Best Answer

Use \begin{align*} ... \end{align*} instead of aligned so you won't need to put everything inside math mode.

Related Solutions

[Tex/LaTex] error with math mode

You need to be careful to use mathmode correctly; in particular, \mathbb needs to be in mathmode.

You didn't specify what the macro \D does, but it looks as if would you like to use the align environment, as follows

\documentclass{article}

\usepackage{amssymb}
\usepackage{amsmath}
\newcommand{\D}{D}

\begin{document}
 Given a curve $\mathcal{L}$, define two functions of distance transform $\kappa_{+}$ 
 and $\kappa_{-}$ on $\mathbb{R}^{2}$ as 
 \begin{align}
 \kappa_{+}(x) & = d(x,\mathbb{R}^{2}\D), x \in \mathbb{R}^{2} \\
 \kappa_{-}(x) & = d(x,\mathbb{R}^{2}\D), x \in \mathbb{R}^{2}
 \end{align}
\end{document}

[Tex/LaTex] ! Package amsmath Error: \tag not allowed here

You're still using inline math. (La)TeX distinguishes between math that is supposed be written on a line of text, delimited by $ ... $ or $ ... $, and displayed math, which is placed on its own paragraph.

For a single unnumbered, displayed equation you can use \[ ... \], for a numberered equation there is \begin{equation} ... \end{equation}. For sets of equations, or multiline equations, amsmath provides several environment, including align and gather, as well as the starred forms align* and gather* that are unnumbered.

Displayed equations are by default centered, to make them left-aligned add fleqn as an option to amsmath or the document class, e.g. \usepackage[fleqn]{amsmath}.

For more information about amsmath, read the manual. For math typesetting in general, you could take a look at Herbert Voss' Mathmode.

A demonstration with your example:

\documentclass{article}
\usepackage{amsmath}

\begin{document}
Now solve for $E[X]$:
\begin{gather}
E[X] = 1 + E[X] - p \cdot E[X] \\
0 = 1 - p \cdot E[X]\tag{"xyz"} \\
p \cdot E[X] = 1\tag{"xyy"} \\
E[X] = \frac{1}{p}\tag{"xzy"}
\end{gather}

Now solve for $E[X]$:
\begin{align}
E[X] &= 1 + E[X] - p \cdot E[X] \\
0 &= 1 - p \cdot E[X]\tag{"xyz"} \\
p \cdot E[X] &= 1\tag{"xyy"} \\
E[X] &= \frac{1}{p}\tag{"xzy"}
\end{align}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] error with math mode

[Tex/LaTex] ! Package amsmath Error: \tag not allowed here

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