Why does \\ not return a new line in an equation?

Question

\begin{equation*}\label{eq:pareto mle2}
A_0 = \frac{1}{(\alpha+t_x)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x} \right ) "\\\" <br>
 - \frac{1}{(\alpha+T)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T} \right ),
\end{equation*}

This is my code why \\ does not go to new line? How should I make it?

Answer 1

Both equation and equation* do not allow multi lined expressions. Use aligned from amsmath, inside equation* to break in to many lines. If alignment is not needed, you can use gathered (instead of aligned) as suggested by Mico.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
  \begin{equation*}\label{eq:pareto mle2}
  \begin{aligned}
A_0 = \frac{1}{(\alpha+t_x)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x} \right ) \\
 - \frac{1}{(\alpha+T)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T} \right ),
 \end{aligned}
\end{equation*}
\end{document}

Or use multlined from mathtools:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
  \begin{equation*}\label{eq:pareto mle2}
  \begin{multlined}
A_0 = \frac{1}{(\alpha+t_x)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x} \right ) \\
 - \frac{1}{(\alpha+T)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T} \right ),
 \end{multlined}
\end{equation*}
\end{document}

Answer 2

The amsmath package provides quite a few environments that help typeset equations that need to be split across two or more lines. The align* environment may be particularly suitable for the case at hand. In the code posted below, note the use of the & symbol to state the alignment points.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}\label{eq:pareto mle2}
A_0 &=   \frac{1}{(\alpha+t_x)^{r+s+x}} ,{}_2 F_1\biggl( r+s+x,x+1;r+s+x+1;
         \frac{\alpha-\beta}{\alpha + t_x} \biggr)\
&\quad - \frac{1}{(\alpha+T)^{r+s+x}}   ,{}_2 F_1\biggl( r+s+x,x+1;r+s+x+1;
         \frac{\alpha-\beta}{\alpha + T}   \biggr),
\end{align}
\end{document}

Addendum: Note the close similarity of the outputs produced by the single align* environment in this answer and the nested pair of equation*/multlined environments in @HarishKumar's answer.

Answer 3

There is an easy way to make \\ works in equation (change line):

\begin{equation}
  a = b
\end{equation}

Change it to

\begin{equation}
  \begin{array}{l}
    a = \\ 
    b
  \end{array}
\end{equation}

Answer 4

To obtain multi-lined expressions with equation number written beside, use the following code;

\documentclass{article}
\usepackage{mathtools}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\label{eq:1}
\begin{aligned}
A_0 = \frac{1}{(\alpha+t_x)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x} \right ) \\
 - \frac{1}{(\alpha+T)^{r+s+x}}{}_2F_1\left(r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T} \right ),
\end{aligned}
\end{equation}
\end{document}

Answer 5

Old topic, but without really satisfactory answers, in my opinion.

I'd go with multline, which has been introduced exactly for cases such as the present one. On the other hand, also split may be considered worth of use in this case, particularly in the third example, where the alignment is on the right, underlining the similarity between the two parts.

\documentclass{article}
\usepackage{amsmath}
\usepackage{leftidx}
\newcommand{\hg}[3][F]{\mathop{\leftidx{{#2}}{#1}{{#3}}\kern-\scriptspace}}
\begin{document}
\subsection*{\texttt{multline}}
\begin{multline}
A_0 =
  \frac{1}{(\alpha+t_x)^{r+s+x}} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x}
  \biggr) \
-\frac{1}{(\alpha+T)^{r+s+x}}{} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T}
  \biggr),
\end{multline}
\subsection*{\texttt{split} 1}
\begin{equation}
\begin{split}
A_0 &=
  \frac{1}{(\alpha+t_x)^{r+s+x}} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x}
  \biggr) \
&\qquad
-\frac{1}{(\alpha+T)^{r+s+x}}{} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T}
  \biggr),
\end{split}
\end{equation}
\subsection*{\texttt{split} 2}
\begin{equation}
\begin{split}
A_0 &=
  \frac{1}{(\alpha+t_x)^{r+s+x}} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x}
  \biggr) \
&
-\frac{1}{(\alpha+T)^{r+s+x}}{} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T}
  \biggr),
\end{split}
\end{equation}
\subsection*{\texttt{split} 3}
\begin{equation}
\begin{split}
A_0 =
  \frac{1}{(\alpha+t_x)^{r+s+x}} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + t_x}
  \biggr) \
-\frac{1}{(\alpha+T)^{r+s+x}}{} \hg{2}{1} \biggl(
    r+s+x,x+1;r+s+x+1;\frac{\alpha-\beta}{\alpha + T}
  \biggr)\makebox[0pt][l]{,}
\end{split}
\end{equation}
\end{document}

Points to note:

1. instead of {}_2F_1 that produces misaligned subscripts, I defined a command \hg (for hypergeometric);

2. \left and \right have been replaced by \biggl and \biggr;

3. if no numbering is wanted just add * to the name of the outer environment (multline* or equation*).