Latex: how to break a line inside $$

I want to manually break a line inside $$:

$$something something <breakline> something else$$

I tried \\, \newline, and \linebreak bu开发者_运维技巧t none work. Ideas?

A couple of people have suggested eqnarray which will work, but a better approach is the align environment in the amsmath package.

\begin{align*}
something \\
something else
\end{align*}

If you want the two parts aligned in some way, use an & as described in the amsmath documentation.

Instead of using the TeX-style $$ commands, consider using the align* or gather* environments. Inside those, you can use the line break command \\.

(You will need to load the amsmath package to use those; but if you're doing any math at all, you should be loading that package regardless.)

11 years later...

An example of breaking text in multiple lines is having a cell with multiple lines in an array. Instead of using a new array row, you can break the text in lines within a cell. The advantage of doing this is interline space is not dependent on the whole row height (if some cell in the row has a large height, this won't influence the text interline space):

To do this, just enclose the cell content within curly braces and use \\ as a linebreak.

Content of the highlighted cell:

{ T_f (u) \text { is the transformed function and }
  \\
  K (t,u) \text { is the kernel used. }}

Whole code:

$\begin {array} {lll}
\text {Transform: } T_f (u) 
    & = \int \limits_{t_1}^{t^2} K (t,u) f(t) dt \;\; \textrm {where:}
        & {
            T_f (u) \text { is the transformed function and }
            \\
            K (t,u) \text { is the kernel used. }
          }
          \\
\text {Inverse transform: } f(u) 
    & = \int \limits_{u_1}^{u^2} K^{-1} (t,u) T_f(u) du
\end {array}$

The way to get line breaks in display math, while using only standard LaTeX, is to use \begin{array}...\end{array} within the display math environment $$...$$. (Yes, I know that $$ is deprecated but I still like it.) There are many alternatives in different extensions, including AMSLaTeX's align and align* environments. My personal favorite is Didier Rémy's mathpartir package, which gives a display-math environment that is more like paragraph mode, plus a set of tools for typesetting logical inference rules and proof trees.

Try something like this:

    \documentclass[varwidth,margin=3mm]{standalone}
    \usepackage{amsmath}
    \begin{document}
        \begin{math}
                \alpha(e1)=c1,\ \alpha(e2)=c3\\
                \alpha(e3)=c5,\ \alpha(e4)=c2\\
                \alpha(e5)=c4,\ \alpha(e1)=c1\\
        \end{math}
    \end{document}

The varwidth parameter is the key.
With it you can properly utilize \linebreak, \newline, \\, etc.
I used \begin{math} / \end{math}, but you should be able to use the old $ / $$ notation too.

You could use an eqnarray* instead.