[Tex/LaTex] Latex does not go to next line

indentationmath-mode

I am working on a document for school, trying to make some equations lines. However, the double dollar command for making equations omits the next line command.

$$
    S(k+1)  &= \sum(a[i]\cdot a[j] \mid i,j : 0\leq i\leq j < k + 1)\\
            &=
$$

I would expect the equation to go to the next line and continue indentation from the = character, however the document shows me this:

I have tried disabling packages but this offers no solution.

When I started working in this document there were no issues, a few hours later it suddenly stopped working correctly.

Any help is very much appreciated.

Best Answer

This cannot work: the construct $$ ····· $$ (which anyway is a plain TeX construction and should be replaced in LaTeX with \[ ····· \]) is for a one-line centred equation.

For what you want you should use the amsmath align (lines numbered) or align*(unnumbered), with the alignment point specified with an ampersand. For other types of multiline equations, please take a look at the documentation of amsmath, or its extension mathtools.

Related Solutions

[Tex/LaTex] LaTeX symbol for “does not divide”

Try this:

$x\nmid y$

It has been known to 'save the day'.

[Tex/LaTex] indent the next line by an exactly specified position

Most TeX compilers provide the feature \pdfsavepos that allows to record the position on the shipout page. It was introduced in pdfTeX and is nowadays available in pdfTeX, both modes DVI and PDF, XeTeX, and LuaTeX.

Because the position is not known, before the page is output, some kind of reference system is needed. Package zref-savepos of project zref provides an interface to the \pdfsavepos feature.

\documentclass{article}
\usepackage{zref-savepos}
\makeatletter
% \zsaveposx is defined since 2011/12/05 v2.23 of zref-savepos
\@ifundefined{zsaveposx}{\let\zsaveposx\zsavepos}{}
\makeatother
\newcounter{hposcnt}
\renewcommand*{\thehposcnt}{hpos\number\value{hposcnt}}
\newcommand*{\SP}{% set position
  \stepcounter{hposcnt}%
  \zsaveposx{\thehposcnt s}%
}
\makeatletter
\newcommand*{\UP}{% use previous position
  \zsaveposx{\thehposcnt u}%
  \zref@refused{\thehposcnt s}%
  \zref@refused{\thehposcnt u}%
  \kern\zposx{\thehposcnt s}sp\relax
  \kern-\zposx{\thehposcnt u}sp\relax
}
\makeatother

\begin{document}

This \SP is the first line\\
     \UP One more \SP line\\
                  \UP And another.

\end{document}

Some remarks:

The label names are automatically chosen via the help of a counter. That makes the usage easier, because the user don't need to invent unique label names.
The internal position data are integer numbers with implicit unit sp.
\zref@refused marks the reference as used to allow LaTeX the notification for undefined references.

Best Answer

Related Solutions

[Tex/LaTex] LaTeX symbol for “does not divide”

[Tex/LaTex] indent the next line by an exactly specified position

Related Question