# How to create newlines?

I am new to Latex and found out how to use it a bit. Newlines are created by \\

I get the following error: \\ can only appear in a matrix or array

How do you create newlines between matrix or arrays?

Thanks

EDIT: Here's the code. This is for an online forum that processes LaTeX.

a =
\left[
\begin {array}{ccc}
1& 2&3\\
\noalign{\medskip}
4&5&6
\end {array}
\right]

b = a .+ 1

b =
\left[
\begin {array}{ccc}
2&3&4\\
\noalign{\medskip}
5&6&7
\end {array}
\right]


By the way, what is the proper etiquette to post the code? Do I need code tags? Or LaTeX tags? Thanks.

-
Would you please show an example of what you are trying to achieve? –  egreg Oct 29 '11 at 15:03
Welcome to TeX.sx! A tip: If you indent lines by 4 spaces or enclose words in backticks , they'll be marked as code, as can be seen in @Alan's edit. You can also highlight the code and click the "code" button (with "{}" on it). –  Werner Oct 29 '11 at 15:26
You can format code by selecting the text and clicking on the {} icon. It's also helpful to post complete minimal working examples (MWE). –  Alan Munn Oct 29 '11 at 15:27
I didn't know if I should also show it as formatted in LaTeX. How would you do that? I checked the FAQ but I didn't see anything about it. –  B Seven Oct 29 '11 at 15:41

Load the amsmath package (\usepackage{amsmath}); then

\begin{align*}
a &=
\begin{bmatrix}
1& 2&3\\
4&5&6
\end{bmatrix}
\\
b &= a \mathbin{.+} 1
\\
b &=
\begin{bmatrix}
2&3&4\\
5&6&7
\end{bmatrix}
\end{align*}


will print the three formulas in different lines.

The code \noalign{\medskip} works, but it's more practical to write

\\medskipamount]  instead of \\ \noalign{\medskip}  - Without knowing the full details of the forum that you're posting on, it's hard to be 100% sure. However, it appears that you have not told the forum to process your code in Math Mode. There are a variety of ways that you can enter Math Mode, including • ... • \[ ...
• $$...$$
• \begin{equation*}...\end{equation*}

but the forum you mention may not support all of these. Presumably it will support at least the first two.

A good approach might be to compile your code locally before posting to the forum to make sure that you know what you want it look like- this will help you to narrow down if it's the forum that is not processing your code correctly, or if you have incorrect code. A MWE example follows of what your code might look like in a document.

\documentclass{article}

\begin{document}

\begin{array}{ll} a & = \left[ \begin {array}{ccc} 1& 2&3\\ \noalign{\medskip} 4&5&6 \end {array} \right]\\ \noalign{\medskip} b & = a .+ 1 \\ \noalign{\medskip} & = \left[ \begin {array}{ccc} 2&3&4\\ \noalign{\medskip} 5&6&7 \end {array} \right] \end{array}

\end{document}
`
-
Sorry, I omitted the  or [itex] tags. –  B Seven Oct 29 '11 at 16:22