# [OS X TeX] Using align with "or"

Ross Moore ross.moore at mq.edu.au
Mon Apr 18 00:47:22 CEST 2011

Hi David,

On 18/04/2011, at 8:35 AM, David Arnold wrote:

> Bruno et al,
>
> This is precisely what I needed. But now I think I also need an explanation. We have:
>
> \begin{alignat}{5}
>
> But the first row has 9 ampersands. I've stumbled into solutions like this on my own, but I just don't understand the use of the ampersands.

Lee Witt said:

>>>  If you want to align n columns use 2n-1 &s

The point is that the alignment at each ampersand alternates:
right alignment, then left alignment.

So if you have columns each with an alignment point "inside" the content,
then you need "&&" between the columns,

viz.

A&=B   &&   C&=D   && ...

> Is this use of the ampersands explained in any documentation?

Try  The LaTeX Companion    1st or 2nd editions.

>
> D.
>
> P.S. Also, is there any way to spread out the output a bit?

try the variants:

\begin{xalignat}{5}
....

or

\begin{xxalignat}{5}
....

and use  {alignat*}  {xalignat*}  if you don't want equation numbers.
{xxalignat} suppresses them anyway.

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>
>
> D.
>
>
> On Apr 17, 2011, at 12:56 PM, Bruno Voisin wrote:
>
>> Le 17 avr. 2011 ? 21:48, Lee D. Witt a ?crit :
>>> Have you tried "alignat"? You specify the number of "columns" to align. If you want to align n columns use 2n-1 &s
>>>
>> \begin{alignat}{5}
>> u      &=0 &&&                       u      &=-4 &&&                       u      &=4 \\
>> \log x &=0 &&&                       \log x &=-4 &&&                       \log x &=4
>> \end{alignat}
>>
>> Bruno

Hope this helps,

Ross

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