[OS X TeX] Using align with "or"

[David Arnold]

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

D.

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

D.


On Apr 17, 2011, at 12:56 PM, Bruno Voisin wrote:

> Le 17 avr. 2011 à 21:48, Lee D. Witt a écrit :
>> 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 & \quad\text{or}\quad  && u+4    &=0  & \quad\text{or}\quad  && u-4    &=0 \\
> u      &=0 &&&                       u      &=-4 &&&                       u      &=4 \\
> \log x &=0 &&&                       \log x &=-4 &&&                       \log x &=4
> \end{alignat}
> 
> Bruno
> 
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