# Why should I ever use equation when I can always use align? [duplicate]

Possible Duplicate:
align vs equation

Is there any reason why I should use equation when I align seems to produce the same output?

The reason I am asking is that I like solving math using LaTeX. Sometimes I write a single equation using the equation environment, but later realise I need to include more equations aligned to the first in that same environment. Then I need to change the



to

\begin{align}
\end{align}


and include the &s as appropriate.

I am thinking then: why not always use align, maybe even including the & before the equal sign, just in case I need to include more stuff there later? If they behave the same, and one is more flexible, why use the other at all? Or are there differences and reasons why I should avoid using align when there is a single equation?

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## marked as duplicate by cmhughes, Vivi, qubyte, percusse, lockstepMar 27 '12 at 5:17

Check the Short Math Guide for LaTeX it may help. –  adn Mar 27 '12 at 1:45
@cmhughes yes, it is a duplicate. Cheers :) –  Vivi Mar 27 '12 at 1:48

Say you want to split equations, then you need to use equation+split and align can't be used with split.

EDIT: This MWE shows why align can not be used to split an equation and split should be used.

\documentclass{article}
\usepackage{mathtools}
\begin{document}
%-------------------------------------------------
We use \verb|split| with \verb|\equation| environment to split this equation:
%=============================
$$\label{eq:grscope4} \begin{split} \Delta p_{x} &= \left[ {\left( {\frac{h}{\lambda }\sin \alpha } \right) - \left( { - \frac{h}{\lambda }\sin \alpha } \right)} \right] + \left( {\frac{h}{\lambda }\sin \alpha } \right)\\[4pt] & \phantom{==} - \left( {\frac{h}{\lambda }\sin \alpha } \right) \end{split}$$
%=============================
The number comes at the center of two equation.

We use \verb|align| to split the equation now:
%=============================
\begin{align}
\Delta p_{x} &= \left[ {\left( {\frac{h}{\lambda }\sin \alpha } \right)
- \left( { - \frac{h}{\lambda }\sin \alpha } \right)} \right]
+ \left( {\frac{h}{\lambda }\sin \alpha } \right)\\[4pt]
& \phantom{==} - \left( {\frac{h}{\lambda }\sin \alpha } \right)
\end{align}
%=============================
We get two numbers. To suppress one of them we say \verb|\nonumber|,
see the difference below:
%=============================
\begin{align}
\Delta p_{x} &=  \left[ {\left( {\frac{h}{\lambda }\sin \alpha } \right)
- \left( { - \frac{h}{\lambda }\sin \alpha } \right)} \right]
+ \left( {\frac{h}{\lambda }\sin \alpha } \right)\\[4pt]
& \phantom{==} - \left( {\frac{h}{\lambda }\sin \alpha } \right) \nonumber
\end{align}
%=============================
The \verb|\nonumber| is not effective in the first line where we wanted to suppress the number.
Instead it works in the last line only. Hence equation numbering becomes a mess.
%-------------------------------------------------
\end{document}


If the equation has to be split in more than two lines this situation worsens further if one is using align.

Conclusion equation can not be completely sacrificed for align.

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I had never heard of equation+split. I will look it up... –  Vivi Mar 27 '12 at 1:56
It seems to me the main issue is spacing. It makes a big difference to use equation instead of align, as explained in the duplicate question linked above. –  Vivi Mar 27 '12 at 2:03
@Vivi That is true. since it is discussed in the link, I did not mention. I will try to provide a MWE for split later today. –  Harish Kumar Mar 27 '12 at 2:10
@Vivi: The amsmath documentation has some nice examples on how to use split and other environments. I actually use it more than align these days, and you can use multiple splits in one equation, allowing some quite elaborate stuff. –  qubyte Mar 27 '12 at 3:01
@Vivi, See the MWE. –  Harish Kumar Mar 27 '12 at 4:27