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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

\begin{equation}
\end{equation}

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, lockstep Mar 27 '12 at 5:17

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1  
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
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1 Answer 1

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:
%=============================
\begin{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}
\end{equation}
%=============================
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}

enter image description here

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
2  
@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
1  
@Vivi, See the MWE. –  Harish Kumar Mar 27 '12 at 4:27
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