Btukfyl

I find that I have unpleasant spacing between the equals sign and (e.g.) the exponential function in this particular case, while using the align environment. I have a long expression which has to be split up in multiple rows. The alignment character & appears to gobble up all space when it comes after the equals sign. How could I remedy this while still preserving the plus sign alignment below?

Ideally, I would like to have the second row from the first equation, and the first row from the second equation.

documentclass{article}

usepackage{amsmath}

begin{document}

begin{align} % bad spacing at first row, but correctly placed second row

    2 cosh t =& e^t \

            &+ e^{-t} 

end{align}

begin{align} % good spacing at first row, but incorrectly placed second row

    2cosh t &= e^t \

            &+ e^{-t} 

end{align}

end{document}

Put the ampersand before the equals sign. Then use quad to create the indentation in the second row.

documentclass{article}

usepackage{amsmath}

begin{document}

begin{align}                                                                   

    2 cosh t &= e^t \                                                         

              &quad+ e^{-t}                                                    

end{align}

end{document}

You can also use hspace if you want a different length for the indentation.

I wouldn't try aligning the plus with e^t, but if you insist, here's how.

documentclass{article}

usepackage{amsmath}

begin{document}



noindent

The plus is flush with $e^t$ (I wouldn't recommend it):

begin{align}

2cosh t ={}& e^t \

            & negmedspace+ e^{-t}

end{align}

The plus is moved right (better):

begin{align}

2cosh t &= e^t \

         &qquad+ e^{-t}

end{align}

end{document}

With negmedspace we kill the space at the left of the binary operation symbol.

However, align is the wrong tool here:

documentclass{article}

usepackage{amsmath}

begin{document}



begin{equation}

begin{split}

2cosh t &= e^t \

         &qquad + e^{-t}

end{split}

end{equation}

Suppose you wish to ensure that the two instances of e are aligned vertically, while respecting the fact that a binary operator (+) precedes the e in the second row. The most direct way to obtain this type of alignment is to use a pair of hphantom ("horizonal phantom") statements. The one in the first row mimics the + symbol (a binary operator) from the second row, and the hphantom statement in the second row mimics the = symbol (a relational operator) from the first row. The {} pairs are there to help TeX figure out which type of operator applies.

documentclass{article}

usepackage{amsmath}

setlengthtextwidth{3in} %% just for this example

begin{document}

begin{align}

    2cosh t &= phantom{{}+{}} mathrm{e}^t \

             &phantom{{}={}} + mathrm{e}^{-t}

end{align}

end{document} 

You have placed the & wrong; it should go before the equal sign to get the correct spacing. Also, I've used hphantom to indent the expression in the second line to get the correct alignment. (Notice the {} before =.)

documentclass{article}



usepackage{amsmath}



begin{document}



begin{align}

   2cosh t

   &= e^{t} \

   &hphantom{{}=} + e^{-t} 

end{align}



end{document}

Strictly speaking, only the first part of egreg's answer solves the problem as intended by Martin L. All other answers require space corrections of at least 1 or 2 mu. Here is an alternative.

LaTeX encloses relation symbols with thick spaces ;, and binary symbols with medium spaces :. The symbols = and + in our example are respectively of these kinds. Therefore, downgrading them to ordinary symbols, what we want is:

2 cosh t & ; mathord{=} ; e^t \

          & ; phantom{=} ; mathord{+} : e^{-t}

A practical incarnation of the above is (see page 36 of l2kurz.pdf):

2 cosh t & = e^{t} \

          & mathrel{phantom{=}} negmedspace {} + e^{-t}

First, we redeem the relation status of = robbed by the phantom command. Second, we insert an empty group {} telling LaTeX to interpret + as a binary rather than a prefix symbol; but this creates a spurious medium space : that needs to be compensated.