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I had some problems while trying to align some equations in an align* environment. The output should be something like this:

As you can see, all the + symbols are vertically aligned, and so are the letters after them. I tried with an align* environment to get a similar result, but I was not able to align the symbols nor the letters. Here is my code and output:

begin{align*}

a &+2alpha az &+3alpha^2 az^2 &+4alpha^3az^3 &+5alpha^4az^4 +mbox{ecc.}\

&+bz &+2alpha bz^2 &+3alpha^2 bz^3 &+4alpha^4bz^4,

end{align*}

Is there a manner to get a more elegant result, without all those white spaces inside the sums? Thank you!

I don't think you want centering, but rather that the powers of z are aligned to each other.

In order to avoid to type &+{}& for each addition symbol, I define a handy shortcut.

documentclass{article}

usepackage{amsmath}



begin{document}



With all variables spelled out

begin{equation*}

begingrouplccode`~=`+ lowercase{endgroupedef~}{&mathcharthemathcode`+{}&}

mathcode`+=string"8000

begin{alignedat}{6}

a + 2alpha az + 3alpha^2 az^2 + 4alpha^3 az^3 + 5alpha^4 az^4 + text{ecc.}\

  +         bz + 2alpha   bz^2 + 3alpha^2 bz^3 + 4alpha^4 bz^4 &,

end{alignedat}

end{equation*}

and like the original

begin{equation*}

begingrouplccode`~=`+ lowercase{endgroupedef~}{&mathcharthemathcode`+{}&}

mathcode`+=string"8000

begingrouplccode`~=`* lowercase{endgroupdef~}#1{hphantom{#1}}

mathcode`*=string"8000

begin{alignedat}{6}

a + 2alpha az + 3alpha^2 az^2 + 4alpha^3 az^3 + 5alpha^4 az^4 + text{etc.,}\

  +         b*{z} + 2alpha   b*{z^2} + 3alpha^2 b*{z^3} + 4alpha^4 b*{z^4}

end{alignedat}

end{equation*}



end{document}

align gives alternating left and right alignment, but here I think you want centering so

documentclass{article}



usepackage{array,amsmath}



begin{document}



[

  begin{array}{*{20}{@{}>{{}}c<{{}}@{}}}

a &+&2alpha az &+&3alpha^2 az^2 &+&4alpha^3az^3 &+&5alpha^4az^4 &+&mbox{ecc.}\

&+&bz &+&2alpha bz^2 &+&3alpha^2 bz^3 &+&4alpha^4bz^4,

  end{array}

]

end{document}

Here is a way with the alignat* environment and the eqparbox package:

documentclass{article}



usepackage{mathtools, eqparbox}

newcommand{eqmathbox}[2][T]{eqmakebox[#1]{$displaystyle#2$}}



begin{document}



begin{alignat*}{4}

a &+eqmathbox{2alpha az} & & +eqmathbox[T2]{3alpha^2 az^2}& & + eqmathbox[T3]{4alpha^3az^3} & & +eqmathbox[T4]{5alpha^4az^4} +mbox{&c.}\

&+eqmathbox{bz} & & +eqmathbox[T2]{2alpha bz^2} & & +eqmathbox[T3]{3alpha^2 bz^3} & & +eqmathbox[T4]{4alpha^4bz^4},

end{alignat*}



end{document} 

The same array thing but simpler and right aligned. I use setlength{arraycolsep}{0pt} to keep the natural spacing of the binary operator +.

documentclass[a4paper]{article}

usepackage{amsmath,array}



begin{document}



[setlength{arraycolsep}{0pt}

begin{array}{*6{>{{}}r<{{}}}}

a +& 2alpha az +& 3alpha^2 az^2 +& 4alpha^3az^3  +& 5alpha^4az^4 +& mbox{ecc.},\

  +& bz         +& 2alpha bz^2   +& 3alpha^2 bz^3 +& 4alpha^4bz^4 phantom{{}+{}}&

end{array}

]



end{document}