Problem using aligned

Question

This MWE
documentclass{article}

usepackage{amsmath}

begin{document}
    
    $$begin{aligned}
        Gamma_{11}^1  & =0, qquad Gamma_{12}^1  & =0, qquad Gamma_{22}^1  & =-frac{1}{2}G_u, 
        GGamma_{11}^2 & =0, qquad GGamma_{12}^2 & =frac{1}{2}G_u, qquad GGamma_{22}^2 & =0. 
    end{aligned}$$
    
end{document}

Generates: 
and I can't understand why is the middle & not working, I've used it in the same way as the first and last &.

Jasper Habicht · Accepted Answer

Since it seems to be a common question how to correctly place ampersands in alignment environments in math, maybe it helps to illustrate it like this:
In a lot of alignment environments for math (for example align, aligned, alignat etc.), each ampersand introduces a new column and each double backslash introduces a new row. In each row, every first column is right-aligned and every second column is left-aligned.
documentclass[varwidth]{standalone}

usepackage{amsmath}

begin{document}footnotesize

[begin{aligned}
        fbox{onestrut} & fbox{twostrut} 
        fbox{right-alignedstrut} & fbox{left-alignedstrut} 
    end{aligned}]
    
    bigskip
    
    [begin{aligned}
        fbox{onestrut} & fbox{twostrut} & fbox{threestrut} & fbox{fourstrut} & fbox{fivestrut} & fbox{sixstrut} 
        fbox{right-alignedstrut} & fbox{left-alignedstrut} & fbox{right-alignedstrut} & fbox{left-alignedstrut} & fbox{right-alignedstrut} & fbox{left-alignedstrut} 
    end{aligned}]

bigskip
    
    [begin{aligned}
        fbox{onestrut} & fbox{twostrut} & fbox{threestrut} & fbox{fourstrut} & fbox{fivestrut} & fbox{sixstrut} 
        Gamma_{11}^1  & =0, &qquad Gamma_{12}^1  & =0, &qquad Gamma_{22}^1  & =-frac{1}{2}G_u, 
        GGamma_{11}^2 & =0, & GGamma_{12}^2 & =frac{1}{2}G_u, & GGamma_{22}^2 & =0. 
    end{aligned}]
    
end{document}

Mico · Answer

I suggest you switch to an alignedat environment and place the qquad directives on the second line. I would also use tfrac rather than frac, in order to reduce the visual prominence of the fraction terms.

documentclass{article}
usepackage{amsmath}
begin{document}
[
begin{alignedat}{3}
  Gamma_{!11}^1 &=0,       &  Gamma_{!12}^1 &=0,                      &  Gamma_{!22}^1  &=-tfrac{1}{2}G_u, 
 GGamma_{!11}^2 &=0,qquad & GGamma_{!12}^2 &=tfrac{1}{2}G_u, qquad & GGamma_{!22}^2  &=0 ,. 
end{alignedat}
]  
end{document}

Or, use a single alignat* environment instead of the [ begin{alignedat}{3} ... end{alignedat} ] combination:
begin{alignat*}{3}
  Gamma_{!11}^1 &=0,       &  Gamma_{!12}^1 &=0,                      &  Gamma_{!22}^1  &=-tfrac{1}{2}G_u, 
 GGamma_{!11}^2 &=0,qquad & GGamma_{!12}^2 &=tfrac{1}{2}G_u, qquad & GGamma_{!22}^2  &=0 ,. 
end{alignat*}

Problem using aligned

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