Question about the underbrace in combination with the array

Question

I'm trying to use the \underbrace option, and I kind of managed to make it work with the following code:

\begin{equation}
\begin{array}{rcl}
\left(\Lambda_1 \Lambda_2\right)^T G \left(\Lambda_1 \Lambda_2\right) =   &  \Lambda_2^T \underbrace{\Lambda_1^T G \Lambda_1} \Lambda_2 & = \Lambda_2^T G \Lambda_2 = G \\ 
 & = G & {}
\end{array} 
\end{equation}

However, I'm not really happy about the spacing between the different signs of the cells, because it is not how my other "normal" equations look like:

Does anybody know how I can make this look better?

Answer 1

In this particular instance, you don't need an array since it messes with the vertical alignment of your equation number. Instead, use \underbrace the way it's intended to be used:

\documentclass{article}
\begin{document}
\begin{equation}
  \begin{array}{rcl}
    \left(\Lambda_1 \Lambda_2\right)^T G \left(\Lambda_1 \Lambda_2\right) =  &  \Lambda_2^T \underbrace{\Lambda_1^T G \Lambda_1} \Lambda_2 & = \Lambda_2^T G \Lambda_2 = G \\ 
      & = G & {}
  \end{array} 
\end{equation}

\begin{equation}
  (\Lambda_1 \Lambda_2)^T G (\Lambda_1 \Lambda_2) = \Lambda_2^T \underbrace{\Lambda_1^T G \Lambda_1}_{{}=G} \Lambda_2 = \Lambda_2^T G \Lambda_2 = G
\end{equation}

\end{document}

If you wish to have a larger script in the \underbrace, use \textstyle.

If you must have some form of alignment, you could use a r@{}c@{}l column specification in your array and supplement the equations with surrounding empty groups {} to achieve proper spacing.