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I am getting an error while using beamer that there is a missing }. I can't see where the error is since it compiles fine. Any help much appreciated.

    \begin{align}\label{gs_diff_homog_3}
\begin{bmatrix} \hat a(\omega, x_3) \\ \hat b(\omega,x_3) \end{bmatrix} &= \underbrace{\begin{bmatrix} \chi_1(\omega,x_3) & \chi_2(\omega,x_3) \\ \chi_3(\omega,x_3) & \chi_4(\omega,x_3) \end{bmatrix} \begin{bmatrix} \chi_1(\omega,0) & \chi_2(\omega,0) \\ \chi_3(\omega,0) & \chi_4(\omega,0) \end{bmatrix}^{-1}}_\textrm{$\mathbf{P_{\omega}}(0,x_3)$} \\ &\times\underbrace{\begin{bmatrix} \chi_1(\omega,0) & \chi_2(\omega,0) \\ \chi_3(\omega,0) & \chi_4(\omega,0) \end{bmatrix} \begin{bmatrix} c_1 \\ c_2 \end{bmatrix}}_\textrm{$[\hat a(\omega,0),\hat b(\omega,0)]^{T}$}. \nonumber
\end{align}

enter image description here

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  • What is the error message? Commented May 30, 2019 at 11:10
  • @AnonymousPhysicist ! Missing } inserted. <inserted text> Commented May 30, 2019 at 11:15
  • please always post a complete (small) test document that reproduces the error. Commented May 30, 2019 at 11:20
  • 1
    why are you using \textrm{$....$} in subscripts rather than using math mode directly???? Commented May 30, 2019 at 11:22

1 Answer 1

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subscripts should always be braced _{...} . (Don't rely on the fact that some font commands sometimes work unbraced.)

Here though, \textrm should not be used at all:

enter image description here

\documentclass{beamer}

\begin{document}

\begin{frame}{zzz}

    \begin{align}\label{gs_diff_homog_3}
\begin{bmatrix} \hat a(\omega, x_3) \\
 \hat b(\omega,x_3) \end{bmatrix} &= \underbrace{\begin{bmatrix} \chi_1(\omega,x_3) & \chi_2(\omega,x_3) \\
 \chi_3(\omega,x_3) & \chi_4(\omega,x_3) \end{bmatrix} \begin{bmatrix} \chi_1(\omega,0) & \chi_2(\omega,0) \\
 \chi_3(\omega,0) & \chi_4(\omega,0) \end{bmatrix}^{-1}}_{\mathbf{P_{\omega}}(0,x_3)} \\
 &\times\underbrace{\begin{bmatrix} \chi_1(\omega,0) & \chi_2(\omega,0) \\
 \chi_3(\omega,0) & \chi_4(\omega,0) \end{bmatrix} \begin{bmatrix} c_1 \\
 c_2 \end{bmatrix}}_{\hat a(\omega,0),\hat b(\omega,0)]^{T}}. \nonumber
\end{align}

\end{frame}

\end{document}

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