2

From other sources (e.g. here and here), I have cobbled together an equation with underbraces labelling each part.

I would like to add an underbrace to this part:

\rm{tanh}(W_2x_t + U_2h_{t-1} + b_2)

but whenever I do, I get an error: Missing $ inserted.

In the comments in the MWE below, I include the code I tried that generated the error.

How can I add an underbrace to that part of the equation - it's multiplied by a term that already has an underbrace, if that's a problem?

\documentclass{article}
\usepackage{mathtools}% Loads amsmath
\begin{document}
\[
c_t = 
    \underbrace{\sigma(W_3 x_t + U_3h_{t-1} + b_3)}_\text{forget gate} c_{t-1} +
    \underbrace{\sigma(W_1x_t + U_1h_{t-1} + b_1)}_\text{input gate} \rm{tanh}(W_2x_t + U_2h_{t-1} + b_2)
\]
\end{document}

%\[
%  c_t = 
%    \underbrace{\sigma(W_3 x_t + U_3h_{t-1} + b_3)}_\text{forget gate} c_{t-1} + 
%    \underbrace{\sigma(W_1x_t + U_1h_{t-1} + b_1)}_\text{input gate} \underbrace{\rm{tanh}(W_2x_t + U_2h_{t-1} + b_2)}_\text{c_{new_t}}
%\]
StatsSorceress
  • 448

1 Answers1

3

Well, \text expects its argument to be text. I.e. inside its argument you are not in math mode anymore and must add $…$ to get the text in math mode. However since you don’t want text at all, don’t use the macro and write \underbrace{…}_{c_{new_t}}.

You may also like to improve your code further:

  1. Use \tanhinstead of using a deprecated font macro (\rm). (If you need other operators, they should be defined with\DeclareMathOperator{\tanh}{tanh}` for example.
  2. Use \text, where it is necessary, e.g. in c_{\text{new}_t}
\documentclass{article}
\usepackage{mathtools}% Loads amsmath

%\DeclareMathOperator{\tanh}{tanh}% already defined in that way …

\begin{document}
\[
c_t = 
    \underbrace{\sigma(W_3 x_t + U_3h_{t-1} + b_3)}_\text{forget gate} c_{t-1} +
    \underbrace{\sigma(W_1x_t + U_1h_{t-1} + b_1)}_\text{input gate} \underbrace{\tanh(W_2x_t + U_2h_{t-1} + b_2)}_{c_{\text{new}_t}}
\]
\end{document}
Tobi
  • 56,353