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}

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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.