Underbrace equation issues

Question

I am trying to write this equation (see attached image)

But I have been unsuccessful. So far I have this :

\begin{equation}\label{eq23}
  {C_E}^* = 
  \underbrace{{\underbrace{1 - a_{C_E}}_{\centering\text{Basic viscous
  resistance}}} +
  {\underbrace{{k_{C_E}({v_S}^*-1)}}_{\centering\text{ Linear correction viscous resistance}}} + {\underbrace{c_{C_E}.\Big(e{^{d_{C_E}}.{v_s}^*} - e^d_{C_E}\Big)}_{\text{Non-linear viscous correction resistance}}}_{\text{Viscous resistance}}} +
  {\underbrace{a_{C_E}}.e^{b_{C_E}({v_s}^*-1)}_{\centering\text{Wavemaking resistance}}}
\end{equation}

Possible duplicate of Separate long math text under sum symbol into different lines? — , May 24 '19 at 09:05

score 6 · Answer 1 · answered May 24 '19 at 11:41

I'd define a specialized macro for this:

\documentclass{article}
\usepackage{geometry}
\usepackage{amsmath,mathtools}

\newcommand{\underlabel}[3][]{{%
  \underbrace{#2}_{#1{\mbox{\scriptsize\begin{tabular}{@{}c@{}}#3\end{tabular}}}}%
}}

\begin{document}

\begin{equation}\label{eq23}
{C_E}^* =
\underlabel{%
  \underlabel{1 - a_{C_E}}{Basic viscous \\ resistance} +
  \underlabel{k_{C_E}({v_S}^*-1)}{Linear correction \\ viscous resistance} +
  \underlabel{c_{C_E}(e{^{d_{C_E}}{v_s}^*} - e^d_{C_E})}
             {Non-linear viscous \\ correction resistance}
}{Viscous resistance} +
\underlabel[\mathclap]{a_{C_E}e^{b_{C_E}}({v_s}^*-1)}{Wavemaking resistance}
\end{equation}

\end{document}

A few stylistic remarks.

The period never denotes multiplication in math. You can use \cdot, but in this case no symbol is the tradition.

There's no need to enlarge the parentheses with \Big in this case. Even \big is superfluous. Remember, though, that you should use \Bigl before the left delimiter and \Bigr before the right delimiter.

loading amsmath doesn't harm, but with use of mathtools it is not needed :-) (+1 ) — Zarko, May 24 '19 at 12:26
I liked the larger parentheses enclosing the exponentiation. I guess there’s no one right way to typeset. — gen-ℤ ready to perish, May 24 '19 at 18:45
@ChaseRyanTaylor I see no problem in using \big size, if you so prefer, but \Big size is too much. I'd stick with standard size, though. — egreg, May 24 '19 at 20:16

Mico · Answer 2 · 2019-05-24T10:53:46.490

Some suggestions and observations

Use \substack{...\\...} directives to introduce linebreaks in the text passages below the under-braces.
Use \vphantom statements to align the three inner underbrace terms.
If needed, use \mathclap directives (provided by the mathtools package) let the underbrace material protrude to the left and right.
Use a (typographic) strut to align the "Viscous resistance" and "Wavemaking resistance" terms.

\documentclass{article}
\usepackage{mathtools}
\usepackage{newtxtext,newtxmath} % optional
\newcommand{\e}{\mathrm{e}} 
%% Create a typographic strut:
\newcommand{\mystrut}{\vphantom{% % use first term in summation
   \underbrace{1 - a_{\mathit{CE}}\big(}_{%
    \substack{\text{Basic viscous}\\\text{resistance}}}}}

\begin{document}
\begin{equation}\label{eq23}
  C_E^* =\underbrace{%
  \underbrace{1 - a_{\mathit{CE}}\vphantom{\big(}}_{%
    \substack{\text{Basic viscous}\\ 
              \text{resistance}}}
+ \underbrace{k_{\mathit{CE}}\bigl(v_s^*-1\bigr)}_{%
    \mathclap{\substack{\text{ Linear correction}\\ 
                        \text{viscous resistance}}}}
+ \underbrace{c_{\mathit{CE}}\cdot\bigl(
    \e^{d_{\mathit{CE}}\cdot v_s^*} - \e^{d_{\mathit{CE}}}\bigr)}_{%
    \substack{\text{Non-linear correction}\\ 
              \text{viscous resistance}}}}_{%
  \text{Viscous resistance}} 
+ \underbrace{a_{\mathit{CE}}\cdot
       \e^{b_{\mathit{CE}}\cdot(v_s^*-1)}\mystrut}_{%
       \mathclap{\text{Wavemaking resistance}}}
\end{equation}
\end{document}

Thanks a lot guys! This is really helpful – Nikhil May 25 '19 at 08:37 — Nikhil, May 25 '19 at 08:37

Underbrace equation issues

2 Answers2