# How to ensure horizontal alignment when using overbrace function and split equations?

Happy lockdown. I am currently trying to align three split equations together while using the overbrace function to describe the functions of each section (they are symmetrical but for co-ordinate direction). The current code I have is:

\begin{align}
\label{eqn:mom2}
\begin{split}
&x : \overbrace{\rho \frac{Du}{Dt}}^\text{Convection} = \overbrace{\rho g_x - \frac{\delta p}{\delta x} }^\text{Pressure} + \overbrace{\mu (\frac{\delta^2 u}{\delta x^2} + \frac{\delta^2 u}{\delta y^2} + \frac{\delta^2 u}{\delta z^2}) }^\text{Diffusion}
\\
&y : \rho \frac{Dv}{Dt} = \rho g_y - \frac{\delta p}{\delta y} + \mu (\frac{\delta^2 v}{\delta x^2} + \frac{\delta^2 v}{\delta y^2} + \frac{\delta^2 v}{\delta z^2})
\\
&z : \rho \frac{Dw}{Dt} = \rho g_z - \frac{\delta p}{\delta z} + \mu (\frac{\delta^2 w}{\delta x^2} + \frac{\delta^2 w}{\delta y^2} + \frac{\delta^2 w}{\delta z^2})
\end{split}
\end{align}


If you see the attached, the presence of the overbracket misaligns the first equation line with the other two.

Would appreciate any help massively, causing a big headache!!

Josh

• Welcome to TeX.SE.
– Mico
Mar 29, 2020 at 16:22
• I also advise you to fix the round brackets that are too small :-)....and to put a complete code with the packages. Welcome again. Mar 29, 2020 at 16:29
• @Sebastiano - I've updated my answer to incorporte your suggestion. :-)
– Mico
Mar 29, 2020 at 16:32

You were very close! I suggest you encase \text{Convection} in a \mathclap directive, effectively making it have zero width. Separately, I would increase the size of the parentheses in the "diffusion" block.
\documentclass{article}
$$\label{eqn:mom2} \begin{split} x :\quad {\overbrace{\rho \frac{Du}{Dt}}^{\mathclap{\text{Convection}}}} &= {\overbrace{\rho g_x - \frac{\delta p}{\delta x} }^{\text{Pressure}}} + {\overbrace{\mu \Bigl(\frac{\delta^2 u}{\delta x^2} + \frac{\delta^2 u}{\delta y^2} + \frac{\delta^2 u}{\delta z^2}\Bigr)\phantom{x} }^{\text{Diffusion}}} \\ y :\quad \rho \frac{Dv}{Dt} &= \rho g_y - \frac{\delta p}{\delta y} + \mu \Bigl(\frac{\delta^2 v}{\delta x^2} + \frac{\delta^2 v}{\delta y^2} + \frac{\delta^2 v}{\delta z^2}\Bigr) \\ z :\quad \rho \frac{Dw}{Dt} &= \rho g_z - \frac{\delta p}{\delta z} + \mu \Bigl(\frac{\delta^2 w}{\delta x^2} + \frac{\delta^2 w}{\delta y^2} + \frac{\delta^2 w}{\delta z^2}\Bigr) \end{split}$$