# Reduce spacing between subequations

How can I reduce Spacing of the following subequations:

$\begin{subequations} $$x_{n+1}= x_n + v_n \Delta t + \frac{1}{2} a_n \Delta t^2$$ $$v\left(t_n+\Delta t/2\right)= v_n + \frac{1}{2}a_n \Delta t$$ $$a_{n+1}=\frac{1}{m} F(x_{x+1},t_{n+1})$$ $$v_{n+1}=v(t_n+\Delta t/2) + \frac{1}{2}a_{n+1}\Delta t$$ \end{subequations}$


I do not know how to embed the code here correctly.

• (1) welcome, (2) please provide a full minimal example that can be copied and tested as is without having to add anything. (3) You definitely do not want that $...$, (4) the extra spacing is because you are using separate equation envs after each other. If there is a common alignment , use align to house all four lines, or if not, use gather Sep 1, 2016 at 9:49

As @daleif said, do not use separate equation environments, but the multiline (not multline!) environment gather if all equations have to be centred. In addition,the fraction coefficient are a little too big here, in my opinion.. You can use \mfrac (medium-sized fractions, ~ 80 % of \displaystyle) from nccmath to reduce spacing further:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath, nccmath}
\usepackage[french]{babel}

\begin{document}

\begin{subequations}
$$x_{n+1}= x_n + v_n Δt + \frac{1}{2} a_n Δt²$$
$$v\left(t_n+Δt/2\right)= v_n + \frac{1}{2}a_n Δt$$
$$a_{n+1}=\frac{1}{m} F(x_{x+1},t_{n+1})$$
$$v_{n+1}=v(t_n+Δt/2) + \frac{1}{2}a_{n+1}Δt$$
\end{subequations}

\bigskip

\begin{subequations}
\begin{gather}
x_{n+1}= x_n + v_n Δt + \mfrac{1}{2} a_n Δt²\\
v\left(t_n+Δt/2\right)= v_n + \mfrac{1}{2}a_n Δt\\
a_{n+1}=\mfrac{1}{m} F(x_{x+1},t_{n+1})\\
v_{n+1}=v(t_n+Δt/2) + \mfrac{1}{2}a_{n+1}Δt
\end{gather}
\end{subequations}
\end{document}


• why not just even \tfrac? I still find them a bit large Sep 1, 2016 at 10:29
• For me, sizes are too different. I don't like this discrepancy. Of course, that's a matter of taste… Sep 1, 2016 at 10:32

I'd also suggest using align inside subequations to remove the extra spacing between separate equation environments. Using nccmath is also a good idea as @Bernard pointed out.

\documentclass{article}
\usepackage{mathtools,nccmath}
\begin{document}

\begin{subequations}
\begin{align}
x_{n+1}&= x_n + v_n \Delta t + \mfrac{1}{2} a_n \Delta t^2\\
v\left(t_n+\Delta t/2\right)&= v_n + \mfrac{1}{2}a_n \Delta t\\
a_{n+1}&=\mfrac{1}{m} F(x_{x+1},t_{n+1})\\
v_{n+1}&=v(t_n+\Delta t/2) + \mfrac{1}{2}a_{n+1}\Delta t
\end{align}
\end{subequations}

\end{document}