# Vertical spacing problem with align and split environments

I'm having a vertical spacing problem when I show four equations, in two columns. This MWE shows the problem:

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}

\begin{document}

\begin{align}
\nabla \cdot \vec{E} &= 0,
&\nabla \times \vec{E} &= -\: \frac{\partial \vec{B}}{\partial t}, \\
\nabla \cdot \vec{B} &= 0,
&\nabla \times \vec{B} &= +\: \frac{\partial \vec{E}}{\partial t}.
\end{align}
Blablabla bla bla blabla:
\begin{align}
\begin{split}
\nabla \cdot \vec{E} &= 0, \\
\nabla \cdot \vec{B} &= 0,
\end{split}
&
\begin{split}
\nabla \times \vec{E} &= -\: \frac{\partial \vec{B}}{\partial t}, \\
\nabla \times \vec{B} &= +\: \frac{\partial \vec{E}}{\partial t}.
\end{split}
\end{align}

\end{document}


The first set of equations is perfect, but I need a single tag number for the whole set, instead of two tag numbers. So I used the split environment for a second set of identical equations.

Preview with the problem shown in red:

What am I doing wrong? How can I make the vertical spacing exactly the same for the two columns? Is there a way to do this without adding a \vphantom part?

• The \: commands should be removed. Mar 14 '20 at 20:57
• @egreg, why? Without them, there's not enough space between - and the fraction.
– Cham
Mar 14 '20 at 20:58
• Which is the normally used way. Mar 14 '20 at 20:59
• @egreg, well I always found this very ugly, and not clear enough. I believe there should be a bit more space there, so that's why I use \:.
– Cham
Mar 14 '20 at 21:00

\documentclass[11pt,letterpaper,twoside]{book}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{mathtools}

\begin{document}

\begin{align}
\nabla \cdot \vec{E} &= 0,
&\nabla \times \vec{E} &= -\: \frac{\partial \vec{B}}{\partial t}, \\
\nabla \cdot \vec{B} &= 0,
&\nabla \times \vec{B} &= +\: \frac{\partial \vec{E}}{\partial t}.
\end{align}

Blablabla bla bla blabla:
\begin{alignedat}{2} \nabla \cdot \vec{E} &= 0,\qquad&\nabla \times \vec{E} &= -\: \frac{\partial \vec{B}}{\partial t}, \\[\jot] \nabla \cdot \vec{B} &= 0,&\nabla \times \vec{B} &= +\: \frac{\partial \vec{E}}{\partial t}. \end{alignedat}

\end{document}

• Well, now the horizontal spacing is too small.
– Cham
Mar 14 '20 at 20:34
• @Cham, instead of qquad use \hspace{5em} ... Mar 14 '20 at 20:35
• @Zarko or 100cm is even bigger Mar 14 '20 at 20:38
• Why use alignedat? Why not just aligned? Mar 14 '20 at 21:07