Narrow the gap between align environment columns

[Dustinsfl]

\begin{align}
\tau = k_1e_0t, & u = \frac{s}{s_0}, & v_1 = \frac{c_1}{e_0}, & v_2 = \frac{c_2}{e_0},\notag\\
a_1 = \frac{k_{-1}}{k_1s_0}, & a_2 = \frac{k_2}{k_1s0}, & a_3 = \frac{k_3}{k_1}, & a_4 = \frac{k_{-3}}{k_1s_0},\notag\\
a_5 = \frac{k_4}{k_1s_0}, & \epsilon = \frac{e_0}{s_0}, & & \notag
\end{align}

How can I narrow the gap between the 2nd and 3rd items? The gap is a lot worse in a pdf compared to on the forum too.

 

[Evgeny.Makarov]

The standard way is to use two &'s for each column: one before = to align each column on equalities and one between columns. Thus, an environment with n column has 2n - 1 &'s in every line.

\begin{align*}
\tau &= k_1e_0t, & u &= \frac{s}{s_0}, & v_1 &= \frac{c_1}{e_0}, & v_2 &= \frac{c_2}{e_0},\notag\\
a_1 &= \frac{k_{-1}}{k_1s_0}, & a_2 &= \frac{k_2}{k_1s0}, & a_3 &= \frac{k_3}{k_1}, & a_4 &= \frac{k_{-3}}{k_1s_0},\notag\\
a_5 &= \frac{k_4}{k_1s_0}, & \epsilon &= \frac{e_0}{s_0}
\end{align*}

To control the spacing between columns, use the alignat environment, which accepts an argument specifying the number of columns. Then the spacing between columns is eliminated. You can therefore specify spacing explicitly using \quad, etc.

\begin{alignat*}{4}
\tau &= k_1e_0t, & u &= \frac{s}{s_0}, & v_1 &= \frac{c_1}{e_0}, & v_2 &= \frac{c_2}{e_0},\notag\\
a_1 &= \frac{k_{-1}}{k_1s_0}, &\quad a_2 &= \frac{k_2}{k_1s0}, &\quad a_3 &= \frac{k_3}{k_1}, &\quad a_4 &= \frac{k_{-3}}{k_1s_0},\notag\\
a_5 &= \frac{k_4}{k_1s_0}, & \epsilon &= \frac{e_0}{s_0}
\end{alignat*}

 

[Dustinsfl]

I like the alignat* feature.