# Incorrect horizontal spacing in cases mode

Consider the following MWE:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{align}
\begin{cases}
\mathrm{L}^{3a}\mathrm{L}^{2b}\mathrm{L}^{c}&=\mathrm{L}^1 \\
\mathrm{T}^{-2a}\mathrm{T}^{-b}\mathrm{T}^{-c}&=\mathrm{T}^0 \\
\mathrm{M}^{-a}\mathrm{M}^{b}&=\mathrm{M}^0
\end{cases}
\end{align}

$$\mathrm{T}^a=\mathrm{T}^1$$

\end{document}


which compiles to:

As can be seen, the spacing before the equal sign for the first system of equation is incorrect. It is instead correct the spacing in the second equation (I think).

How can I get the spacing in the system of equations (and in the second equation if it isn't already correct) right? By that, I mean maintaining all the equal signs one below another by having all equations left aligned and a correct spacing for the equal sign of the longest equation.

Thank you for your help, it is very appreciated.

• The motivation behind the spacing issue stems from the fact that the cases environment is set with 2 columns - the first column is for some expression while the second column is for a condition; something like f(x) <space> where x > 0. For this, the <space> is caused by the & and seems necessary. So, when you're using & as the regular "alignment character", you're using it incorrectly. – Werner Jan 11 '19 at 1:20

Is this what you want?

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\left\{ \begin{alignedat}{2} &\mathrm{L}^{3a} \mathrm{L}^{2b}\mathrm{L}^{c} &&=\mathrm{L}^1 \\ &\mathrm{T}^{-2a}\mathrm{T}^{-b}\mathrm{T}^{-c} &&=\mathrm{T}^0 \\ &\mathrm{M}^{-a} \mathrm{M}^{b} &&=\mathrm{M}^0 \end{alignedat} \right.
\end{document}

• Almost, I'd like the equations to be left aligned but by maintaining the equal signs on the same vertical line, thanks! – Edoardo Serra Jan 10 '19 at 23:49
• @EdoardoSerra, like this? – Sigur Jan 10 '19 at 23:50
• I'd prefer to still have the equal signs to be on the same vertical line – Edoardo Serra Jan 10 '19 at 23:53
• So you want equal signs one below others and the left side aligned to left?! They have different lengths so the spacing will not be the same. A gap will happens. – Sigur Jan 10 '19 at 23:54
• @EdoardoSerra, and now? – Sigur Jan 11 '19 at 0:01