[Tex/LaTex] Left-align a split equation

alignamsmathmath-mode

I am trying to left-justify a split equation. I would like to have the first line left-justified, and have a hanging indent on the second line. I used flalign successfully for other equations that weren't split, but this split equation is causing me problems. Any suggestions are much appreciated!

\documentclass{article}
\usepackage{amssymb}
\usepackage{amsmath}
\begin{document}
\begin{flalign}
\begin{split}
\Lambda^{12}_{ee}&=\Lambda^{21}_{ee}=\frac{64x_e}{75k_B}\sqrt{\frac{m_e}{2\pi k_BT_e}}\left[\sum_{j\in\set{H}}x_j\left(\frac{175}{16}\Omega^{(1,1)}_{ej}-\frac{315}{8}\Omega^{(1,2)}_{ej}+57\Omega^{(1,3)}_{ej} -30\Omega^{(1,4)}_{ej} \right)\right. \\ 
&\left.+x_e\sqrt{2}\left(\frac{7}{4}\Omega^{(2,2)}_{ee}-2\Omega^{(2,3)}_{ee}\right)\right] 
\end{split}
\end{flalign}

\end{document}

Best Answer

I'm not sure to understand what you mean by “left aligning”; either you left align or center all equations.

For the specific case, the formula is really difficult to split sensibly, so I propose a different strategy:

\documentclass{article}

\usepackage{amsmath}
\usepackage{amssymb}

\newcommand{\set}[1]{#1}%??? The definition was missing

\begin{document}
\begin{equation}
\begin{split}
\Lambda^{12}_{ee}&=
  \Lambda^{21}_{ee}=\frac{64x_e}{75k_B}\sqrt{\frac{m_e}{2\pi k_BT_e}}\,
  \biggl(\,\sum_{j\in\set{H}}x_jA_{ej}+x_e\sqrt{2}\,B_{e}\biggr)\\
A_{ej}&=\frac{175}{16}\Omega^{(1,1)}_{ej}-
        \frac{315}{8}\Omega^{(1,2)}_{ej}+
        57\Omega^{(1,3)}_{ej}-
        30\Omega^{(1,4)}_{ej} \\[1ex]
B_{e}&=\frac{7}{4}\Omega^{(2,2)}_{ee}-2\Omega^{(2,3)}_{ee}
\end{split}
\end{equation}

\end{document}

enter image description here