How to stop centering effect when using split equation?

For example, the following code produces the equations below:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\begin{split} Helloworld & = A \\ & = B \end{split}$
\end{document}


I would like to know if it is possible to align left after using split equation

• Do you want all displayed equations to be left-aligned, or just the ones that feature a split environment?
– Mico
Aug 22 '15 at 6:08

amsmath provides the flalign environment. It is designed for placing two sets of aligned equations, the first block flush on the left margin, the second flush on the right, e.g.

\begin{flalign*}
x & = A & y &= B
\end{flalign*}


produces

|x = A                                       y = B|


The first and third & here provide aligment points for the two blocks, the middle & separates the blocks. The use of flalign* supresses equation numbers.

Placing your split in the first block, or simply before the first &, will thus make it align with the left margin.

\documentclass{article}

\usepackage{amsmath}

\begin{document}

Text before
\begin{flalign*}
\begin{split}
\textit{Helloworld} & = A \\
& = B
\end{split}&
\end{flalign*}
and after.
\begin{flalign*}
x & = A & y &= B \\
z & = C & u &= U
\end{flalign*}
Further text.

\end{document}

• Holy moly! That took me long to find this answer... Like hours!... More than two!... Thanks for sharing! :) For other desperate ones: this is the answer! Place the last & !after! \end{split}. Mar 2 '16 at 9:33

Environment multline could be misused to place the split to the left, because the first line of multline is left aligned with indent \multlinegap, which can be set to zero. Then split needs to be changed to aligned, because multline prefers the latter.

Example with a horizontal rule to show the text width:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\hrule
\setlength{\multlinegap}{0pt}
\begin{multline*}
\begin{aligned}
\text{Hello world} & = A\\
& = B
\end{aligned}\hfill
\end{multline*}
\hrule
\end{document}


Depending on the material to be set, a tabular or similar might be an alternative.