[Tex/LaTex] Use flalign or alignat or align or similar environment to align to the left

Question

The following is a small example to use flalign environment to generate equation.

\documentclass{article}
\usepackage{amsmath}
\usepackage{txfonts}

\begin{document}
The formula is:
\begin{flalign*}
  \lambdaup &= \lambdaup_1 + \lambdaup_2\\
\end{flalign*}

\end{document}

The output aligns at the center:

The formula is
                  lambda = lambda_1 + lambda_2

How can I make the alignment to the left, using flalign, alignat or align environment? I mean:

The formula is
lambda = lambda_1 + lambda_2

According to Michael's comment, adding option [fleqn] to package amsmath and setting \mathindent=0.0pt will solve the problem. But this will make all equations align to the left. How can I make the function locally to some environment instead of the whole article?

Answer 1

You can use Flalign instead.

The formula is
\begin{flalign*}
a &= b+c &\\
  &= 1+1 &\\
  &= 2  &
\end{flalign*}