What is the best way to align equal signs and sum symbols in the following MWE?

```
\documentclass[a4paper]{report}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{alignedat}{4}
y_\text{L} = & \sum_{s=1}^n \left( Y_s \, \lambda_s \right) & \quad &
\\
x = & \sum_{s=1}^n \left( X_s \, \lambda_s \right) & \quad & x \geq 0
\\
& \sum_{s=1}^n \lambda_s = 1 & \quad & \lambda_s \geq 0
\end{alignedat}
\end{equation}
\end{document}
```

This is not perfect but works. As far as I know `&=`

should be preferred over `=&`

since the latter causes the space shrieked. But I cannot achieve desired alignment with `&=`

.

## Best Answer

Please clarify what exactly you want to achieve! Here is your code how I would have written it:

You may decide if you want to have the last or the previous line.

Please note that the use of

`\left(`

and`\right)`

is not needed here and does change the spacing. For this very case,`\sum_{s=1}^nY_s\lambda_s`

would be enough to be understood right.If you like, you may write

`x_{\phantom{s}}\geq 0`

in order to get the inequalities aligned as well.