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I'm trying to use the equation tag on the following portion of formula: enter image description here

I did it as well:

\begin{equation}
\centerline{$
\min _{w, b, \xi_{i}} \frac{\|w\|^{2}}{2}+C \sum_{i=1}^{n} \xi_{i}
$} 

subject to:

\centerline{$
\begin{aligned}
y_{i}\left(w^{T} \phi\left(x_{i}\right)+b\right) \geq 1-\xi_{i} & & \text { for all } i=1, \ldots, n \\
\xi_{i} \geq 0 & & \text { for all } i=1, \ldots, n
\end{aligned}$}
\end{equation}

but when I run it I get the following error:

1 - Missing $ inserted.

2 - Display math should end with $$.

3 - Bad math environment delimiter.

2
  • 1
    Welcome to TSE. Please post a Minimal Working Example, instead of a code snippet. Sep 28, 2021 at 13:16
  • 3
    `\centerline shouldn't really be used in latex and certainly not in or around equations. you can also not have blank lines in equations. Sep 28, 2021 at 13:17

1 Answer 1

5

Like this?:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{gather}
\min _{w, b, \xi_{i}} \frac{\|w\|^{2}}{2}+C \sum_{i=1}^{n} \xi_{i}
\shortintertext{subject to:}
\begin{aligned}
y_{i}\left(w^{T} \phi\left(x_{i}\right)+b\right) \geq 1-\xi_{i} & & \text { for all } i=1, \ldots, n \\
\xi_{i} \geq 0 & & \text { for all } i=1, \ldots, n
\end{aligned}
\end{gather}
\end{document}

enter image description here


Edit: As Sebastiano suggest in a comment this optimization problems should be written with optidef package:

\documentclass{article}
\usepackage{optidef}
\begin{document}
\begin{mini}
{w, b, \xi_{i}}{\frac{\|w\|^{2}}{2}+C \sum_{i=1}^{n} \xi_{i}}{}{}
\addConstraint{y_{i}\left(w^{T} \phi\left(x_{i}\right)+b\right)}{\geq 1-\xi_{i}\quad}{\text {for all } i=1, \ldots, n}
\addConstraint{\xi_{i}}{\geq 0}{\text {for all } i=1, \ldots, n}
\end{mini}
\end{document}

enter image description here

The package has many environments and many alternatives to display this optimization problem. It also has some aligning points, that I have used in the example

4
  • 1
    +1 surely. I think that the optidef package It seems Better.
    – Sebastiano
    Sep 28, 2021 at 22:13
  • 1
    I will see optidef package, thanks for the suggestion! Sep 28, 2021 at 22:52
  • Very very good. It Is very nice. I had upvoted Yesterday.
    – Sebastiano
    Sep 29, 2021 at 14:23
  • 1
    Thank you for letting me know about optidef package Sep 29, 2021 at 16:01

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