Aligning equation numbers inside and outside of an algorithm

Question

\documentclass[12pt, a4paper]{report}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage[ruled]{algorithm2e}

\begin{document}

\begin{algorithm}
    \caption{my capt}
    \begin{minipage}{\dimexpr\textwidth-2\algomargin\relax}
    \begin{enumerate}
        \item step 1
        \item step 2
        \item step 3 
        \begin{equation}\label{alg1}
            \tau = x + y.
        \end{equation}
        \item step 5
    \end{enumerate}
    \end{minipage}
\end{algorithm}
I have an equation:
\begin{equation}\label{myeq}
        \alpha = x^2 y.
    \end{equation}
\end{document}

Here in the above MWE, I use a minipage environment to avoid getting an overfull hbox error. I want to align the equation numbers vertically inside and outside the algorithm. It looks like in the figure below. I want to align equations (1) and (2):

How can I do that?

This question is very similar to the one posted here: https://tex.stackexchange.com/a/460466/139314 Instead of a box, I have an algorithm environment.

Many thanks in advance.

Answer 1

This aligns the inner equation to the outer equation (as opposed to aligning the outer to the inner). It uses \makebox to overlap the left margin, and negative \hspace to overlap the right margin.

\documentclass[12pt, a4paper]{report}
\usepackage{mathtools}
\usepackage[ruled]{algorithm2e}
\begin{document}
\begin{algorithm}
    \caption{my capt}
    \begin{enumerate}
        \item step 1
        \item step 2
        \item step 3\
        \makebox[\dimexpr \linewidth-2\algomargin][r]{% overlap left margin
        \begin{minipage}{\textwidth}% equation is in vmode
        \begin{equation}\label{alg1}
            \tau = x + y.
        \end{equation}
        \end{minipage}\hspace{-\algomargin}}% overlap right margin
        \item step 5
    \end{enumerate}
\end{algorithm}
I have an equation:
\begin{equation}\label{myeq}
        \alpha = x^2 y.
    \end{equation}
\end{document}