\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{algorithm}
\usepackage{algorithmic}
\usepackage{relsize}

\makeatletter

\def\textsubscript#1{\ensuremath{_{\mbox{\textscale{.6}{#1}}}}}
\makeatother



\begin{document}

\begin{algorithm}[H]

\caption{OneR}\label{euclid}

\textbf{Input:} D = {x1, x2, · · · , xn} // Training data

\textbf{Output: }OneR Model

\textbf{Method:}


\begin{algorithmic}[1]

 \FOR {$ \textit{each attribute}, A\textsubscript{i}  \epsilon  D, $}
  \FOR {$ \textit{each attribute value}, A\textsubscript{ij}  \epsilon    A\textsubscript{i},  $}

    \STATE $ \textbf{Make a classification rule:}$

    \STATE $ \textit{ count how often each class appears} $

    \STATE $ \textit{ find the most frequent class }$

    \STATE $ \textit{ make the rule assign that class to this  A\textsubscript{ij}} $

\ENDFOR

   \STATE $ \textit{ Calculate the error rate of this attribute’s  A\textsubscript{ij} rule.} $

\ENDFOR

   \STATE $ \textit{ Choose the attribute  A\textsubscript{i}} \epsilon D \textit{with the smallest error rate.} $

\end{algorithmic}
\end{algorithm}
\end{document}