Indenting lines of code in algorithm

Question

I am writting algorithm which has two stages. How can I indent code for stage one and for stage two?

\begin{algorithm}[H]
\caption*{my algorithm}
\begin{algorithmic}
    \STATE \textbf{Stage one:} this is stage one
    \FORALL{i}
        \STATE do something
    \ENDFOR
    \STATE \textbf{Stage two:} this is stage two
    \STATE Update the trie: 
    \FORALL{j}
    \STATE do something
    \ENDFOR
\end{algorithmic}
\end{algorithm}

Answer 1

In the following example code I defined two new commands allowing you to change the indentation; simply enclose the desired fragment using \bindent, \eindent; the length \myindent controls the indent amount:

\documentclass{article}
\usepackage{algorithm,algorithmic}
\usepackage{caption}

\newlength\myindent
\setlength\myindent{2em}
\newcommand\bindent{%
  \begingroup
  \setlength{\itemindent}{\myindent}
  \addtolength{\algorithmicindent}{\myindent}
}
\newcommand\eindent{\endgroup}

\begin{document}

\begin{algorithm}[H]
\caption*{my algorithm}
\begin{algorithmic}
    \STATE \textbf{Stage one:} this is stage one
    \bindent
    \FORALL{i}
        \STATE do something
    \ENDFOR
    \eindent
    \STATE \textbf{Stage two:} this is stage two
    \bindent
    \STATE Update the trie: 
    \FORALL{j}
    \STATE do something
    \ENDFOR
    \eindent
\end{algorithmic}
\end{algorithm}

\end{document}

Some comments to the code:

\newlength\myindent % define a new length \myindent
\setlength\myindent{6em} % assign the length 2em to \myindet
\newcommand\bindent{%
  \begingroup % starts a group (to keep changes local)
  \setlength{\itemindent}{\myindent} % set itemindent (algorithmic internally uses a list) to the value of \mylength
  \addtolength{\algorithmicindent}{\myindent} % adds \mylength to the default indentation used by algorithmic
}
\newcommand\eindent{\endgroup} % closes a group