algorithm2e vertical line indentation

Question

I really like the vertical line feature of algorithm2e, but I ran into trouble with it when I try to indent an if statement. I used the following code.

\documentclass{article}
\usepackage{amssymb,amsthm,fullpage,amsmath}
\usepackage[ruled,vlined,boxed]{algorithm2e}

\begin{document}

\begin{algorithm}[H]
 \caption{\bf Generic Line Search Algorithm}

 {\bf Inputs:} Starting point $x_0$, initial step size parameter $\alpha_0$. \\
 \For{$k = 0,1,2,\dots$}{
    \nl {\bf Gradient approximation $g(x_k)$:}\\ \Indp
    Compute an approximation $g(x_k)$ of $\nabla \phi(x_k)$. \\ \Indm
    \nl {\bf Construct a search direction $d_k$:}\\ \Indp
    Construct a search direction $d_k$, e.g., $d_k = - g(x_k)$.\\ \Indm
    \nl {\bf Compute step size $\alpha_k$ and update the iterate:} \\ \Indp
    \eIf{sufficient decrease condition is satisfied}{
        $x_{k+1} = x_k - \alpha_k d_k$ and $\alpha_{k+1} \gets \tau^{-1} \alpha_k$
    }{
        $x_{k+1} = x_k$ and $\alpha_{k+1} \gets \tau \alpha_k$
    } 
 }
\end{algorithm}

\end{document}

The texts were indented but the vertical lines in the if statement were not, as shown in the picture. Does anyone know how to indent the vertical lines?

Answer 1

Try this:

• \skiptext (before vline space) and \skiprule (after vline space) are additionally updated inside indent adjusting command.
• No change to algorithm input.

\documentclass{article}
%\usepackage{amssymb,amsthm,fullpage,amsmath}
\usepackage[ruled,vlined,boxed]{algorithm2e}

\makeatletter
\renewcommand{\Indentp}[1]{%
  \advance\leftskip by #1
  \advance\skiptext by -#1
  \advance\skiprule by #1}%
\renewcommand{\Indp}{\algocf@adjustskipindent\Indentp{\algoskipindent}}
\renewcommand{\Indpp}{\Indentp{0.5em}}%
\renewcommand{\Indm}{\algocf@adjustskipindent\Indentp{-\algoskipindent}}
\renewcommand{\Indmm}{\Indentp{-0.5em}}%
\makeatother

\begin{document}
\begin{algorithm}[H]
 \caption{\bfseries OP's example}

 \textbf{Inputs:} Starting point $x_0$, initial step size parameter $\alpha_0$. \\
 \For{$k = 0,1,2,\dots$}{
    \nl \textbf{Gradient approximation $g(x_k)$:}\\ \Indp
    Compute an approximation $g(x_k)$ of $\nabla \phi(x_k)$. \\ \Indm
    \nl \textbf{Construct a search direction $d_k$:}\\ \Indp
    Construct a search direction $d_k$, e.g., $d_k = - g(x_k)$.\\ \Indm
    \nl \textbf{Compute step size $\alpha_k$ and update the iterate:} \\ \Indp
    \eIf{sufficient decrease condition is satisfied}{
        $x_{k+1} = x_k - \alpha_k d_k$ and $\alpha_{k+1} \gets \tau^{-1} \alpha_k$
    }{
        $x_{k+1} = x_k$ and $\alpha_{k+1} \gets \tau \alpha_k$
    }
 }
\end{algorithm}


\begin{algorithm}
  \caption{More tests}
  \nl test \\
  \eIf{sufficient decrease condition is satisfied}{
    if clause
  }{
    else clause
  }
  \nl test \\ \Indp\Indp
  \eIf{sufficient decrease condition is satisfied}{
    if clause
  }{
    else clause
  } \Indm
  \nl test \\
  \eIf{sufficient decrease condition is satisfied}{
    if clause
  }{
    else clause
  }
\end{algorithm}
\end{document}

Notes:

• \Indp (or \Indm) increases (or reduces) indentation by \algoskipindent (aka "step").
• This might not be the perfect solution, since I have not fully understand the algorithm2e internals \algocf@Vline and \algocf@Vsline.

Answer 2

As said in the comments using vertical lines with \indp and \indm is a little buggy. The alternative is to turn the Compute step size into a block and thus allow the algorithm2e package to handle the indentation on its own in a better way.

This is done using \SetKwBlock{Begin}{begin}{end} macro:

\SetKwBlock{NewBlock}{Compute step size $\alpha_k$ and update the iterate:}{}

This would indent the if nicely, however, it would also add a vertical line for the new Compute step size block. To remove that vertical line we add \SetAlgoNoLine and \SetAlgoVlined.

MWE:

\documentclass{article}
\usepackage{amssymb,amsthm,fullpage,amsmath}
\usepackage[ruled,vlined,boxed]{algorithm2e}


\begin{document}

\begin{algorithm}[H]
\DontPrintSemicolon
\SetKwBlock{NewBlock}{Compute step size $\alpha_k$ and update the iterate:}{}
\caption{\bf Generic Line Search Algorithm}

\KwIn{Starting point $x_0$, initial step size parameter $\alpha_0$.}\;
\For{$k = 0,1,2,\dots$}{
   \nl {\bf Gradient approximation $g(x_k)$:}\; 
   \Indp Compute an approximation $g(x_k)$ of $\nabla \phi(x_k)$.\;

   \Indm \nl {\bf Construct a search direction $d_k$:}\; 
   \Indp Construct a search direction $d_k$, e.g., $d_k = - g(x_k)$.\; 


   \Indm\nl\SetAlgoNoLine\NewBlock{ \SetAlgoVlined\eIf{sufficient decrease condition is satisfied}{
        $x_{k+1} = x_k - \alpha_k d_k$ and $\alpha_{k+1} \gets \tau^{-1} \alpha_k$\;
        }{
        $x_{k+1} = x_k$ and $\alpha_{k+1} \gets \tau \alpha_k$\;
        }
    }
 }
\end{algorithm}

\end{document}

And the outcome:

Notice the following improvements from OP's MWE:

1. At the end of each line \; is used (no need for \\). In order not to print semicolons we use DontPrintSemicolon.
2. We use algorithm2e built-in \KwIn macro.