5

Broken box is showing in the compiled pdf. See my LaTeX code below:

\documentclass{article}
\usepackage{graphicx}
\usepackage{a4wide}

\usepackage{tabularx} 

\makeatletter
\newenvironment{problem}[2][]{%
  \def\problem@arg{#1}%
  \def\problem@framed{framed}%
  \def\problem@lined{lined}%
  \def\problem@doublelined{doublelined}%
  \ifx\problem@arg\@empty%
    \def\problem@hline{}%
  \else%
    \ifx\problem@arg\problem@doublelined%
      \def\problem@hline{\hline\hline}%
    \else%
      \def\problem@hline{\hline}%
    \fi%
  \fi%
  \ifx\problem@arg\problem@framed%
    \def\problem@table{\tabularx{\textwidth}{|>{\bfseries}lX|c}}%
    \def\problem@title{\multicolumn{2}{|l|}{%
        \raisebox{-\fboxsep}{\textsc{\Large #2}}%
      }}%
  \else
    \def\problem@table{\tabularx{\textwidth}{>{\bfseries}lXc}}%
    \def\problem@title{\multicolumn{2}{l}{%
        \raisebox{-\fboxsep}{\textsc{\Large #2}}%
      }}%
  \fi%
  \bigskip\par\noindent%
  \renewcommand{\arraystretch}{1.2}%
    \problem@table%
      \problem@hline%
      \problem@title\\[2\fboxsep]%
}{%
      \\\problem@hline%
    \endtabularx%
  \medskip\par%
}
\makeatother


\section{Introduction}

Given  two graphs $G =(V,E_1)$ and $H = (V,E_2)$  are said to be isomorphic if there exists a bijection $\phi: V \mapsto V$ that preserves the edges and non-edges. Similarliy two groups $(G,\circ)$ and $(H,\times )$ are said to be isomorphic if there exist an bijective map from $\pi : G \mapsto H$ such that $\forall a,b \in G, \pi(a\circ b) = \pi(a) \times \pi(b)$.
Graph isomorphism is strongly related to group theoretic problems like group isomorphism, group intersection etc. Grpah Isomorphism is known to be in $\mathsf{NP}$, not known to be in $\mathsf{P}$ and very unlikely to be $\mathsf{NP}$-complete.

\begin{problem}[framed]{Graph Isomorphism (GI)}
  Inpu: & Two graphs $G=(V,E_1)$ and $H=(V,E_2)$. \\
  Problem: & Is $G$ isomorphic to $H$? \\

\end{problem}
\end{document}

enter image description here

  • Try leaving out the \\ of the last line. – CarLaTeX Feb 5 '18 at 6:46
  • Off-topic but still of interest: (i) Use \colon instead of : (two instances) in the paragraph that precedes the problem environment. Why? In math mode, : is taken to be a relational operator, which doesn't apply here. (ii) The readability of all-uppercase and all-smallcaps text strings improves significantly if these strings are letterspaced. To achieve this goal, I suggest you load the microtype package and encase both instances of \textsc{\Large #2} in \textls{...} directives. (iii) Writing $\mathsf{NP}$ seems unnecessarily complicated; try writing \textsf{NP} instead. – Mico Feb 5 '18 at 8:06
7

Please do not use package a4wide any longer! See Ctan!

To get rid of the broken box you have to delete/comment the \\ I marked with <===== in the following MWE:

\documentclass{article}

%\usepackage{a4wide} % <=========================== use package geometry
\usepackage[a4paper]{geometry}
\usepackage{graphicx}
\usepackage{tabularx}

\makeatletter
\newenvironment{problem}[2][]{%
  \def\problem@arg{#1}%
  \def\problem@framed{framed}%
  \def\problem@lined{lined}%
  \def\problem@doublelined{doublelined}%
  \ifx\problem@arg\@empty%
    \def\problem@hline{}%
  \else%
    \ifx\problem@arg\problem@doublelined%
      \def\problem@hline{\hline\hline}%
    \else%
      \def\problem@hline{\hline}%
    \fi%
  \fi%
  \ifx\problem@arg\problem@framed%
    \def\problem@table{\tabularx{\textwidth}{|>{\bfseries}lX|c}}%
    \def\problem@title{\multicolumn{2}{|l|}{%
        \raisebox{-\fboxsep}{\textsc{\Large #2}}%
      }}%
  \else
    \def\problem@table{\tabularx{\textwidth}{>{\bfseries}lXc}}%
    \def\problem@title{\multicolumn{2}{l}{%
        \raisebox{-\fboxsep}{\textsc{\Large #2}}%
      }}%
  \fi%
  \bigskip\par\noindent%
  \renewcommand{\arraystretch}{1.2}%
    \problem@table%
      \problem@hline%
      \problem@title\\[2\fboxsep]%
}{%
%     \\% <=============================================================
      \problem@hline%
    \endtabularx%
  \medskip\par%
}
\makeatother


\begin{document}

\section{Introduction}

Given  two graphs $G =(V,E_1)$ and $H = (V,E_2)$  are said to be 
isomorphic if there exists a bijection $\phi: V \mapsto V$ that 
preserves the edges and non-edges. Similarliy two groups $(G,\circ)$ and 
$(H,\times )$ are said to be isomorphic if there exist an bijective map 
from $\pi : G \mapsto H$ such that 
$\forall a,b \in G, \pi(a\circ b) = \pi(a) \times \pi(b)$.
Graph isomorphism is strongly related to group theoretic problems like 
group isomorphism, group intersection etc. Grpah Isomorphism is known 
to be in $\mathsf{NP}$, not known to be in $\mathsf{P}$ and very 
unlikely to be $\mathsf{NP}$-complete.

\begin{problem}[framed]{Graph Isomorphism (GI)}
  Input: & Two graphs $G=(V,E_1)$ and $H=(V,E_2)$. \\
  Problem: & Is $G$ isomorphic to $H$? \\

\end{problem}
\end{document}

You get the result:

enter image description here

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