\par
\section{Data Structure}
\label{section:Perm:dataStructure}
\par
The {\tt Perm} object can contain two permutation vectors,
an {\it old-to-new} and a {\it new-to-old} permutation.
One or both may be present in the structure.
\par
The {\tt Perm} structure has four fields.
\begin{itemize}
\item {\tt int isPresent} : flag to tell which vectors are present 
\begin{itemize}
\item 0 $\longrightarrow$ neither is present 
\item 1 $\longrightarrow$ {\tt newToOld} is present, {\tt oldToNew} is not
\item 2 $\longrightarrow$ {\tt oldToNew} is present, {\tt newToOld} is not
\item 3 $\longrightarrow$ both {\tt newToOld} and {\tt oldToNew} are present 
\end{itemize}
\item {\tt int size} : dimension of the vectors 
\item {\tt int *newToOld} : pointer to the new-to-old vector 
\item {\tt int *oldToNew} : pointer to the old-to-new vector 
\end{itemize}