\subsection{Description}

The ordering step will reorder the unknowns of the matrix to minimize
fill-in during factorisation.\\
This step is description in \hyperref[ordering]{\ref{ordering}}

\subsection{Parameters}

To call ordering step, \iparm{IPARM\_START\_TASK} has to be
set to \texttt{API\_TASK\_ORDERING} or previous task and
\iparm{IPARM\_END\_TASK} must be greater or equal to ordering
one.


Ordering can be computed with \textsc{Scotch} or \texttt{Metis}.\\
To enable \texttt{Metis}, user has to uncomment the corresponding part of the 
\texttt{config.in} file.
\index{config.in}
\index{scotch@\textsc{Scotch}}
\index{metis@\textsc{Metis}}
To select the ordering software, user may set \iparm{IPARM\_ORDERING}
to :
\begin{itemize}
\item \texttt{API\_ORDER\_SCOTCH} : use \texttt{Scotch} for the ordering (default) 
\item \texttt{API\_ORDER\_METIS}  : use \texttt{Metis} for the ordering.
\end{itemize}

To have a finer control on the ordering software, user can set \iparm{IPARM\_DEFAULT\_ORDERING} to \texttt{API\_YES} and modify those parameters: 
\begin{itemize}
\item when using \texttt{Scotch}~:
  \begin{description}
  \item[\iparm{IPARM\_ORDERING\_SWITCH\_LEVEL}~:] ordering switch
    level (see Scotch User's Guide),
  \item[\iparm{IPARM\_ORDERING\_CMIN}~:] ordering cmin parameter
    (see Scotch User's Guide),
  \item[\iparm{IPARM\_ORDERING\_CMAX}~:] ordering cmax parameter
    (see Scotch User's Guide),
  \item[\iparm{IPARM\_ORDERING\_FRAT}~:] ordering frat parameter
    ($\times 100$) (see Scotch User's Guide).
    \index{scotch@\textsc{Scotch}}
  \end{description}
\item when using \texttt{Metis}~:
  \begin{description}
  \item[\iparm{IPARM\_ORDERING\_SWITCH\_LEVEL}~:] Metis ctype option,
  \item[\iparm{IPARM\_ORDERING\_CMIN}~:] Metis itype option,
  \item[\iparm{IPARM\_ORDERING\_CMAX}~:] Metis rtype option,
  \item[\iparm{IPARM\_ORDERING\_FRAT}~:] Metis dbglvl option,
  \item[\iparm{IPARM\_STATIC\_PIVOTING}~:] Metis oflags option,
  \item[\iparm{IPARM\_METIS\_PFACTOR}~:] Metis pfactor option,
  \item[\iparm{IPARM\_NNZERO}~:] Metis nseps option.
  \end{description}
  \index{metis@\texttt{Metis}}
\end{itemize}
