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\subsection{RW Basic binary I/O utilities}
\label{sec:pkg:rw}
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The {\tt rw} package provides a very rudimentary binary I/O capability
for quickly writing {\it single record} direct-access Fortran binary files. 
It is primarily used for writing diagnostic output.

\subsubsection{Introduction}
Package {\tt rw} is an interface to the more general {\tt mdsio} package.
The {\tt rw} package can be used to write or read direct-access Fortran 
binary files for two-dimensional XY and three-dimensional XYZ arrays. 
The arrays are assumed to have been declared according to the standard
MITgcm two-dimensional or three-dimensional floating point array type:
\begin{verbatim}
C     Example of declaring a standard two dimensional "long" 
C     floating point type array (the _RL macro is usually 
C     mapped to 64-bit floats in most configurations)
      _RL anArray(1-OLx:sNx+OLx,1-OLy:sNy+OLy,nSx,nSy)
\end{verbatim}

Each call to an {\tt rw} read or write routine will read (or write) to
the first record of a file. To write direct access Fortran files with
multiple records use the package {\tt mdsio} (see section
\ref{sec:pkg:mdsio}).  To write self-describing files that contain
embedded information describing the variables being written and the
spatial and temporal locations of those variables use the package {\tt
  mnc} (see section \ref{sec:pkg:mnc}) which produces
\htlink{netCDF}{http://www.unidata.ucar.edu/packages/netcdf}
\cite{rew:97} based output.

%% \subsubsection{Key subroutines, parameters and files}
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%% The {\tt rw} package has