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% $Header: /u/gcmpack/manual/part6/mnc.tex,v 1.10 2004/07/05 16:35:32 edhill Exp $ |
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% $Name: $ |
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\section{NetCDF I/O Integration: MNC} |
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\label{sec:pkg:mnc} |
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The \texttt{mnc} package is a set of convenience routines written to |
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expedite the process of creating, appending, and reading NetCDF files. |
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NetCDF is an increasingly popular self-describing file format |
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\cite{rew:97} intended primarily for scientific data sets. An |
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extensive collection of NetCDF reference papers, user guides, |
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software, FAQs, and other information can be obtained from UCAR's web |
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site at: |
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\begin{rawhtml} <A href="http://www.unidata.ucar.edu/packages/netcdf/"> \end{rawhtml} |
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\begin{verbatim} |
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http://www.unidata.ucar.edu/packages/netcdf/ |
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\end{verbatim} |
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\begin{rawhtml} </A> \end{rawhtml} |
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\subsection{Introduction} |
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The \texttt{mnc} package is a two-level convenience library (or |
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``wrapper'') for most of the NetCDF Fortran API. Its purpose is to |
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streamline the user interface to NetCDF by maintaining internal |
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relations (look-up tables) keyed with strings (or names) and entities |
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such as NetCDF files, variables, and attributes. |
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The two levels of the \texttt{mnc} package are: |
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\begin{description} |
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|
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\item[Upper level] \ |
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The upper level contains information about two kinds of |
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associations: |
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\begin{description} |
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\item[grid type] is lookup table indexed with a grid type name. |
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Each grid type name is associated with a number of dimensions, the |
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dimension sizes (one of which may be unlimited), and starting and |
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ending index arrays. The intent is to store all the necessary |
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size and shape information for the Fortran arrays containing |
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MITgcm--style ``tile'' variables (that is, a central region |
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surrounded by a variably-sized ``halo'' or exchange region as |
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shown in Figures \ref{fig:communication_primitives} and |
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\ref{fig:tiling-strategy}). |
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|
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\item[variable type] is a lookup table indexed by a variable type |
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name. For each name, the table contains a reference to a grid |
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type for the variable and the names and values of various |
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attributes. |
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\end{description} |
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Within the upper level, these associations are not permanently tied |
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to any particular NetCDF file. This allows the information to be |
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re-used over multiple file reads and writes. |
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\item[Lower level] \ |
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In the lower (or internal) level, associations are stored for NetCDF |
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files and many of the entities that they contain including |
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dimensions, variables, and global attributes. All associations are |
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on a per-file basis. Thus, each entity is tied to a unique NetCDF |
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file and will be created or destroyed when files are, respectively, |
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opened or closed. |
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|
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\end{description} |
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\subsection{Using MNC} |
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\subsubsection{Grid--Types and Variable--Types} |
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As a convenience for users, the MNC package includes numerous routines |
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to aid in the writing of data to NetCDF format. Probably the biggest |
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convenience is the use of pre-defined ``grid types'' and ``variable |
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types''. These ``types'' are simply look-up tables that store |
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dimensions, indicies, attributes, and other information that can all |
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be retrieved using a single character string. |
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The ``grid types'' are a way of mapping variables within MITgcm to |
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NetCDF arrays. Within MITgcm, most spatial variables are defined |
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using two-- or three--dimensional arrays with ``overlap'' regions (see |
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Figures \ref{fig:communication_primitives}, a possible vertical index, |
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and \ref{fig:tiling-strategy}) and tile indicies such as the following |
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``U'' velocity: |
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\begin{verbatim} |
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_RL uVel (1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy) |
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\end{verbatim} |
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as defined in \filelink{model/inc/DYNVARS.h}{model-inc-DYNVARS.h} |
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The grid type is a character string that encodes the presence and |
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types associated with the four possible dimensions. The character |
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string follows the format |
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\begin{center} |
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\texttt{H0\_H1\_H2\_\_V\_\_T} |
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\end{center} |
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where the terms \textit{H0}, \textit{H1}, \textit{H2}, \textit{V}, |
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\textit{T} can be almost any combination of the following: |
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\begin{center} |
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\begin{tabular}[h]{|ccc|c|c|}\hline |
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\multicolumn{3}{|c|}{Horizontal} & Vertical & Time \\ |
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\textbf{H0}: location & \textbf{H1}: dimensions & \textbf{H2}: halo |
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& \textbf{V}: location & \textbf{T}: level \\\hline |
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\texttt{-} & xy & Hn & \texttt{-} & \texttt{-} \\ |
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U & x & Hy & i & t \\ |
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V & y & & c & \\ |
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Cen & & & & \\ |
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Cor & & & & \\\hline |
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\end{tabular} |
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\end{center} |
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A example list of all pre-defined combinations is contained in the |
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file |
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\begin{center} |
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\texttt{pkg/mnc/pre-defined\_grids.txt}. |
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\end{center} |
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|
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The variable type is an association between a variable type name and the |
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following items: |
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\begin{center} |
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\begin{tabular}[h]{|l|l|}\hline |
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\textbf{Item} & \textbf{Purpose} \\\hline |
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grid type & defines the in-memory arrangement \\ |
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\texttt{bi,bj} dimensions & tiling indices, if present \\\hline |
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\end{tabular} |
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\end{center} |
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and is used by the \texttt{mnc\_cw\_*\_[R|W]} subroutines for reading |
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and writing variables. |
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\subsubsection{An Example} |
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Writing variables to NetCDF files can be accomplished in as few as two |
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function calls. The first function call defines a variable type, |
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associates it with a name (character string), and provides additional |
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information about the indicies for the tile (\texttt{bi},\texttt{bj}) |
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dimensions. The second function call will write the data at, if |
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necessary, the current time level within the model. |
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Examples of the initialization calls can be found in the file |
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\filelink{model/src/ini\_mnc\_io.F}{model-src-ini_mnc_io.F} |
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where these function calls: |
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{\footnotesize |
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\begin{verbatim} |
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C Create MNC definitions for DYNVARS.h variables |
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CALL MNC_CW_ADD_VNAME('iter', '-_-_--__-__t', 0,0, myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('iter',1, |
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& 'long_name','iteration_count', myThid) |
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CALL MNC_CW_ADD_VNAME('model_time', '-_-_--__-__t', 0,0, myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('model_time',1, |
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& 'long_name','Model Time', myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('model_time',1,'units','s', myThid) |
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|
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CALL MNC_CW_ADD_VNAME('U', 'U_xy_Hn__C__t', 4,5, myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('U',1,'units','m/s', myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('U',1, |
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& 'coordinates','XU YU RC iter', myThid) |
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CALL MNC_CW_ADD_VNAME('T', 'Cen_xy_Hn__C__t', 4,5, myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('T',1,'units','degC', myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('T',1,'long_name', |
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& 'potential_temperature', myThid) |
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CALL MNC_CW_ADD_VATTR_TEXT('T',1, |
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& 'coordinates','XC YC RC iter', myThid) |
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\end{verbatim} |
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} |
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{\noindent initialize four \texttt{VNAME}s and add one or more NetCDF |
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attributes to each.} |
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The four variables defined above are subsequently written at specific |
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time steps within |
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\filelink{model/src/write\_state.F}{model-src-write_state.F} |
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using the function calls: |
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{\footnotesize |
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\begin{verbatim} |
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C Write dynvars using the MNC package |
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CALL MNC_CW_SET_UDIM('state', -1, myThid) |
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CALL MNC_CW_I_W('I','state',0,0,'iter', myIter, myThid) |
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CALL MNC_CW_SET_UDIM('state', 0, myThid) |
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CALL MNC_CW_RL_W('D','state',0,0,'model_time',myTime, myThid) |
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CALL MNC_CW_RL_W('D','state',0,0,'U', uVel, myThid) |
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CALL MNC_CW_RL_W('D','state',0,0,'T', theta, myThid) |
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\end{verbatim} |
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} |
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\subsubsection{Parameters} |
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Most of the MNC--related parameters are contained within a Fortran |
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namelist file called \texttt{data.mnc}. If this file does not exist, |
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then the MNC package will interpret that as an indication that it is |
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not to be used. If the \texttt{data.mnc} file does exist, then it may |
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contain the following parameters: |
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\begin{center} |
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{\footnotesize |
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\begin{tabular}[htb]{|l|c|l|l|}\hline |
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\textbf{Name} & \textbf{T} & |
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\textbf{Default} & \textbf{Description} \\\hline |
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& & & \\ |
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\texttt{useMNC} & L & \texttt{.FALSE.} & |
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\textbf{overall MNC ON/OFF switch} \\ |
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\texttt{mnc\_echo\_gvtypes} & L & \texttt{.FALSE.} & |
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echo pre-defined ``types'' (debugging) \\ |
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\texttt{mnc\_use\_outdir} & L & \texttt{.FALSE.} & |
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create a directory for output \\ |
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\texttt{mnc\_outdir\_str} & S & \texttt{'mnc\_'} & |
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output directory name \\ |
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\texttt{mnc\_outdir\_date} & L & \texttt{.FALSE.} & |
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embed date in the output dir name \\ |
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\texttt{pickup\_write\_mnc} & L & \texttt{.FALSE.} & |
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use MNC to write (create) pickup files \\ |
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\texttt{pickup\_read\_mnc} & L & \texttt{.FALSE.} & |
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use MNC to read pickup files \\ |
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\texttt{mnc\_use\_indir} & L & \texttt{.FALSE.} & |
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use a directory (path) for input \\ |
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\texttt{mnc\_indir\_str} & S & \texttt{''} & |
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input directory (or path) name \\ |
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\texttt{snapshot\_mnc} & L & \texttt{.FALSE.} & |
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write \texttt{snapshot} (instantaneous) w/MNC \\ |
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\texttt{monitor\_mnc} & L & \texttt{.FALSE.} & |
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write \texttt{monitor} w/MNC \\ |
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\texttt{timeave\_mnc} & L & \texttt{.FALSE.} & |
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write \texttt{timeave} w/MNC \\\hline |
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\end{tabular} |
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} |
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\end{center} |
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|
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Additional MNC--related parameters are contained within the main |
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\texttt{data} namelist file and in some of the namelist files for |
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individual packages. These options are: |
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\begin{center} |
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{\footnotesize |
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\begin{tabular}[htb]{|l|c|l|l|}\hline |
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\textbf{Name} & \textbf{T} & |
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\textbf{Default} & \textbf{Description} \\\hline |
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\multicolumn{4}{|c|}{\ } \\ |
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\multicolumn{4}{|c|}{Main namelist file: |
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``\textbf{data}''} \\\hline |
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\texttt{snapshot\_ioinc} & L & \texttt{.FALSE.} & |
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write \texttt{snapshot} ``inclusively'' \\ |
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\texttt{timeave\_ioinc} & L & \texttt{.FALSE.} & |
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write \texttt{timeave} ``inclusively'' \\ |
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\texttt{monitor\_ioinc} & L & \texttt{.FALSE.} & |
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write \texttt{monitor} ``inclusively'' \\\hline |
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\multicolumn{4}{|c|}{\ } \\ |
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\multicolumn{4}{|c|}{Diagnostics namelist file: |
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``\textbf{data.diagnostics}''} \\\hline |
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\texttt{diag\_mnc} & L & \texttt{.FALSE.} & |
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write \texttt{diagnostics} w/MNC \\ |
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\texttt{diag\_ioinc} & L & \texttt{.FALSE.} & |
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write \texttt{diagnostics} ``inclusively'' \\\hline |
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\end{tabular} |
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} |
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\end{center} |
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By default, turning on MNC for a particular output stream will result |
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in turning off all the corresponding (usually, default) MDSIO or |
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STDOUT output mechanisms. In other words, output defaults to being an |
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exclusive selection. To enable multiple kinds of simultaneous output, |
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flags of the form \texttt{NAME\_ioinc} can be used where \texttt{NAME} |
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corresponds to the various MNC output flags. When a |
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\texttt{NAME\_ioinc} flag is set to \texttt{.TRUE.}, then multiple |
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forms of output are allowed for the \texttt{NAME} output mechanism. |
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The intent of this design is that typical users will only want one |
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kind of output while people debugging the code (particularly the I/O |
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routines) may want simultaneous types of output. |
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This ``inclusive'' versus ``exclusive'' design is easily applied in |
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cases where three or more kinds of output may be generated. Thus, it |
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can be readily extended to additional new output types (eg. HDF5). |
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Input types are always exclusive. |
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