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revision 1.2 by cnh, Wed Jan 28 21:27:45 2004 UTC revision 1.14 by edhill, Sat Dec 11 22:03:32 2004 UTC
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1  % $Header$  % $Header$
2  % $Name$  % $Name$
3    
4  %%  * Introduction  \section{NetCDF I/O Integration: MNC}
 %%    o what it does, citations (refs go into mitgcm_manual.bib,  
 %%      preferably in alphabetic order)  
 %%    o Equations  
 %%  * Key subroutines and parameters  
 %%  * Reference material (auto generated from Protex and structured comments)  
 %%    o automatically inserted at \section{Reference}  
   
   
 \section{MNC: the MITgcm NetCDF Package}  
5  \label{sec:pkg:mnc}  \label{sec:pkg:mnc}
6    \begin{rawhtml}
7    <!-- CMIREDIR:package_mnc: -->
8    \end{rawhtml}
9    
10    The \texttt{mnc} package is a set of convenience routines written to
11    expedite the process of creating, appending, and reading NetCDF files.
12    NetCDF is an increasingly popular self-describing file format
13    \cite{rew:97} intended primarily for scientific data sets.  An
14    extensive collection of NetCDF reference papers, user guides,
15    software, FAQs, and other information can be obtained from UCAR's web
16    site at:
17    \begin{rawhtml} <A href="http://www.unidata.ucar.edu/packages/netcdf/"> \end{rawhtml}
18    \begin{verbatim}
19    http://www.unidata.ucar.edu/packages/netcdf/
20    \end{verbatim}
21    \begin{rawhtml} </A> \end{rawhtml}
22    
23    
24    \subsection{Using MNC}
25    
26    \subsubsection{MNC Configuration}
27    
28    As with all MITgcm packages, MNC can be turned on or off at compile time
29    using the \texttt{packages.conf} file or the \texttt{genmake2}
30    \texttt{-enable=mnc} or \texttt{-disable=mnc} switches.
31    
32    While MNC is likely to work ``as is'', there are a few compile--time
33    constants that may need to be increased for simulations that employ
34    large numbers of tiles within each process.  Note that the important
35    quantity is the maximum number of tiles \textbf{per process}.  Since
36    MPI configurations tend to distribute large numbers of tiles over
37    relatively large numbers of MPI processes, these constants will rarely
38    need to be increased.
39    
40    If MNC runs out of space within its ``lookup'' tables during a
41    simulation, then it will provide an error message along with a
42    recommendation of which parameter to increase.  The parameters are all
43    located within \filelink{pkg/mnc/mnc\_common.h}{pkg-mnc-mnc_common.h}
44    and the ones that may need to be increased are:
45    
46    \begin{center}
47      {\footnotesize
48        \begin{tabular}[htb]{|l|r|l|}\hline
49          \textbf{Name}  &  
50          \textbf{Default}  &  \textbf{Description}  \\\hline
51          &  &  \\
52          \texttt{MNC\_MAX\_ID}  &  1000  &
53          \textbf{IDs for various low-level entities}  \\
54          \texttt{MNC\_MAX\_INFO}  &   400  &
55          \textbf{IDs (mostly for object sizes)}  \\
56          \texttt{MNC\_CW\_MAX\_I}  &  150  &
57          \textbf{IDs for the ``wrapper'' layer}  \\\hline
58        \end{tabular}
59      }
60    \end{center}
61    
62    In those rare cases where MNC ``out-of-memory'' error messages are
63    encountered, it is a good idea to increase the too-small parameter by
64    a factor of \textbf{2--10} in order to avoid wasting time on an
65    iterative compile--test sequence.
66    
67    
68    \subsubsection{MNC Inputs}
69    
70    For run-time configuration, most of the MNC--related model parameters
71    are contained within a Fortran namelist file called \texttt{data.mnc}.
72    If this file does not exist, then the MNC package will interpret that
73    as an indication that it is not to be used.  If the \texttt{data.mnc}
74    file does exist, then it may contain the following parameters:
75    
76    \begin{center}
77      {\footnotesize
78        \begin{tabular}[htb]{|l|c|l|l|}\hline
79          \textbf{Name}  &  \textbf{T}  &  
80          \textbf{Default}  &  \textbf{Description}  \\\hline
81          &  &  &  \\
82          \texttt{useMNC}  &  L  & \texttt{.FALSE.}  &  
83          \textbf{overall MNC ON/OFF switch}  \\
84          \texttt{mnc\_echo\_gvtypes}  &  L  & \texttt{.FALSE.}  &  
85          echo pre-defined ``types'' (debugging)   \\
86          \texttt{mnc\_use\_outdir}  &  L  & \texttt{.FALSE.}  &  
87          create a directory for output  \\
88          \texttt{mnc\_outdir\_str}  &  S  & \texttt{'mnc\_'}  &  
89          output directory name \\
90          \texttt{mnc\_outdir\_date}  &  L  & \texttt{.FALSE.}  &  
91          embed date in the output dir name  \\
92          \texttt{pickup\_write\_mnc}  &  L  & \texttt{.FALSE.}  &  
93          use MNC to write (create) pickup files  \\
94          \texttt{pickup\_read\_mnc}  &  L  & \texttt{.FALSE.}  &  
95          use MNC to read pickup files  \\
96          \texttt{mnc\_use\_indir}  &  L  & \texttt{.FALSE.}  &  
97          use a directory (path) for input  \\
98          \texttt{mnc\_indir\_str}  &  S  & \texttt{''}  &  
99          input directory (or path) name  \\
100          \texttt{snapshot\_mnc}  &  L  & \texttt{.FALSE.}  &  
101          write \texttt{snapshot} (instantaneous) w/MNC  \\
102          \texttt{monitor\_mnc}  &  L  & \texttt{.FALSE.}  &  
103          write \texttt{monitor} w/MNC  \\
104          \texttt{timeave\_mnc}  &  L  & \texttt{.FALSE.}  &  
105          write \texttt{timeave} w/MNC  \\
106          \texttt{autodiff\_mnc}  &  L  & \texttt{.FALSE.}  &  
107          write \texttt{autodiff} w/MNC  \\\hline
108        \end{tabular}
109      }
110    \end{center}
111    
112    Additional MNC--related parameters are contained within the main
113    \texttt{data} namelist file and in some of the namelist files for
114    individual packages.  These options are:
115    \begin{center}
116      {\footnotesize
117        \begin{tabular}[htb]{|l|c|l|l|}\hline
118          \textbf{Name}  &  \textbf{T}  &  
119          \textbf{Default}  &  \textbf{Description}  \\\hline
120          \multicolumn{4}{|c|}{\ }  \\
121          \multicolumn{4}{|c|}{Main namelist file:
122            ``\textbf{data}''}  \\\hline
123          \texttt{snapshot\_ioinc}  &  L  & \texttt{.FALSE.}  &  
124          write \texttt{snapshot} ``inclusively''  \\
125          \texttt{timeave\_ioinc}  &  L  & \texttt{.FALSE.}  &  
126          write \texttt{timeave} ``inclusively''  \\
127          \texttt{monitor\_ioinc}  &  L  & \texttt{.FALSE.}  &  
128          write \texttt{monitor} ``inclusively''  \\
129          \texttt{the\_run\_name}  &  C  & ``name...''  &  
130          name is included in all MNC output  \\\hline
131          \multicolumn{4}{|c|}{\ }  \\
132          \multicolumn{4}{|c|}{Diagnostics namelist file:
133            ``\textbf{data.diagnostics}''}  \\\hline
134          \texttt{diag\_mnc}  &  L  & \texttt{.FALSE.}  &  
135          write \texttt{diagnostics} w/MNC  \\
136          \texttt{diag\_ioinc}  &  L  & \texttt{.FALSE.}  &  
137          write \texttt{diagnostics} ``inclusively''  \\\hline
138        \end{tabular}
139      }
140    \end{center}
141    
142    By default, turning on MNC for a particular output type will result in
143    turning off all the corresponding (usually, default) MDSIO or STDOUT
144    output mechanisms.  In other words, output defaults to being an
145    exclusive selection.  To enable multiple kinds of simultaneous output,
146    flags of the form \texttt{NAME\_ioinc} have been created where
147    \texttt{NAME} corresponds to the various MNC output flags.  When a
148    \texttt{NAME\_ioinc} flag is set to \texttt{.TRUE.}, then multiple
149    simultaneous forms of output are allowed for the \texttt{NAME} output
150    mechanism.  The intent of this design is that typical users will only
151    want one kind of output while people debugging the code (particularly
152    the I/O routines) may want simultaneous types of output.
153    
154    This ``inclusive'' versus ``exclusive'' design is easily applied in
155    cases where three or more kinds of output may be generated.  Thus, it
156    can be readily extended to additional new output types (eg. HDF5).
157    
158  \subsection{Introduction}  Input types are always exclusive.
159    
160  The MNC package is a set of convenience routines written to expedite  \subsubsection{MNC Output}
 the process of creating, appending, and reading NetCDF files.  NetCDF  
 is a self-describing file format \cite{rew:97} intended primarily for  
 scientific data.  NetCDF reference papers, user guides, FAQs, and other  
 information can be obtained from UCAR's web site at:  
   
 \begin{itemize}  
 \item http://www.unidata.ucar.edu/packages/netcdf/  
 \end{itemize}  
161    
162    While NetCDF files are supposed to be ``self-describing'', it is
163    helpful to note the following:
164    
165    \begin{itemize}
166    \item The constraints placed upon the ``unlimited'' (or ``record'')
167      dimension inherent with NetCDF v3.x make it very inefficient to put
168      variables written at potentially different intervals within the same
169      file.  For this reason, MNC output is split into a few file ``base
170      names'' which try to reflect the nature of their content.
171      
172    \item All MNC output is currently done in a ``tile-per-file'' fashion
173      since most NetCDF v3.x implementions cannot write safely within MPI
174      or multi-threaded environments.  This tiling is done in a global
175      fashion and the tile numbers are appended to the base names
176      described above.  Some scripts to ``assemble'' output are available
177      (\texttt{MITgcm/utils/matlab}).  More general manipulations can be
178      accomplished with the
179      \begin{rawhtml}
180        <A href="http://nco.sourceforge.net">
181      \end{rawhtml}
182    \begin{verbatim}
183    NetCDF Operators (or ``NCO'') at http://nco.sourceforge.net
184    \end{verbatim}
185      \begin{rawhtml} </A> \end{rawhtml}
186      which is a very powerful and convenient set of tools for working
187      with all NetCDF files.
188      
189    \item On many systems, NetCDF has practical file size limits on the
190      order of 2--4GB (the maximium memory addressable with 32bit
191      pointers) due to a lack of operating system, compiler, and/or
192      library support.  In cases where this limit is reached, it is
193      generally a good idea to reduce write frequencies or restart from
194      pickups.
195      
196    \item MNC does not (yet) provide a mechanism for reading information
197      from a single ``global'' file as can be done with the MDSIO
198      package.  This is in progress.
199    
200    \end{itemize}
201    
 \subsection{Key Routines}  
202    
203    \subsection{MNC Internals}
204    
205    The \texttt{mnc} package is a two-level convenience library (or
206    ``wrapper'') for most of the NetCDF Fortran API.  Its purpose is to
207    streamline the user interface to NetCDF by maintaining internal
208    relations (look-up tables) keyed with strings (or names) and entities
209    such as NetCDF files, variables, and attributes.
210    
211    The two levels of the \texttt{mnc} package are:
212    \begin{description}
213    
214    \item[Upper level] \
215      
216      The upper level contains information about two kinds of
217      associations:
218      \begin{description}
219      \item[grid type] is lookup table indexed with a grid type name.
220        Each grid type name is associated with a number of dimensions, the
221        dimension sizes (one of which may be unlimited), and starting and
222        ending index arrays.  The intent is to store all the necessary
223        size and shape information for the Fortran arrays containing
224        MITgcm--style ``tile'' variables (that is, a central region
225        surrounded by a variably-sized ``halo'' or exchange region as
226        shown in Figures \ref{fig:communication_primitives} and
227        \ref{fig:tiling-strategy}).
228      
229      \item[variable type] is a lookup table indexed by a variable type
230        name.  For each name, the table contains a reference to a grid
231        type for the variable and the names and values of various
232        attributes.
233      \end{description}
234      
235      Within the upper level, these associations are not permanently tied
236      to any particular NetCDF file.  This allows the information to be
237      re-used over multiple file reads and writes.
238    
239    \item[Lower level] \
240      
241      In the lower (or internal) level, associations are stored for NetCDF
242      files and many of the entities that they contain including
243      dimensions, variables, and global attributes.  All associations are
244      on a per-file basis.  Thus, each entity is tied to a unique NetCDF
245      file and will be created or destroyed when files are, respectively,
246      opened or closed.
247    
248    \end{description}
249    
250    
251    \subsubsection{MNC Grid--Types and Variable--Types}
252    
253    As a convenience for users, the MNC package includes numerous routines
254    to aid in the writing of data to NetCDF format.  Probably the biggest
255    convenience is the use of pre-defined ``grid types'' and ``variable
256    types''.  These ``types'' are simply look-up tables that store
257    dimensions, indicies, attributes, and other information that can all
258    be retrieved using a single character string.
259    
260    The ``grid types'' are a way of mapping variables within MITgcm to
261    NetCDF arrays.  Within MITgcm, most spatial variables are defined
262    using two-- or three--dimensional arrays with ``overlap'' regions (see
263    Figures \ref{fig:communication_primitives}, a possible vertical index,
264    and \ref{fig:tiling-strategy}) and tile indicies such as the following
265    ``U'' velocity:
266    \begin{verbatim}
267          _RL  uVel (1-OLx:sNx+OLx,1-OLy:sNy+OLy,Nr,nSx,nSy)
268    \end{verbatim}
269    as defined in \filelink{model/inc/DYNVARS.h}{model-inc-DYNVARS.h}
270    
271    The grid type is a character string that encodes the presence and
272    types associated with the four possible dimensions.  The character
273    string follows the format
274    \begin{center}
275      \texttt{H0\_H1\_H2\_\_V\_\_T}
276    \end{center}
277    where the terms \textit{H0}, \textit{H1}, \textit{H2}, \textit{V},
278    \textit{T} can be almost any combination of the following:
279    \begin{center}
280      \begin{tabular}[h]{|ccc|c|c|}\hline
281        \multicolumn{3}{|c|}{Horizontal} & Vertical & Time \\
282        \textbf{H0}: location & \textbf{H1}: dimensions & \textbf{H2}: halo
283              & \textbf{V}: location & \textbf{T}: level  \\\hline
284        \texttt{-} & xy & Hn & \texttt{-} & \texttt{-} \\
285        U  &  x  &  Hy  &  i  &  t  \\
286        V  &  y  &      &  c  &     \\
287        Cen  &   &      &     &     \\
288        Cor  &   &      &     &     \\\hline
289      \end{tabular}
290    \end{center}
291    A example list of all pre-defined combinations is contained in the
292    file
293    \begin{center}
294      \texttt{pkg/mnc/pre-defined\_grids.txt}.
295    \end{center}
296    
297    The variable type is an association between a variable type name and the
298    following items:
299    \begin{center}
300      \begin{tabular}[h]{|l|l|}\hline
301        \textbf{Item}  & \textbf{Purpose}  \\\hline
302        grid type  &  defines the in-memory arrangement  \\
303        \texttt{bi,bj} dimensions  &  tiling indices, if present  \\\hline
304      \end{tabular}
305    \end{center}
306    and is used by the \texttt{mnc\_cw\_*\_[R|W]} subroutines for reading
307    and writing variables.
308    
309    
310    \subsubsection{Using MNC: Examples}
311    
312    Writing variables to NetCDF files can be accomplished in as few as two
313    function calls.  The first function call defines a variable type,
314    associates it with a name (character string), and provides additional
315    information about the indicies for the tile (\texttt{bi},\texttt{bj})
316    dimensions.  The second function call will write the data at, if
317    necessary, the current time level within the model.
318    
319    Examples of the initialization calls can be found in the file
320    \filelink{model/src/ini\_mnc\_io.F}{model-src-ini_mnc_io.F}
321    where these function calls:
322    {\footnotesize
323    \begin{verbatim}
324    C     Create MNC definitions for DYNVARS.h variables
325          CALL MNC_CW_ADD_VNAME('iter', '-_-_--__-__t', 0,0, myThid)
326          CALL MNC_CW_ADD_VATTR_TEXT('iter',1,
327         &     'long_name','iteration_count', myThid)
328    
329          CALL MNC_CW_ADD_VNAME('model_time', '-_-_--__-__t', 0,0, myThid)
330          CALL MNC_CW_ADD_VATTR_TEXT('model_time',1,
331         &     'long_name','Model Time', myThid)
332          CALL MNC_CW_ADD_VATTR_TEXT('model_time',1,'units','s', myThid)
333    
334          CALL MNC_CW_ADD_VNAME('U', 'U_xy_Hn__C__t', 4,5, myThid)
335          CALL MNC_CW_ADD_VATTR_TEXT('U',1,'units','m/s', myThid)
336          CALL MNC_CW_ADD_VATTR_TEXT('U',1,
337         &     'coordinates','XU YU RC iter', myThid)
338    
339          CALL MNC_CW_ADD_VNAME('T', 'Cen_xy_Hn__C__t', 4,5, myThid)
340          CALL MNC_CW_ADD_VATTR_TEXT('T',1,'units','degC', myThid)
341          CALL MNC_CW_ADD_VATTR_TEXT('T',1,'long_name',
342         &     'potential_temperature', myThid)
343          CALL MNC_CW_ADD_VATTR_TEXT('T',1,
344         &     'coordinates','XC YC RC iter', myThid)
345    \end{verbatim}
346    }
347    {\noindent initialize four \texttt{VNAME}s and add one or more NetCDF
348      attributes to each.}
349        
350    The four variables defined above are subsequently written at specific
351    time steps within
352    \filelink{model/src/write\_state.F}{model-src-write_state.F}
353    using the function calls:
354    {\footnotesize
355    \begin{verbatim}
356    C       Write dynvars using the MNC package
357            CALL MNC_CW_SET_UDIM('state', -1, myThid)
358            CALL MNC_CW_I_W('I','state',0,0,'iter', myIter, myThid)
359            CALL MNC_CW_SET_UDIM('state', 0, myThid)
360            CALL MNC_CW_RL_W('D','state',0,0,'model_time',myTime, myThid)
361            CALL MNC_CW_RL_W('D','state',0,0,'U', uVel, myThid)
362            CALL MNC_CW_RL_W('D','state',0,0,'T', theta, myThid)
363    \end{verbatim}
364    }
365    
366    While it is easiest to write variables within typical 2D and 3D fields
367    where all data is known at a given time, it is also possible to write
368    fields where only a portion (\textit{eg.} a ``slab'' or ``slice'') is
369    known at a given instant.  An example is provided within
370    \filelink{pkg/mom\_vecinv/mom\_vecinv.F}{pkg-mom_vecinv-mom_vecinv.F}
371    where an offset vector is used: {\footnotesize
372    \begin{verbatim}
373           IF (useMNC .AND. snapshot_mnc) THEN
374             CALL MNC_CW_RL_W_OFFSET('D','mom_vi',bi,bj, 'fV', uCf,
375       &          offsets, myThid)
376             CALL MNC_CW_RL_W_OFFSET('D','mom_vi',bi,bj, 'fU', vCf,
377       &          offsets, myThid)
378           ENDIF
379    \end{verbatim}
380    }
381    to write a 3D field one depth slice at a time.
382    
383    Each element in the offset vector corresponds (in order) to the
384    dimensions of the ``full'' (or virtual) array and specifies which are
385    known at the time of the call.  A zero within the offset array means
386    that all values along that dimension are available while a positive
387    integer means that only values along that index of the dimension are
388    available.  In all cases, the matrix passed is assumed to start (that
389    is, have an in-memory structure) coinciding with the start of the
390    specified slice.  Thus, using this offset array mechanism, a slice
391    can be written along any single dimension or combinations of
392    dimensions.
393    
 \subsection{References}  

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