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\subsection{Using MNC} |
\subsection{Using MNC} |
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|
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\subsubsection{MNC Configuration and Inputs} |
\subsubsection{MNC Configuration} |
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|
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As with all MITgcm packages, MNC can be turned on/off at compile time |
As with all MITgcm packages, MNC can be turned on or off at compile time |
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using the \texttt{packages.conf} file or the genmake2 |
using the \texttt{packages.conf} file or the \texttt{genmake2} |
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\texttt{-enable=mnc} or \texttt{-disable=mnc} switches. |
\texttt{-enable=mnc} or \texttt{-disable=mnc} switches. |
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|
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While MNC is likely to work ``as is'', there are a few compile--time |
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constants that may need to be increased for simulations that employ |
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large numbers of tiles within each process. Note that the important |
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quantity is the maximum number of tiles \textbf{per process}. Since |
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MPI configurations tend to distribute large numbers of tiles over |
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relatively large numbers of MPI processes, these constants will rarely |
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need to be increased. |
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|
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If MNC runs out of space within its ``lookup'' tables during a |
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simulation, then it will provide an error message along with a |
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recommendation of which parameter to increase. The parameters are all |
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located within \filelink{pkg/mnc/mnc\_common.h}{pkg-mnc-mnc_common.h} |
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and the ones that may need to be increased are: |
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|
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\begin{center} |
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{\footnotesize |
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\begin{tabular}[htb]{|l|r|l|}\hline |
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\textbf{Name} & |
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\textbf{Default} & \textbf{Description} \\\hline |
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& & \\ |
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\texttt{MNC\_MAX\_ID} & 1000 & |
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\textbf{IDs for various low-level entities} \\ |
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\texttt{MNC\_MAX\_INFO} & 400 & |
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\textbf{IDs (mostly for object sizes)} \\ |
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\texttt{MNC\_CW\_MAX\_I} & 150 & |
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\textbf{IDs for the ``wrapper'' layer} \\\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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In those rare cases where MNC ``out-of-memory'' error messages are |
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encountered, it is a good idea to increase the too-small parameter by |
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a factor of \textbf{2--10} in order to avoid wasting time on an |
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iterative compile--test sequence. |
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|
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|
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\subsubsection{MNC Inputs} |
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|
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For run-time configuration, most of the MNC--related model parameters |
For run-time configuration, most of the MNC--related model parameters |
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are contained within a Fortran namelist file called \texttt{data.mnc}. |
are contained within a Fortran namelist file called \texttt{data.mnc}. |
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If this file does not exist, then the MNC package will interpret that |
If this file does not exist, then the MNC package will interpret that |
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which is a very powerful and convenient set of tools for working |
which is a very powerful and convenient set of tools for working |
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with all NetCDF files. |
with all NetCDF files. |
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|
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\item On many systems, NetCDF has practical file size limits on the |
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order of 2--4GB (the maximium memory addressable with 32bit |
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pointers) due to a lack of operating system, compiler, and/or |
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library support. In cases where this limit is reached, it is |
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generally a good idea to reduce write frequencies or restart from |
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pickups. |
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|
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\item MNC does not (yet) provide a mechanism for reading information |
\item MNC does not (yet) provide a mechanism for reading information |
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from a single ``global'' file as can be done with the MDSIO |
from a single ``global'' file as can be done with the MDSIO |
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package. |
package. This is in progress. |
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|
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\end{itemize} |
\end{itemize} |
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