= Using AGRIF for embedded zooms in NEMO

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== Overview

AGRIF (Adapative Grid Refinement In Fortran) is a library that allows the seamless refinement of rectangular regions in NEMO. Activating AGRIF requires the cpp key "key_agrif" to be defined at compilation time. Although this is transparent to users, the way the code is processed during compilation is different from the standard case: a preprocessing stage (the so called "conv" program) translates the actual code so that saved arrays may be be switched in memory space from one domain to an other. 
An additional text file "AGRIF_FixedGrids.in" is also required at run time. This is where the grid hierarchy is defined. An example of such a file, here taken from the VORTEX test case, is given below: 
{{{
1
19 38 19 38 3 3 3
0
}}}
The first line indicates the number of zooms (1). The second line contains the starting and ending indexes in both directions on the root grid (19 38 19 38) followed by the space and time refinement factors (3 3 3). The last line is the number of child grid nested in the refined region (0). A more complex example with telescoping grids can be found in the AGRIF_DEMO reference configuration directory (NEMO 4.0 only).





Main features of AGRIF in NEMO, what can be done:

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== Available in the 3_6 revision of NEMO 
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=== AGRIF demonstrator in reference configuration

* The [wiki:Users/ReferenceConfigurations/ORCA2_LIM3_PISCES global reference configuration includes a demonstrator for using AGRIF in NEMO] 


== Available in the forthcoming 4.0
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In addition to the reference configurations in the 3_6 release, the [wiki:Users/Announcement_4.0.beta_release 4.0 beta release is now available] and includes new configurations and test cases with AGRIF, see below:
=== New reference configurations with AGRIF 

* AGRIF_DEMO ''to be described''

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=== New tests cases demonstrating some major features of AGRIF with NEMO:
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== AGRIF in NEMO documentation
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* general
* How to set up a new configuration
* ...