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'''Author''' : Ed Blockley

'''ticket''' : #871

'''Branch''' : [https://forge.ipsl.jussieu.fr/nemo/browser/branches/2011/dev_r2802_UKMET3_rebuild   dev_r2802_UKMET3_rebuild] 
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=== Description ===


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=== Testing ===
Testing could consider (where appropriate) other configurations in addition to NVTK].

||NVTK Tested||!'''N/A!'''||
||Other model configurations||!'''YES!'''||
||Processor configurations tested||[ 4*8, 8*4, 5*6, 8*12, 8*16 ]||
||If adding new functionality please confirm that the [[BR]]New code doesn't change results when it is switched off [[BR]]and !''works!'' when switched on||!'''N/A!'''||

(Answering UNSURE is likely to generate further questions from reviewers.)

'Please add further summary details here'

 * The rebuild code is a stand-alone code and does not impact on any existing NEMO configurations
 * It has however been tested by rebuilding files on many different processor configurations as detailed in the table above
 * The OMP parallelisation has been tested by running with many different numbers of threads - all of which bit compare
 * The code has been tested with many different types of file including vn3.2 restart files, vn3.2 diagnostics, vn3.3.1 diagnostics

=== Bit Comparability ===
||Does this change preserve answers in your tested standard configurations (to the last bit) ?||!'''YES !'''||
||Does this change bit compare across various processor configurations. (1xM, Nx1 and MxN are recommended)||!'''YES!'''||
||Is this change expected to preserve answers in all possible model configurations?||!'''YES!'''||
||Is this change expected to preserve all diagnostics? [[BR]]!,,!''Preserving answers in model runs does not necessarily imply preserved diagnostics. !''||!'''YES!'''||

If you answered !'''NO!''' to any of the above, please provide further details:

 * Which routine(s) are causing the difference?
 * Why the changes are not protected by a logical switch or new section-version
 * What is needed to achieve regression with the previous model release (e.g. a regression branch, hand-edits etc). If this is not possible, explain why not.
 * What do you expect to see occur in the test harness jobs?
 * Which diagnostics have you altered and why have they changed?Please add details here........

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=== System Changes ===
||Does your change alter namelists?||!'''NO !'''||
||Does your change require a change in compiler options?||!'''YES!'''||

If any of these apply, please document the changes required here.......
 * The rebuild uses its own namelist (nam_rebuild) but this is very simple and can be constructed on the fly by the rebuild_nemo script
 * In order to use OMP optimisations compile options will need to be changed - for this I shall create _omp specific compile configs in https://forge.ipsl.jussieu.fr/nemo/browser/trunk/NEMOGCM/ARCH/

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=== Resources ===
!''Please !''summarize!'' any changes in runtime or memory use caused by this change......!''

This rebuild is considerably faster than the IOIPSL rebuild but does use a little more memory.
However the memory requirements can be reduced by using the 'time-chunking' functionality which splits 4D variables up into chunks over the record (4th) dimension.

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=== IPR issues ===
||Has the code been wholly (100%) produced by NEMO developers staff working exclusively on NEMO?||!'''YES!'''||

If No:

 * Identify the collaboration agreement details
 * Ensure the code routine header is in accordance with the agreement, (Copyright/Redistribution etc).Add further details here if required..........