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'''Author''' : jenniewaters

'''ticket''' : #1464

'''Branch''' : [https://forge.ipsl.jussieu.fr/nemo/browser/branches/2015/dev_r5776_UKMO2_OBS_efficiency_improvs  dev_r5776_UKMO2_OBS_efficiency_improvs ] 
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=== Description ===
This branch has been created for developments to the observation operator to improve memory use. The observations operator uses global arrays and this causes memory inefficiencies when NEMO is run on a large number of processors. This is a particular obstacle for high resolution models such as ORCA12. The proposed changes remove any calls to global arrays when ln_grid_global=.FALSE.. Note that global arrays are still used if ln_grid_global=.TRUE. as this would require a much more extensive re-write of the code.

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

||SETTE Tested|| YES ||
||Other model configurations|| YES ||
||Processor configurations tested||[ 2 by 8] and [4 by 4 ]||
||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|| YES - see below for full details.||

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

'Please add further summary details here'

 * Processor configurations tested
 * etc----

=== Bit Comparability ===
||Does this change preserve answers in your tested standard configurations (to the last bit) ?||!'''YES/NO !'''||
||Does this change bit compare across various processor configurations. (1xM, Nx1 and MxN are recommended)||!'''YES/NO!'''||
||Is this change expected to preserve answers in all possible model configurations?||!'''YES/NO!'''||
||Is this change expected to preserve all diagnostics? [[BR]]!,,!''Preserving answers in model runs does not necessarily imply preserved diagnostics. !''||!'''YES/NO!'''||

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?||!'''YES/NO !'''||
||Does your change require a change in compiler options?||!'''YES/NO !'''||

If any of these apply, please document the changes required here.......

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

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=== IPR issues ===
||Has the code been wholly (100%) produced by NEMO developers staff working exclusively on NEMO?||!'''YES/ NO !'''||

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..........