Feature/deim

[jbwahl]

• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes?
• Have you successfully run the Feel++ testsuite with your changes locally?
• Have you written Doxygen comments in your contribution?

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Last development in DEIM framework:

• fix Deadlock in DEIM using linftyNorm for vectors #1058, using linftyNorm()
• close DEIM : add options to store Tensors during greedy #1048 : use options --deim.store-vectors=true and --deim.store-matrices=true to store tensors during DEIM/MDEIM greedy algorithm.
• close DEIM : add option to store solutions on disk (NL problems) #1047 : during greedy algorithm, nl-solutions are written on disk if option --deim.elements.write=true. The storing directory can be specified using --deim.elements.directory=<path>. This directory is cleaned after greedy if options --deim.elements.clean-directory=true
• close Effective online phase for DEIM #974: we now have an interpolation model for the online phase. Also work for composite spaces, thanks to the new class : TwoSpacesMap which provides a map between a parallel space and a sequential space (on a submesh). see d29c7f0
• close Support smart storage/replay of offline eim/deim data #866 : DEIM can be reloaded from database. The tensors are not stored but rebuilt from saved value of mu_m.
• close Add support for DEIM #925 : DEIM is now fully operational

[jbwahl]

@romainhild @vincentchabannes I am done with that feature.
If everything is ok for both of you, we can merge.

[jbwahl]

This merge will close #925 and close #974 close #866

[prudhomm]

@jbwahl could you edit the description and add the list of issues this PR is dealing with ?
thanks in advance

[jbwahl]

@prudhomm is description ok for you ?

[jbwahl]

@prudhomm all good here. Ready to merge.