Commits on Oct 23, 2024

1. Refactor of vertical reconstruction with six new schemes …

   This refactor is motivated by i) adding a set of new reconstructions schemes
   that are ready-to-use-now for remapping, but ii) will be an essential part of a
   new grid generator that will use some of the new member methods available only
   as a result of the refactor. The "refactor" actually duplicates many existing
   schemes, leaving the original code in place to provide a period of transition
   just in case there's some major reason to revert to the old style of code.
   
   What changed
   ============
   - removed remapping_attic.F90
   - added 16 modules name Recon1d_*.F90, which extend a base Recon1d_type.F90
   - MOM_remapping.F90
     - rewrote remapping_unit_tests to be tidier
     - added tests for
       1) invariance when remapping to/from the same grid;
       2) preservation of a uniform value (many of the old schemes fail);
       3) internal consistency such as monotonic ordering of values at
          edges, no internal extrema, etc., but only for the new Recon1d_* schemes.
   - added more schemes to config_src/drivesr/timing_tests/time_MOM_remapping.F90
   - added documentation via _Vertical_Reconstruction.dox with references
   
   Six new schemes are added: C_PLM_CW, C_PLM_CWK, C_MPLM_CWK, C_EMPLM_CWK,
   C_PPM_CWK, and C_EPPM_CWK.
   
   Ten existing schemes were ported to the new class, along with their
   non-monotonic behaviors or ill-formed expressions.  Others can be ported later
   if needed, although one result of the refactor was the discovery that none of
   the existing schemes worked as desired.
   
   The new form uses a class (Recon1d) to define a uniform API for all the
   reconstruction schemes. The methods of the class include:
   - init() that creates work arrays and stores parameters such as `h_neglect`
   - reconstruct() that causes the reconstruction parameters to be calculated
   - average() that returns the average between two points in a reconstruction
     (used in the remap_src_to_sub_grid() functions)
   - unit_tests() method
   - check_reconstruction() checks that a reconstruction has the
     properties that it should (e.g. reconstruction values are monotonic)
     Theses properties are defined by each scheme, although many are shared
     between schemes.
   - f() that evaluates the reconstruction at a point (this will be used in the
     new grid-generator).
   - dfdx() that evaluates the derivative of the reconstruction at a point (this
     will be used in the new grid-generator)
   
   Testing
   =======
   
   New tests have been added that check uniform states are preserved, states are
   preserved under unchanging grid, and that the reconstructions are internally
   consistent according to their own definition. This last is only available for
   the new class-based schemes via the check_reconstruction() method which can be
   customized to each reconstruction, which allows us to document which properties
   (e.g. monotonicity) are satisfied and which are not.  These new tests use
   seeded random numbers which has proven useful for debugging/development, but
   are not necessarily useful in the CI. Nevertheless, I've made it part of
   remapping_unit_tests() so there is a template for debugging/testing new schemes
   when we add them. The same sequence of random numbers is used for each scheme,
   but the numbers are compiler dependent so the documented "fails" record the
   compiler version in comments.
   
   The base Recon1d class also provides a second type to make testing convenient.
   In time, this could (should) be moved out to a stand-alone module, so long as
   it does not become cumbersome. Currently this type is hidden to avoid expanding
   the network of dependencies, particularly using anything in the `framework/`
   directory which is not needed by the class.
   
   Performance
   ===========
   - the new class-based schemes are all faster than their counterparts in the
     original code style;
   - example numbers can be found in the build-test-perfmon job  of this commit
     (expand the "Display timing results");
   - e.g. timings for PPM_HYBGEN and C_PPM_HYBGEN show a marginal (~10%) speed
     up due to code style, and C_PPM_CWK has a more substantial speed up (~20%)
     due to a lighter algorithm;
   - I imagine we will see further speed ups if we worked on arrays rather than
     columns, which is an extension that could be implemented later.
   
   Documentation
   =============
   - the new module APIs are documented;
   - a new page, `_Vertical_Reconstruction.dox`, details the vertical
     reconstruction schemes, tabulates the values of `REMPAPPING_SCHEME`,
     and summarize some properties.
   
   Minor (unrelated)
   =================
   - removed `-j` for nested make in `.testing/Makefile`

   

   adcroft committed Oct 23, 2024
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