Cartesian Biweekly 2020 08 03

Action Points

Review of action points of last meeting:

[x] Complete Doodle poll:
- https://doodle.com/poll/zn2nhrv46et9hiem
[ ] Submit items for mini-workshop in this document:
- https://docs.google.com/document/d/1hFQ0TfO7fAiz7Xh-LE3RQucesI_k0tuCGku6pmz9qnY/edit
[x] Review Region GDP in light of figure discussion
[x] Schedule a meeting to discuss before next instance of this meeting
[x] Characterize minimum stencil overhead
[x] Add absolute indexing and offset-center writes to the list of items in the GTScript syntax workshop
[x] Select examples for off-center (vertically) writes
[x] Check whether no-check functionality already in StencilObject
[x] Determine best way to share meeting notes — prefer a single link
[x] Convention for GT4Py issue submission — will iterate
[x] Present results of student projects that @Oli F and @Tobias W are working on — deadline is Aug 7 16 - present on 18th

Rhea will file an issue to share off-center write examples
Johann will review the two ideas for regions and resolve differences
Enrique will add ideas to the syntax workshop

Discussion Points

Review PRs, please!

1. Keep PRs as drafts until they are ready for review
2. Assign someone - may be re-assigned as necessary

Ready for review

• Reduce overhead - https://github.com/GridTools/gt4py/pull/117
• Add BOOL - https://github.com/GridTools/gt4py/pull/129
• Math functions - https://github.com/GridTools/gt4py/pull/125

Needs a test

• Dawn extent fix - https://github.com/GridTools/gt4py/pull/101

Interesting new issues

• Scalars become temporary fields - https://github.com/GridTools/gt4py/issues/103
• Dimensions of temporaries - https://github.com/GridTools/gt4py/issues/107
• Determining type inside an if statement - https://github.com/GridTools/gt4py/issues/106
• Functions calls with scalar literals - https://github.com/GridTools/gt4py/issues/104

Dialect Workshop

• 18, 19, 21st August are best, but Matthias cannot join
• Reminder: add issues to the document
  • Directional offsets
  • Absolute k indexing
  • Named regions

Backend Compatibility

• Race condition PR in progress - https://github.com/GridTools/gt4py/pull/121

• Numpy backend warns about division by zero

  with computation(PARALLEL), interval(…):
  tmp = field[0,0,1]
  tmp2 = tmp + 1
  field = tmp2

    if __INLINED(flag):  
        tmp = field[1,0,0]  
        tmp2 = tmp + 1  
        field = tmp2  
  

End to End Tests

• Discuss ideas for how this could be structured

• Increase number of integration tests, or put them elsewhere?

• Existing types of tests: unit tests, code generation

• Do not make gt4py repo dependent on regression tests

• Eventually: mergeable/merged PRs should trigger dycore builds, and tests should be visible

• If we find problems, add reproducers as regressions tests

Regions

• Agreement on a lightweight splitter-based approach. Example:
  @gtscript.stencil(splitters={I: ['i0', 'ie'], J: ['j0', 'je']})
  def divergence_corner(...):
  from splitters import i0, ie, j0, je
  with computation(FORWARD), interval(...):
  uf = (u - 0.25*(va[0, -1, 0] + va)(cos_sg4[0, -1, 0] + cos_sg2)) \
  dyc0.5(sin_sg4[0, -1, 0] + sin_sg2)
  with region[i0 : i0 + 1, :], region[ie - 1 : ie, :]:
  uf = udyc0.5*(sin_sg4[0, -1, 0] + sin_sg2)

    vf = (v - 0.25*(ua[-1, 0, 0] + ua)*(cos_sg3[-1, 0, 0] + cos_sg1))  \  
                               *dxc*0.5*(sin_sg3[-1, 0, 0] + sin_sg1)  
    with region[:, j0 : j0 + 1], region[:, je - 1 : je]:  
      vf = v*dxc*0.5*(sin_sg3[-1, 0, 0] + sin_sg1)  
  
    divg_d = rarea_c * (vf[0, -1, 0] - vf + uf[-1, 0, 0] - uf)  
    with region[i0 : i0 + 1, j0 : j0 + 1], region[ie - 1 : ie, j0 : j0 + 1]:  
      divg_d = rarea_c * (-vf + uf[-1, 0, 0] - uf)  
    with region[i0 : i0 + 1, je - 1 : je], region[ie - 1 : ie, je - 1 : je]:  
      divg_d = rarea_c * (vf[0, -1, 0] + uf[-1, 0, 0] - uf)  
  

Review status of GDP3-Duck Storages

• Status update on the state of the GDP3 implementation including 1D/2D fields