[bug] Fix stable fluid BFECC advection #1764

Eydcao · 2020-08-24T06:18:05Z

Related issue = #1757

In this PR I plan to fix the BFECC advection in stable_fluid.py. Seems that there are several problems tangled inside this one. So let's try to solve them one-by-one. I may need your @yuanming-hu and @archibate help to review if the errors are from the BFECC or the PPE solving. Thanks a lot,

Fixed the correction term's symbol.
Reset Poisson solver to jacobi_single.
Fixed the whole advect_bfecc function.
Fixed the int() (with math.floor()) which irritates when input is negative

[Click here for the format server]

…d return to use jacobii_single

codecov · 2020-08-24T07:11:25Z

Codecov Report

Merging #1764 into master will decrease coverage by 0.84%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1764      +/-   ##
==========================================
- Coverage   43.42%   42.58%   -0.85%     
==========================================
  Files          44       44              
  Lines        6010     6185     +175     
  Branches     1041     1072      +31     
==========================================
+ Hits         2610     2634      +24     
- Misses       3249     3397     +148     
- Partials      151      154       +3

Impacted Files	Coverage Δ
python/taichi/lang/__init__.py	`42.44% <0.00%> (-11.16%)`	⬇️
python/taichi/lang/impl.py	`64.50% <0.00%> (-0.73%)`	⬇️
python/taichi/main.py	`23.03% <0.00%> (-0.54%)`	⬇️
python/taichi/lang/matrix.py	`64.73% <0.00%> (-0.30%)`	⬇️
python/taichi/lang/ops.py	`43.89% <0.00%> (-0.19%)`	⬇️
python/taichi/testing.py	`78.12% <0.00%> (ø)`
python/taichi/misc/gui.py	`0.00% <0.00%> (ø)`
python/taichi/misc/image.py	`41.26% <0.00%> (+0.09%)`	⬆️
python/taichi/lang/common_ops.py	`69.26% <0.00%> (+0.21%)`	⬆️
python/taichi/lang/expr.py	`61.95% <0.00%> (+0.28%)`	⬆️
... and 2 more

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…ce back

examples/stable_fluid.py

archibate · 2020-08-25T15:02:09Z

examples/stable_fluid.py

+        intermedia_qf[i, j] = bilerp(qf, p)
+
+    ti.cache_read_only(intermedia_qf, qf, vf)
+    for i, j in vf:


Is the key problem about separating bfecc to two offload?

Yes. To be more precise, we need a forward advection (backtrack + interpolate) to get an inter-media quantity field first, then a backward advection to (backtrace in -dt direction + interpolate) to get the field at the original time stamp (assuming there is no error). Finally, we got the error and fix the inter-media field.

Since for the second one (backward advection) we need the whole inter-media field ready, it's necessary to run it in a separate another loop and store it already.

But to be noticed, jacobbi_dual caused serious artifacts with the new bfecc.

I will post detailed comparisons between combination of different methods when I get a minute.

examples/stable_fluid.py

Co-authored-by: 彭于斌 <1931127624@qq.com>

Eydcao · 2020-08-26T14:26:11Z

Comparison List:

Old bfecc

New bfecc with jacobi_dual

New bfecc with jacobi_single

Eydcao · 2020-08-26T14:58:43Z

New bfecc with mgpcg

This is super interesting~@archibate

archibate · 2020-08-26T15:37:09Z

Thanks for all the hard work here! I think I found the reason now.

Eydcao · 2020-08-26T16:36:42Z

After fixing the irrigating int() issue in interpolation, the boundary artifact is gone. And the new bfecc works nicely with jacobi_single. As the jacobi_double or mgpcg concerns other issues in PPE solving, I will leave them there to solve :)

Will organize and make it ready for review

examples/stable_fluid.py

Eydcao · 2020-08-26T16:46:52Z

examples/stable_fluid.py

@@ -326,6 +338,9 @@ def reset():
    dyes_pair.cur.fill(0)


+v_mngr = ti.VideoManager('./', framerate=24, automatic_build=False)
+


Suggested change

Eydcao · 2020-08-26T16:47:05Z

examples/stable_fluid.py

@@ -326,6 +338,9 @@ def reset():
    dyes_pair.cur.fill(0)


+v_mngr = ti.VideoManager('./', framerate=24, automatic_build=False)
+
+


Suggested change

examples/stable_fluid.py

archibate · 2020-08-26T16:53:35Z

Please do not use apply suggestions for large modification, always keep in mind that all our actions on GitHub will be sent into
322 people's mailbox. See https://github.com/taichi-dev/taichi/watchers.

apply known fixings, fix the bfecc process, the correction symbol, an…

3e0da34

…d return to use jacobii_single

Eydcao added 2 commits August 25, 2020 16:46

[skip ci] add standard test; fix some mistakes

34de871

[skip ci] remove the abundont '+0.5'; adjust the boundary to non-boun…

808c52c

…ce back

archibate reviewed Aug 25, 2020

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yuanming-hu changed the title ~~[bug] stable fluid's bfecc advection~~ [bug] Stable fluid's bfecc advection Aug 26, 2020

Eydcao commented Aug 26, 2020

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Apply suggestions from code review

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Co-authored-by: 彭于斌 <1931127624@qq.com>

archibate mentioned this pull request Aug 26, 2020

[Example] Fix stable_fluid.py boundary broken: int -> ti.floor, and make mpm3d.py 3x faster on CUDA #1784

Merged

[skip ci] apply suggestions from Yubin concerning floor and int

0fd590f

[skip ci] clean

ede5c88

Eydcao marked this pull request as ready for review August 26, 2020 16:44

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Eydcao requested a review from archibate August 28, 2020 05:24

yuanming-hu approved these changes Sep 26, 2020

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yuanming-hu changed the title ~~[bug] Stable fluid's bfecc advection~~ [bug] Fix stable fluid's BFECC advection Sep 26, 2020

yuanming-hu changed the title ~~[bug] Fix stable fluid's BFECC advection~~ [bug] Fix stable fluid BFECC advection Sep 26, 2020

yuanming-hu merged commit 206304e into taichi-dev:master Sep 26, 2020

yuanming-hu mentioned this pull request Sep 26, 2020

[release] v0.6.37 #1900

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[bug] Fix stable fluid BFECC advection #1764

[bug] Fix stable fluid BFECC advection #1764

Eydcao commented Aug 24, 2020 •

edited

codecov bot commented Aug 24, 2020 •

edited

archibate Aug 25, 2020

Eydcao Aug 26, 2020 •

edited

Eydcao Aug 26, 2020

Eydcao commented Aug 26, 2020

Eydcao commented Aug 26, 2020

archibate commented Aug 26, 2020

Eydcao commented Aug 26, 2020

Eydcao Aug 26, 2020

Eydcao Aug 26, 2020

archibate commented Aug 26, 2020

		@@ -326,6 +338,9 @@ def reset():
		dyes_pair.cur.fill(0)


		v_mngr = ti.VideoManager('./', framerate=24, automatic_build=False)

[bug] Fix stable fluid BFECC advection #1764

[bug] Fix stable fluid BFECC advection #1764

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