This was precisely the point of my example: if you embed the point after each
point is created, you force a rebuild of the topology of the model. So the
efficient script would be
SetFactory("OpenCASCADE");
Box(1) = {0,0,0, 1,1,1};
N=10000;
For i In {1:N}
Point(100+i) = {0.25 + 5e-5*i, 0.1,0.1};
EndFor
Point{100+1:100+N} In Volume{1};
Christophe
> On 31 Jan 2019, at 14:48, Al Sc <[email protected]> wrote:
>
> Dear Christophe,
>
> my example files are scientific data, however originate from processing
> certain proprietary 3D models that were shared with me under certain
> restrictions. Therefore, it's difficult to share my original file with you.
> However, I was indeed able to reproduce the issue using only a slight
> modification of your example file!
>
> Compare the following two files:
> test1.geo:
> %%% %%% %%% %%% %%% %%% %%% %%% %%% %%%
> SetFactory("OpenCASCADE");
> Box(1) = {0,0,0, 1,1,1};
> For i In {1:1000}
> Point(100+i) = {0.25 + 1e-4*i, 0.1,0.1};
> Point{100+i} In Volume{1};
> EndFor
> %%% %%% %%% %%% %%% %%% %%% %%% %%% %%%
>
> test2.geo:
> %%% %%% %%% %%% %%% %%% %%% %%% %%% %%%
> SetFactory("OpenCASCADE");
> Box(1) = {0,0,0, 1,1,1};
> For i In {1:10000}
> Point(100+i) = {0.25 + 1e-5*i, 0.1,0.1};
> Point{100+i} In Volume{1};
> EndFor
> %%% %%% %%% %%% %%% %%% %%% %%% %%% %%%
>
> The first file contains 1000 internal pts, and the second one contains 10
> times as much.
> Now run:
> $ time gmsh -1 test1.geo
> -> Takes 0.88 sec
> $ time gmsh -1 test2.geo
> -> Takes 75 sec
> This is a nearly 100 (!!!) times increase in parsing run time, when the model
> size is increased by only a factor of 10.
> This nicely illustrates what I meant by "quadratic growth of the parsing run
> time as a function of the number of internal pts."
> As a consequence of this "quadratic growth", the run time for larger models
> quickly becomes enormous.
>
> Best regards
>
> A.S.
>
> Am Do., 31. Jan. 2019 um 14:31 Uhr schrieb Christophe Geuzaine
> <[email protected]>:
>
> Can you send a test file?
>
> I tried this, i.e. adding 1000 embedded points in a volume, and it is quite
> fast (< 2 seconds):
>
> SetFactory("OpenCASCADE");
> Box(1) = {0,0,0, 1,1,1};
> For i In {1:1000}
> Point(100+i) = {0.25 + 5e-4*i, 0.1,0.1};
> Point{100+i} In Volume{1};
> EndFor
>
> Maybe you modify the model after each insertion of an embedded point, which
> would force a rebuild of the topological model?
>
> Christophe
>
>
> > On 31 Jan 2019, at 13:04, Al Sc <[email protected]> wrote:
> >
> > Dear Sir or Madam,
> >
> > some more details on the previously-reported case of extremely slow parsing
> > of a gmsh file:
> > The file contains 34795 points -- of which 23041 points are "Point In
> > Volume" (e.g. embedded_vertices of a GRegion?). Moreover, it contains 4998
> > "Plane Surface"s and one single "Volume". Almost all plane surfaces are
> > triangles and quads -- except for <10 facets, which each have a very high
> > vertex count (typ. 7000).
> >
> > I found out that if I remove all "Point In Volume" objects, then the
> > parsing takes only 20 seconds. However, if all the "Point In Volume"
> > objects are not removed, parsing takes around 3000 seconds. This led me to
> > the hypothesis that there is some huge inefficiency with parsing gmsh files
> > with "Point In Volume" (probably quadratic run time in N(PointInVolume)??).
> >
> > Furthermore, I analyzed the runs using "perf" (linux utility).
> > Run 1 (about 3000 seconds):
> > $ time perf record ./gmsh-3.0.6-Linux64/bin/gmsh -1 input_orig.geo
> > Run 2 (about 20 seconds):
> > $ time perf record ./gmsh-3.0.6-Linux64/bin/gmsh -1
> > input_no_point_in_volume.geo
> > In Run 1, "perf report" yields the following top-scoring functions:
> > 11.57% gmsh gmsh [.] GModel::getEdgeByTag
> > 7.73% gmsh gmsh [.] GEO_Internals::synchronize
> > 6.80% gmsh libc-2.12.so [.] _int_free
> > 6.31% gmsh gmsh [.] GModel::getVertexByTag
> > 4.91% gmsh libc-2.12.so [.] malloc
> > 4.53% gmsh gmsh [.] InterpolateCurve
> > 4.40% gmsh libstdc++.so.6.0.22 [.] std::_Rb_tree_increment
> > 3.88% gmsh libc-2.12.so [.] memcpy
> > 3.69% gmsh gmsh [.] List_Nbr
> > 3.35% gmsh libc-2.12.so [.] _int_malloc
> > 3.24% gmsh gmsh [.] GEntity::GEntity
> > 3.13% gmsh gmsh [.] avl_lookup
> > 2.63% gmsh gmsh [.] gmshFace::resetNativePtr
> > 2.53% gmsh gmsh [.] GEdge::addFace
> > 2.52% gmsh gmsh [.] CompareVertex
> > 1.97% gmsh gmsh [.] std::_List_base<GEdge*,
> > std::allocator<GEdge*>
> > 1.88% gmsh gmsh [.] GModel::getFaceByTag
> > 1.76% gmsh gmsh [.] Tree_Action
> > 1.74% gmsh gmsh [.] gmshEdge::degenerate
> > 1.63% gmsh gmsh [.] CompareCurve
> > 1.53% gmsh gmsh [.] std::_List_base<int,
> > std::allocator<int> >::_M
> > 1.38% gmsh gmsh [.] GModel::deletePhysicalGroups
> > 1.23% gmsh gmsh [.] std::_List_base<GEdgeSigned,
> > std::allocator<GE
> > 1.10% gmsh gmsh [.] GVertex::addEdge
> > 0.85% gmsh gmsh [.] List_Read
> > 0.75% gmsh gmsh [.] GEdge::getBeginVertex
> > 0.73% gmsh gmsh [.] GFace::computeMeanPlane
> > 0.73% gmsh libc-2.12.so [.] free
> > 0.67% gmsh gmsh [.] CTX::instance
> > 0.65% gmsh gmsh [.] gmshEdge::resetMeshAttributes
> >
> > This suggests that maybe GModel::getEdgeByTag is eventually called a
> > quadratic number of times in the number of PointInVolume-objects -- and
> > this causes the drastic slow-down.
> >
> > Could you please investigate this? Thanks a lot!
> > (As already mentioned, this issue also occurs with gmsh-4.x.x)
> >
> > Best regards
> > A. S.
> > _______________________________________________
> > gmsh mailing list
> > [email protected]
> > http://onelab.info/mailman/listinfo/gmsh
>
> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
>
>
—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
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