Re: [deal.II] step-7 remarks on superconvergence and quadrature

[Praveen C]

I did this quick test in 2d for a Poisson problem

https://github.com/cpraveen/fembook/blob/master/deal.II/ex04/demo.cc 

(Change quadrature rules in this code as indicated below)

degree=1
assembly using QGauss(2)
error computed using QGauss(2)

cells   dofsL2 H1seminorm   
  1024   1089 1.606e-03- 2.517e-01- 
  4096   4225 4.015e-04 2.00 1.259e-01 1.00 
 16384  16641 1.004e-04 2.00 6.295e-02 1.00 
 65536  66049 2.510e-05 2.00 3.148e-02 1.00 
262144 263169 6.275e-06 2.00 1.574e-02 1.00 

We just observe the standard convergence rates, does not indicate 
superconvergence.

The following two also yield standard convergence rates

degree=1
assembly using QGauss(2)
error computed using QGaussLobatto(2)

degree=1
assembly using QGaussLobatto(2)
error computed using QGaussLobatto(2)

This indicates there is no superconvergence at the mesh vertices.

(In all cases above, the matrix is exactly assembled.)

Best
praveen

> On 07-Jul-2020, at 8:53 AM, Wolfgang Bangerth  wrote:
> 
> 
>> In step-7
>> https://www.dealii.org/current/doxygen/deal.II/step_7.html 
>> 
>> under section on "Verification of correctness”, there is this statement
>> *(e.g., for linear elements, do not use the QGauss(2) quadrature formula)*
>> because solution may exhibit superconvergence at the QGauss(2) points.
>> If we solve
>> -u’’ = 16*pi^2*sin(4*pi*x) in (0,1)
>> u(0) = 0, u(1) = 1
>> using 8 linear elements and QGauss(2) for quadrature.
>> The error is very small at the vertices of the mesh, not at the QGauss(2) 
>> points.
>> Can you look into this issue, is the comment in the documentation wrong, 
>> perhaps it should say *do not use QGaussLobatto(2)* ? Or is there some issue 
>> I am missing here ?
> 
> Ah, very interesting question! You're right that in some situations -- the 
> Laplace equation in 1d specifically -- the superconvergence points are in 
> fact the vertices of the cells.
> 
> But that's not true in 2d/3d. There, at least the recollection I have from 
> when I learned about this many years ago, the superconvergence points are 
> indeed the Gauss points. Want to try that out as well in a small experiment? 
> Say take a 16x16 mesh, and plot both solution and discrete solution in a part 
> of the domain well away from the boundary, and see where the two seem to 
> intersect.
> 
> (As always, we're always happy to improve the documentation. Clearly, what I 
> said in step-7 is not the complete truth and ought to be improved, but I'd 
> rather we check what we say before coming up with a better description :-) )
> 
> Cheers
> W.
> 
> -- 
> 
> Wolfgang Bangerth  email: bange...@colostate.edu
>   www: http://www.math.colostate.edu/~bangerth/
> 
> -- 
> The deal.II project is located at http://www.dealii.org/
> For mailing list/forum options, see 
> https://groups.google.com/d/forum/dealii?hl=en
> --- You received this message because you are subscribed to the Google Groups 
> "deal.II User Group" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to dealii+unsubscr...@googlegroups.com.
> To view this discussion on the web visit 
> https://groups.google.com/d/msgid/dealii/d07ed649-dc11-53e4-7e48-3f348f97caf2%40colostate.edu.

-- 
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see 
https://groups.google.com/d/forum/dealii?hl=en
--- 
You received this message because you are subscribed to the Google Groups 
"deal.II User Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/dealii/977AEB90-82E0-4149-99D3-CDEC501B3DCE%40gmail.com.

Re: [deal.II] particle parallelization

[Wolfgang Bangerth]

I have a few questions on the parallelization aspects of a system containing 
particles and I would appreciate it if someone could answer them.
The first one is: Let's say I'm using 2 CPUs for a simulation. If I change a 
property of a ghost particle (located in a ghost cell for CPU0), will the 
property of the real particle on the other CPU change?


Shahab,
the question has already been answered, but I thought I'd also put that into 
the documentation:

  https://github.com/dealii/dealii/pull/10663

Best
 W.
--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/

--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see 
https://groups.google.com/d/forum/dealii?hl=en
--- 
You received this message because you are subscribed to the Google Groups "deal.II User Group" group.

To unsubscribe from this group and stop receiving emails from it, send an email 
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/dealii/788cae53-2cd5-3ba2-84e9-d3eee6310092%40colostate.edu.

Re: [deal.II] step-7 remarks on superconvergence and quadrature

[Wolfgang Bangerth]

In step-7

https://www.dealii.org/current/doxygen/deal.II/step_7.html 



under section on "Verification of correctness”, there is this statement

*(e.g., for linear elements, do not use the QGauss(2) quadrature formula)*

because solution may exhibit superconvergence at the QGauss(2) points.

If we solve

-u’’ = 16*pi^2*sin(4*pi*x) in (0,1)
u(0) = 0, u(1) = 1

using 8 linear elements and QGauss(2) for quadrature.

The error is very small at the vertices of the mesh, not at the QGauss(2) 
points.

Can you look into this issue, is the comment in the documentation wrong, 
perhaps it should say *do not use QGaussLobatto(2)* ? Or is there some issue I 
am missing here ?


Ah, very interesting question! You're right that in some situations -- the 
Laplace equation in 1d specifically -- the superconvergence points are in fact 
the vertices of the cells.


But that's not true in 2d/3d. There, at least the recollection I have from 
when I learned about this many years ago, the superconvergence points are 
indeed the Gauss points. Want to try that out as well in a small experiment? 
Say take a 16x16 mesh, and plot both solution and discrete solution in a part 
of the domain well away from the boundary, and see where the two seem to 
intersect.


(As always, we're always happy to improve the documentation. Clearly, what I 
said in step-7 is not the complete truth and ought to be improved, but I'd 
rather we check what we say before coming up with a better description :-) )


Cheers
 W.

--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/

--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see 
https://groups.google.com/d/forum/dealii?hl=en
--- 
You received this message because you are subscribed to the Google Groups "deal.II User Group" group.

To unsubscribe from this group and stop receiving emails from it, send an email 
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/dealii/d07ed649-dc11-53e4-7e48-3f348f97caf2%40colostate.edu.

Re: [deal.II] Hanging node constraints for one component of a vector system

[Wolfgang Bangerth]

On 7/3/20 11:20 AM, Stephen wrote:
I have an FE system object made of FE_TraceQ and FE_FaceQ and would like to 
apply hanging node (and zero boundary) constraints to only the first 
component. This is easy with zero boundary since the function 
DoFTools::make_zero_boundary_constraints can take a component mask as an 
argument but I see no such variant for 
DofTools::make_hanging_node_constraints; what would be the easiest way to do 
this practically?


Right. That's because make_hanging_node_constraints() in essence just enforces 
a property of the finite element space, namely specific continuity 
constraints. These properties are described by the finite element class.


If I understand you right, then you want an FE_FaceQ that does not require 
continuity from a large face to its child faces -- in other words, you want it 
to be discontinuous. I am curious why you need this? That's because the 
continuity between cells of the same size is implicitly provided. Why do you 
want to treat faces with hanging nodes differently?


(If that's what you really want, you need to come up with a different way to 
describe the finite element space -- using a different class derived from 
FiniteElement -- and I'm happy to walk you through the process. But I 
don't understand why you would want to do that, and so am curious about the 
underlying reason first.)


Best
 W.


--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/

--
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see 
https://groups.google.com/d/forum/dealii?hl=en
--- 
You received this message because you are subscribed to the Google Groups "deal.II User Group" group.

To unsubscribe from this group and stop receiving emails from it, send an email 
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/dealii/dffb5991-4499-33dc-f3b3-747be71652c2%40colostate.edu.

[deal.II] deal.II Newsletter #125

[Rene Gassmoeller]

Hello everyone!

This is deal.II newsletter #125.
It automatically reports recently merged features and discussions about the 
deal.II finite element library.


## Below you find a list of recently proposed or merged features:

#10658: fix warning in bundled taskflow (proposed by tjhei) 
https://github.com/dealii/dealii/pull/10658

#10657: Replace MPI_COMM_WORLD by mpi_communicator in step-50 (proposed by 
dangars; merged) https://github.com/dealii/dealii/pull/10657

#10655: Remove more deprecations (proposed by masterleinad) 
https://github.com/dealii/dealii/pull/10655

#10654: Remove deprecated TransposeTableIterators (proposed by masterleinad) 
https://github.com/dealii/dealii/pull/10654

#10653: Remove unused tests (proposed by dangars) 
https://github.com/dealii/dealii/pull/10653

#10651: Bugfix: Unify dof indices on ghost interfaces if no finite element 
dominates. (proposed by marcfehling) https://github.com/dealii/dealii/pull/10651

#10649: Extend read_vtk to add FIELD data (proposed by OpenFCST) 
https://github.com/dealii/dealii/pull/10649

#10648: Remove LocalIntegrators::grad_div_matrix and 
LocalIntegrators::grad_div_residual (proposed by masterleinad; merged) 
https://github.com/dealii/dealii/pull/10648

#10647: Fix default mapping parameter in VectorTools boundary functions 
(proposed by masterleinad) https://github.com/dealii/dealii/pull/10647

#10646: Add Simplex::FE_P (proposed by peterrum) 
https://github.com/dealii/dealii/pull/10646

#10645: FiniteElementData: select number of objects based on cell type 
(proposed by peterrum) https://github.com/dealii/dealii/pull/10645

#10644: Remve some inlines in tria_accessor.h (proposed by peterrum; merged) 
https://github.com/dealii/dealii/pull/10644

#10643: Add additional quadrature rule for Simplex (proposed by peterrum; 
merged) https://github.com/dealii/dealii/pull/10643

#10642: Add Simplex::ScalarPolynomial (proposed by peterrum) 
https://github.com/dealii/dealii/pull/10642

#10641: Intoduce ReferenceCellInfo (proposed by peterrum) 
https://github.com/dealii/dealii/pull/10641

#10640: examples/step-69: Link in repository for higher-order code (proposed by 
tamiko; merged) https://github.com/dealii/dealii/pull/10640

#10639: Remove GeometryInfro from a few files (proposed by peterrum) 
https://github.com/dealii/dealii/pull/10639

#10637: Introduce ReferenceCell::Type (proposed by peterrum) 
https://github.com/dealii/dealii/pull/10637

#10636: Remove constraint_and_return_value and types_are_equal (proposed by 
masterleinad) https://github.com/dealii/dealii/pull/10636

#10635: Generalize line_orientation() for 2D general meshes (proposed by 
peterrum) https://github.com/dealii/dealii/pull/10635

#10634: Remove deprecated SolverFGMRES::AdditionalData constructor (proposed by 
masterleinad; merged) https://github.com/dealii/dealii/pull/10634

#10633: Fix in log: cpp-taskflow -> taskflow (proposed by peterrum; merged) 
https://github.com/dealii/dealii/pull/10633

#10632: Enable ArrayView for std::array (proposed by peterrum; merged) 
https://github.com/dealii/dealii/pull/10632

#10631: Refactor Triangulation::create_triangulation() (proposed by peterrum) 
https://github.com/dealii/dealii/pull/10631

#10629: Don't suppress error output from FIND_PACKAGE(deal.II ...) in examples 
(proposed by masterleinad; merged) https://github.com/dealii/dealii/pull/10629

#10626: Remove DoFHandlerType from different files (proposed by peterrum; 
merged) https://github.com/dealii/dealii/pull/10626

#10625: Remove deprecated 
parallel::distributed::SolutionTransfer::prepare_serialization() (proposed by 
masterleinad; merged) https://github.com/dealii/dealii/pull/10625

#10624: Suppress TBB deprecation warnings (proposed by masterleinad; merged) 
https://github.com/dealii/dealii/pull/10624

#10611: Archive documentation (proposed by masterleinad; merged) 
https://github.com/dealii/dealii/pull/10611


## And this is a list of recently opened or closed discussions:

#10656: Error using deal.II 9.2.0 on Mac OS Catalina (10.15.5) (opened) 
https://github.com/dealii/dealii/issues/10656

#10652: Deal.II thinks that clang 7.0 is not C++17 compatible (opened and 
closed) https://github.com/dealii/dealii/issues/10652

#10650: Bug: hp DoF unification fails on ghost interfaces if elements do not 
dominate each other (opened) https://github.com/dealii/dealii/issues/10650

#10638: New non-templated version of DoFTools::make_periodicity_constraints 
lead to Trilinos Matrix error code 2 (opened and closed) 
https://github.com/dealii/dealii/issues/10638

#10628: Improve CMAKE error message when deal.II is too old (closed) 
https://github.com/dealii/dealii/issues/10628


A list of all major changes since the last release can be found at 
https://www.dealii.org/developer/doxygen/deal.II/recent_changes.html.


Thanks for being part of the community!


Let us know about questions, problems, bugs or just share your experience by 
writing to dealii@googlegroups.com, or by opening issue

[deal.II] Re: Error while installing dealii

[Bruno Turcksin]

Prakash,

How did you configure deal.II?

Best,

Bruno

On Friday, July 3, 2020 at 5:54:23 AM UTC-4, ME20S001 Bardawal Prakash 
wrote:
>
> Hello,
>I got error while installing dealii, can someone help me for 
> solving this issue?
> Here I'm attaching snapshots of that error message
>
> Thanks & Regards,
> Prakash.
>

-- 
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see 
https://groups.google.com/d/forum/dealii?hl=en
--- 
You received this message because you are subscribed to the Google Groups 
"deal.II User Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/dealii/e70d2377-a0dc-4d31-b047-84f838125239o%40googlegroups.com.

[deal.II] Re: particle parallelization

[Bruno Blais]

Dear Shahab,
No, if you change a property of a particle on proc 0 and this particle is a 
ghost cell on proc 0, this property will not change on proc 1 (which would 
be its owner).
You would need to change the property on proc 1 and then I think the update 
on proc 0 will only be done when you call the exchange_ghost_particles 
function of the ParticleHandler class


On Sunday, 5 July 2020 23:58:16 UTC-4, Shahab Golshan wrote:
>
> Hello,
> I have a few questions on the parallelization aspects of a system 
> containing particles and I would appreciate it if someone could answer them.
> The first one is: Let's say I'm using 2 CPUs for a simulation. If I change 
> a property of a ghost particle (located in a ghost cell for CPU0), will the 
> property of the real particle on the other CPU change?
> Thanks in advance
> Shahab
>

-- 
The deal.II project is located at http://www.dealii.org/
For mailing list/forum options, see 
https://groups.google.com/d/forum/dealii?hl=en
--- 
You received this message because you are subscribed to the Google Groups 
"deal.II User Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to dealii+unsubscr...@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/dealii/ae17f8ab-560a-45b4-9fcc-0a1e5c0a0467o%40googlegroups.com.