Re: [Getfem-users] High level generic assembly procedures

[Yves Renard]

Dear Marco,

No, "Grad_u.Test_p +p.Grad_Test_u+p.Test_u + p(0)u(0)-p(L)u(L)" is not
valid. The expression of an assembly string is to be evaluated at each
Gauss point of the concerned region. An expression such as "p(0)" will
be understand to be the component 0 of p which is not valid because the
first component is 1.
If you want to add some expression on a boundary (an extremity of the
intervall [0, L] here) then it is possible but not in the same assembly
string. In your example you have to add the assembly string "p.u" at the
boundary x=0 and "-p.u" at the boundary x=L.

However, if you need to prescribe a Dirichlet boundary condition, the
best would be to use a corresponding model brick (if you use the model
system).


Yves.





Le 07/04/2014 15:43, Marco Pischedda a écrit :
> Hi,
>
> how can I impose the boundary condition with high level generic
> assembly? For example I want to assemble "Grad_u.Test_p +
> p.Grad_Test_u+p.Test_u" and then imposing the value of p on the
> boundaries of the 1d domain, i.e x=0 and x=L. It is possible
> to write "Grad_u.Test_p +p.Grad_Test_u+p.Test_u + p(0)u(0)-p(L)u(L)",
> i.e can I insert the boundaries conditions in the assembling string?
>
> Thanks in advance
>
> Marco
>
>
> 2014-04-03 9:52 GMT+02:00 Marco Pischedda <address@hidden>:
>> Dear Yves,
>>
>> thank you for bug correction, now it works.
>>
>>> Concerning your question on Grad_u for a vector field, it is usually an
>>> order two  tensor (a matrix) except in 1D.
>>   Ok that's good.
>>
>> I will let you know if there are other problems.
>>
>> Thank you
>>
>> Marco
>>
>> 2014-04-03 9:25 GMT+02:00 Yves Renard <address@hidden>:
>>>
>>> Dear Marco,
>>>
>>> Concerning your question on Grad_u for a vector field, it is usually an
>>> order two  tensor (a matrix) except in 1D.
>>> I tried to to the best to make the most operations "dimension
>>> indepedent" so there is some permitivity in the langage (components of
>>> size 1 are sometimes ignored).
>>> Remember also that you can have the expression of any term with the
>>> commant Print. For instance "Print( Grad_u).Test_p" will print the
>>> gradient of u on each Gauss point. It does a lot of print, but at least,
>>> you can see the format of the term.
>>>
>>> Yves.
>>>
>>>
>>> Le 02/04/2014 17:21, Marco Pischedda a écrit :
>>>> Hi,
>>>>
>>>> I have other questions:
>>>>
>>>> - I tried to assemble separately the following terms:
>>>>   "Grad_u.Test_p" , "p.Grad_Test_u", "p.Test_u" and the code works 
>>>> correctly.
>>>>   Then I want to assemble the sum of this terms, i.e: "Grad_u.Test_p +
>>>> p.Grad_Test_u+p.Test_u"
>>>>   but I receive the following error:
>>>>
>>>>    Addition or substraction of incompatible expressions or of different 
>>>> sizes
>>>>    terminate called after throwing an instance of 'gmm::gmm_error'
>>>>    what():  Error in getfem_generic_assembly.cc, line 3591 :
>>>>    Error in assembly string
>>>>    Aborted
>>>>
>>>> - I'm working in 1d problem with vectors as unknowns. Grad_u is
>>>> therefore a vector or is a        tensor? When I do Grad_u.Test_p the
>>>> result is a scalar or a vector? Test_p is a vector or a scalar?
>>>>
>>>> Thanks in Advance
>>>>
>>>> Marco
>>>>
>>>>
>>>>
>>>> 2014-04-01 17:51 GMT+02:00 Marco Pischedda <address@hidden>:
>>>>> Ok thank you,
>>>>>
>>>>> I tried it and it works. I will let you know if there are other problems.
>>>>>
>>>>> Thanks
>>>>>
>>>>> Marco
>>>>>
>>>>> 2014-04-01 17:16 GMT+02:00 Yves Renard <address@hidden>:
>>>>>> Dear Marco,
>>>>>>
>>>>>> All seems to me correct in your implementation. This is probably just
>>>>>> the test line 2074 of getfem_generic_assembly.cc
>>>>>> which is not correct for one-dimensionnal problems.
>>>>>>
>>>>>> I think the test should be
>>>>>>
>>>>>>  GA_DEBUG_ASSERT((qdim == 1 && t.sizes()[0] == N) ||
>>>>>>                       (t.sizes()[1] == N && t.sizes()[0] == qdim) ||
>>>>>>                       (N == 1 && t.sizes()[0] == qdim),
>>>>>>                       "dimensions mismatch");
>>>>>>
>>>>>> May be you can try this. I will validate it if it works.
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Yves.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Le 01/04/2014 16:56, Marco Pischedda a écrit :
>>>>>>> Dear Yves,
>>>>>>>
>>>>>>> thank you for your fast answer.
>>>>>>>
>>>>>>> I have another question:
>>>>>>>
>>>>>>> - I have a monodimensional problem but the unknowns are vectorial. I
>>>>>>> set the vectorial
>>>>>>> dimension of the unknows with mf_u.set_qdim(3) and with 
>>>>>>> mf_p.set_qdim(3).
>>>>>>> When I define the expression " Grad_u.Test_p "  i receive the following 
>>>>>>> error:
>>>>>>>
>>>>>>> terminate called after throwing an instance of 'gmm::gmm_error'
>>>>>>>   what():  Error in
>>>>>>> ../../getfem-svn/getfem/src/getfem_generic_assembly.cc, line 2074 :
>>>>>>> dimensions mismatch
>>>>>>>
>>>>>>> Grad_u should be a 2nd order tensor, while Test_p should be a vector.
>>>>>>> I suppose the
>>>>>>> problem is that Grad_u is interpreted as a vector while Test_p is
>>>>>>> interpreted as a scalar.
>>>>>>> How can I use the high level generic assembly procedures on vectorial 
>>>>>>> problems
>>>>>>> defined on a monodimensional computational domain?
>>>>>>>
>>>>>>> Thanks in advance
>>>>>>>
>>>>>>> Marco
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> 2014-04-01 8:42 GMT+02:00 Yves Renard <address@hidden>:
>>>>>>>> Dear Marco,
>>>>>>>>
>>>>>>>> Yes, your code is correct and it should work correctly.
>>>>>>>> Note that you can also use the high level generic assembly with the
>>>>>>>> model object using a generic assembly brick.
>>>>>>>> Note also that high level assembly is only available in the svn
>>>>>>>> repository version of Getfem
>>>>>>>> (and a very recent version, at least r4570 because a bug have been
>>>>>>>> corrected on coupled problems recently).
>>>>>>>>
>>>>>>>> Yves.
>>>>>>>>
>>>>>>>>
>>>>>>>> Le 31/03/2014 14:00, Marco Pischedda a écrit :
>>>>>>>>> Dear all,
>>>>>>>>>
>>>>>>>>> I want to use the high level generic assembly procedures in order to
>>>>>>>>> use the automatic differentation for calculating the Jacobian of a
>>>>>>>>> non-linear problem.
>>>>>>>>>
>>>>>>>>> For example I want to calculate the Jacobian of two vectorial
>>>>>>>>> equations in the unknowns "u" and "p". The first vectorial equation is
>>>>>>>>> (u+p).Test_u while the second is (u+p).Test_p.
>>>>>>>>>
>>>>>>>>>  It is correct the following code?
>>>>>>>>>
>>>>>>>>>  gmm::sub_interval Iu(0, ndofs_u);
>>>>>>>>>  gmm::sub_interval Ip(ndofs_u,ndofs_p);
>>>>>>>>>  workspace.add_fem_variable("u", mf_u, Iu, U);
>>>>>>>>>  workspace.add_fem_variable("p", mf_p, Ip, P);
>>>>>>>>>  workspace.add_expression("(u+p).Test_u + (u+p).Test_p",mim);
>>>>>>>>>  getfem::model_real_sparse_matrix Jac(ndofs_u+ndofs_p, 
>>>>>>>>> ndofs_u+ndofs_p);
>>>>>>>>>  workspace.set_assembled_matrix(Jac);
>>>>>>>>>  workspace.assembly(2);
>>>>>>>>>
>>>>>>>>> In the matrix Jac I have the Jacobian of the system?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Thanks in advance
>>>>>>>>>
>>>>>>>>> Marco
>>>>>>>>>
>>>>>>>>> _______________________________________________
>>>>>>>>> Getfem-users mailing list
>>>>>>>>> address@hidden
>>>>>>>>> https://mail.gna.org/listinfo/getfem-users
>>>>>>>> --
>>>>>>>>
>>>>>>>>   Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
>>>>>>>>   Pole de Mathematiques, INSA-Lyon             fax : (33) 
>>>>>>>> 04.72.43.85.29
>>>>>>>>   20, rue Albert Einstein
>>>>>>>>   69621 Villeurbanne Cedex, FRANCE
>>>>>>>>   http://math.univ-lyon1.fr/~renard
>>>>>>>>
>>>>>>>> ---------
>>>>>>>>
>>>>>> --
>>>>>>
>>>>>>   Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
>>>>>>   Pole de Mathematiques, INSA-Lyon             fax : (33) 04.72.43.85.29
>>>>>>   20, rue Albert Einstein
>>>>>>   69621 Villeurbanne Cedex, FRANCE
>>>>>>   http://math.univ-lyon1.fr/~renard
>>>>>>
>>>>>> ---------
>>>>>>
>>>
>>> --
>>>
>>>   Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
>>>   Pole de Mathematiques, INSA-Lyon             fax : (33) 04.72.43.85.29
>>>   20, rue Albert Einstein
>>>   69621 Villeurbanne Cedex, FRANCE
>>>   http://math.univ-lyon1.fr/~renard
>>>
>>> ---------
>>>


-- 

  Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
  Pole de Mathematiques, INSA-Lyon             fax : (33) 04.72.43.85.29
  20, rue Albert Einstein
  69621 Villeurbanne Cedex, FRANCE
  http://math.univ-lyon1.fr/~renard

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