dolfin team mailing list archive

[Johan Hake <question154697@xxxxxxxxxxxxxxxxxxxxx>]

Question #154697 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/154697

    Status: Open => Answered

Johan Hake proposed the following answer:
Not sure what you mean.

You call evaluate_basis_derivatives with a value argument. Without knowing too 
much how the generated code is supposed to be used, I would suspect that you 
would then need to pass a pointer to a C-array with appropriate length to get 
the correct values out.

Johan

On Monday May 2 2011 09:27:21 Nguyen Van Dang wrote:
> Question #154697 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/154697
> 
>     Status: Answered => Open
> 
> Nguyen Van Dang is still having a problem:
> It works. Thank you very much for your help.
> However, the form of basis functions is phi(x,y). So, my expectation is
> getting the gradient of these functions. It means that the output is a
> vector, not a scalar. Would you like to tell me how to do that?
> Thanks in advance,
> 
> Nguyen Van Dang
> 
> On Sun, May 1, 2011 at 10:27 PM, Johan Hake <
> 
> question154697@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > Your question #154697 on DOLFIN changed:
> > https://answers.launchpad.net/dolfin/+question/154697
> > 
> >    Status: Open => Answered
> > 
> > Johan Hake proposed the following answer:
> > dolfin::FiniteElemens is a thin wrapper around ufc::finite_element and
> > are ment for the dolfin library to access. Therefore are most of the
> > function only
> > available using ufc cell. However, some of the methods have been made
> > available using a dolfin::cell. These are evaluate_basis and
> > evaluate_basis_all. The last one only in the development version of
> > dolfin.
> > 
> > Garth or Anders need to comment on if we want to dublicate more of these
> > functions or if we should force the user to construct a UFCCell to call
> > the methos with. If I am not totally of the latter should be possible
> > by:
> > 
> > ...
> > #include <"dolfin/fem/UFCCell.h">
> > ...
> > dolfin::UFCCell ufc_cell(c);
> > finite_element.evaluate_basis_derivatives(i,n,dvalues,coordinates,ufc_cel
> > l)
> > 
> > 
> > Johan
> > 
> > On Sunday May 1 2011 02:45:30 Nguyen Van Dang wrote:
> > > Question #154697 on DOLFIN changed:
> > > https://answers.launchpad.net/dolfin/+question/154697
> > > 
> > >     Status: Answered => Open
> > > 
> > > Nguyen Van Dang is still having a problem:
> > > Thank you very much for your reply.
> > > However, I still got problem with evaluate_basis_derivatives. My code
> > > is
> > 
> > as
> > 
> > > follows:
> > >   Poisson::FunctionSpace V(mesh);
> > >   const dolfin::FiniteElement& finite_element = V.element();
> > >   const dolfin::Cell& c = Cell(mesh,0);
> > >   unsigned int i = 0;
> > >   unsigned int n = 1;
> > >   double values[1] = {0.0};
> > >   double coordinates[2] = {0.0,0.5};
> > >   //finite_element.evaluate_basis(i,values,coordinates,c)  ;
> > >   //std::cout<<"basis_value ="<<*values<< std::endl;
> > >   double dval[2] = {0.0,0.0};
> > >   double* dvalues = &dval[0];
> > >   unsigned int n = 1;
> > >   finite_element.evaluate_basis_derivatives(i,n,dvalues,coordinates,c)
> > >   ;
> > > 
> > > I got error because of the fourth variable c. In my program c is
> > > declared as dofin::Cell& but in original function its type is
> > > ufc::cell&. My questions are:
> > > 1. Why didn't I get this problem for evaluate_basis?
> > > 2. What will I do to fix this problem for evaluate_basis_derivatives?
> > > 
> > > Please help me again.
> > > Thanks in advance.
> > > Nguyen Van Dang
> > > 
> > > On Fri, Apr 29, 2011 at 3:24 PM, Anders Logg <
> > > 
> > > question154697@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > > > Your question #154697 on DOLFIN changed:
> > > > https://answers.launchpad.net/dolfin/+question/154697
> > > > 
> > > >     Status: Open => Answered
> > > > 
> > > > Anders Logg proposed the following answer:
> > > > 
> > > > On Fri, Apr 29, 2011 at 08:01:55AM -0000, Nguyen Van Dang wrote:
> > > > > New question #154697 on DOLFIN:
> > > > > https://answers.launchpad.net/dolfin/+question/154697
> > > > > 
> > > > > Hello,
> > > > > 
> > > > > I am working with FEnics on C++. I want to take the values of basis
> > > > 
> > > > function at each vertex directly. I read BasisFunction.h online but I
> > > > don't know how to use this one.
> > > > 
> > > > > Finally, I found in "Poisson.h" (created from "Poisson.ufl" in
> > > > 
> > > > dolfin/demo/pde/poisson/cpp) class "poisson_finite_element_0" in
> > > > which there is function "evaluate_basis(unsigned int i, double*
> > > > values, double* coordinates, const ufc::cell& c)".
> > > > 
> > > > > In "main.cpp" (in the same directory), I wrote:
> > > > >    unsigned int i;
> > > > >    double* values;
> > > > >    double* coordinates;
> > > > >    ufc::cell c;
> > > > >    poisson_finite_element_0 finite_element;
> > > > >    finite_element.evaluate_basis(i,values,coordinates,c);
> > > > > 
> > > > > I compiled it without any errors.
> > > > > The problem is that how to input the value for c?
> > > > > In fact, I have read the paper "efficient representation of
> > > > > computational
> > > > 
> > > > meshes" of A. Logg and I could make a loop for all cells as well as
> > > > vertices. However, the cell in this loop doesn't match with c anymore
> > > > (because they have different type). Moreover, it is difficult to
> > > > initialize
> > > > 
> > > > the cell data structure:
> > > > >   c.entity_indices = new unsigned int [...];
> > > > >   c.coordinates = new double[..];
> > > > >   .....
> > > > > 
> > > > > Is there any simple way to do this? Do you have any examples
> > > > > working
> > 
> > on
> > 
> > > > basis functions?
> > > > 
> > > > Look at the FiniteElement class and the function
> > > > interpolate_vertex_values.
> > > > 
> > > > More generally (for evaluation at arbitrary points), you can use the
> > > > functions evaluate_basis or evaluate_basis_all.
> > > > 
> > > > --
> > > > Anders
> > > > 
> > > > --
> > > > If this answers your question, please go to the following page to let
> > 
> > us
> > 
> > > > know that it is solved:
> > https://answers.launchpad.net/dolfin/+question/154697/+confirm?answer_id=
> > 
> > > > 0
> > > > 
> > > > If you still need help, you can reply to this email or go to the
> > > > following page to enter your feedback:
> > > > https://answers.launchpad.net/dolfin/+question/154697
> > > > 
> > > > You received this question notification because you are a direct
> > > > subscriber of the question.
> > 
> > --
> > If this answers your question, please go to the following page to let us
> > know that it is solved:
> > https://answers.launchpad.net/dolfin/+question/154697/+confirm?answer_id=
> > 2
> > 
> > If you still need help, you can reply to this email or go to the
> > following page to enter your feedback:
> > https://answers.launchpad.net/dolfin/+question/154697
> > 
> > You received this question notification because you are a direct
> > subscriber of the question.

-- 
You received this question notification because you are a member of
DOLFIN Team, which is an answer contact for DOLFIN.