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[Nguyen Van Dang <question154697@xxxxxxxxxxxxxxxxxxxxx>]

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
>
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*Nguyen Van Dang

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