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[Anders Logg <question154697@xxxxxxxxxxxxxxxxxxxxx>]

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

Anders Logg proposed the following answer:
Just look it up in the UFC manual.

--
Anders


On Mon, May 02, 2011 at 09:40:24AM -0700, Johan Hake wrote:
> 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.
> > > > >
> > >
> > > 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.
> > >
>
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