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[Nguyen Van Dang <question154697@xxxxxxxxxxxxxxxxxxxxx>]

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?

Please help me!
Thanks in advance

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