On 9/12/21 6:15 PM, Michael Li wrote:
Thank you for your hints. I tried using *shape_value*, but it seems
finite_element_output is a protected member. The error shows as follows:
error*: ‘dealii::internal::FEValuesImplementation::FiniteElementRelatedData<2,
2> dealii::FEValuesBase<2, 2>::finite_element_output’* is protected within
this context
59 | double shape_value =
fe_values.finite_element_output.shape_value(i, q_index);
^~~~~~~~~~~~~~~~~~~~~
*error: ‘class
dealii::internal::FEValuesImplementation::FiniteElementRelatedData<2, 2>’ has
no member named ‘shape_value’; did you mean‘shape_values’?*
Where does the reference to finite_element_output come from? You just need
fe_values.shape_value(i,q_index);
Take a look at any of the tutorial programs -- they all use this syntax, and
they're usually quite a good illustration of how things are typically done
with deal.II :-)
By the way, I also want to get the *shape_grad* of the reference cell to
compare with some other code implementation regarding shape function.
Based on Thong’s method, the following codes gives me the desired results for
a Q1 element:
const FE_Q<2> Q_2d_element(1);
const Point<2> center(1, 1);
That's not the center of the cell :-)
for(unsignedint i=0; i<Q_2d_element.n_dofs_per_cell(); i++)
{
std::cout << " shape value = "<< Q_2d_element.shape_value(i, center);
std::cout << " shape grad = " <<
Q_2d_element.shape_grad(i, center) << std::endl;
}
I wonder if there are other ways to access the shape_grad on the ref cell
directly. Do I need to use *fe_values.inverse_jacobian(q_index) *to convert
from *shape_grad* on the real cell to the reference cell?
If you ask the finite element object, you will get the values, gradients, ...
of the shape functions on the reference cell. If you ask the FEValues object,
you will get the values, gradients, ... of the shape functions on a concrete cell.
Best
W.
--
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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