Judy,
(1) I reset <dim = 1> thru step-8 and step-3. Was that sufficient to
make the program ready for 1-dimensional(1D) PDE?
If not sufficient, I might get more coordinate returned for each
quadrature point; for example, q_index = {0, 1} can be 2D coordinate for
each quadrature point, that caused error?
I don't understand what q_index={0,1} means? q_index is just a single
number, the number of the quadrature point.
(2) Regarding to "obtain quadrature point coordinate locally", my .cc
file for 1D PDE with pure Dirichlet BCs is attached ready to compile for
testing, which was made with reference to step-8 that looped quadrature
points inside each cell locally:
void::assemble_system(){
...
for (const unsigned int q_index : fe_values.quadrature_point_indices())
{
std::cout << fe.degree << std::endl; //added line to output;
std::cout << q_index << std::endl; //added line to output;
std::cout << fe_values.quadrature_point << std::endl; //added line to
output;
I don't believe that this last line actually compiles.
fe_values.quadrature_point is a function, it needs an argument in
(parentheses), probably q_index.
The added lines returned data for each cell, like:
(cell 0:)
2
0
0.00211325
0.005
2
1
0.00788675
0.005
OK, 0.0021... and 0.0078... are the quadrature points on the first cell.
I assume that the cell has size 0.01. The two values are then the Gauss
points on this cell, in the global coordinate system. (On the reference
cell in 1d, that is [0,1], they would have coordinates 0.211325 and
0.788675.)
The returned data from fe_values.quadrature_point {0.00211325,
0.00788675, 0.0121132, 0.0178860, ...}, look like quadrature points in
physical coordinate, moving along 1D domain of (0, 0.1) with looping
cells. However, I did not figure out more information on them.
Yes, this is correct. What more would you want to know about them?
When I switch to Q2 element, fe.degree became 2, but
fe_values.JxW(q_index) does not return expected weights of {1./6.,
2./3., 1./6.}. Was that due to Jacobians of Q2 element? I must be wrong
in guessing and obtaining quadrature point coordinate either locally or
globally, as well as their quadrature weights.
The weights of quadrature points are determined by the quadrature object
you choose, not the finite element object you choose. Have you changed
the quadrature object to QGauss(3) when you changed the finite element
to FE_Q(2)?
Best
W.
--
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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