Dear all,
I was going through step-22 and I saw that since you're using primitive
elements, then you compute the local_rhs contribution using
*fe.system_to_component_index(i).first*
However, as written in the program, we could as well multiply the dim+1
tensor having the values of the i-th shape function with the whole rhs
vector (f,0).
So, I have two questions:
1) Are you using *fe.system_to_component_index(i).first *just to make the
program run faster? Why not using extractors?
2) Taking the scalar product between a rank-1 Tensor and a Vector with the
same size is not "conceptually" allowed. Did you have in mind something
like the following?
//inside assemble_system()
std::vector<Tensor<1, dim>> phi_u(dofs_per_cell);
for (unsigned int q = 0; q < n_q_points; ++q)
{
for (unsigned int k = 0; k < dofs_per_cell; ++k)
{
//store symgrad_phi_u, div_phi_u, etc. using extractors
phi_u[k] = fe_values[velocities].value(k, q);
}
// compute local_matrix and local_preconditioner
double sum = 0.0; //store scalar product between first dim components of
i-th shape function (corresponding to velocity) and first dim components of
the rhs
for (unsigned int s = 0; s < dim; ++s)
{
sum += phi_u[i][s] * rhs_values[q][s];
}
local_rhs(i) +=
(sum + rhs_values[q][dim] * phi_p[i]) * fe_values.JxW(q);
}
}
or is there a better way to achieve this?
Best,
Marco
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