Marco,
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?
I think it is an oversight. I would accept a patch to correct that :-)
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);
}
}
That would work. I think a better solution would be to say outright that only
the first equation can have force terms, and then make the RightHandSide class
derived from TensorFunction<1,dim> and let it return its values as
Tensor<1,dim> objects for which you can take the dot product
fe_values[u].shape_value(q) * rhs_values[q]
Want to give this a try and write a patch? We'd be happy to walk you through
what is necessary for such a patch!
Best
Wolfgang
--
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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