Dear Daniel,
I am sorry It is a typo error, actually, I have old_s =
old_solution_values[q_point](1) which represents the solution at previous
time step i.e. U(t_{n-1}) and old_s0 =
old_solution_values0 [q_point](1) which represents the solution at time
(t_{n-2}) i.e. U(t_{n-2}) and old_s1 = old_solution_values1 [q_point](1) which
represents the
solution at time (t_{n-3}) i.e. U(t_{n-3}). The old_solution_values and
old_solution_values1 are different as I explained above. I need these
values of the solutions (second component of the solution) at previous time
steps to assemble the right hand side nonlinear term in y problem.
Best
Mohammad
On Tuesday, June 7, 2016 at 10:29:45 AM UTC+1, Mohammad Sabawi wrote:
>
> Dear all,
>
>
>
> I am solving a 3x3 block system arising form DG time discretisation of the
> semilinear parabolic equations in the form u_t - \Delta u = f(u) for the
> block solution vector U which consists from three nodal values blocks U0,
> U1 and U2. During the solution process I need just the solution values of
> the second block U1 at the previous time steps (t_{n-1}, t_{n-2} and
> t_{n-3})
>
> i.e. old_solution.block(1), old_old_solution.block(1) and
> old_old_old_solution.block(1) for this task I used
>
>
>
> std::vector<Vector<double> old_solution_values (n_q_points,
> Vector<double>(3));
>
> std::vector<Vector<double> old_solution_values0 (n_q_points,
> Vector<double>(3));
>
> std::vector<Vector<double> old_solution_values1 (n_q_points,
> Vector<double>(3));
>
>
>
> fe_values.get_function_values (old_solution, old_solution_values);
>
> fe_values.get_function_values (old_old_solution, old_solution_values0);
>
> fe_values.get_function_values (old_old_old_solution, old_solution_values1);
>
>
>
>
>
> In the solution process in the right hand side assembly I need just the
> nodal values of second block U1 at the previous time steps (t_{n-1},
> t_{n-2} and t_{n-3}) i.e. old_solution.block(1)
>
>
>
> For this reason, I used
>
>
>
> const double old_s = old_solution_values[q_point](1);
>
> const double old_s = old_solution_values0[q_point](1);
>
> const double old_s = old_solution_values1[q_point](1);
>
>
>
>
>
> but I did not get required results and even when I changed
> old_solution_values[q_point](1) to old_solution_values[q_point](0) nothing
> has changed (just to check if there is any difference) and even when I
> tried the wrong thing old_solution.block(1) nothing has changed and I got
> the same results as with previous other cases.
>
>
>
> I am confused about this case; did I do some thing wrong in defining the
> nodal values of the second block of the solution vector at the previous
> time steps? Any feedbacks and hints are appreciated.
>
>
>
> Best regards
>
>
>
> Mohammad Sabawi
>
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