On 09/15/2017 08:32 AM, Yiyang Zhang wrote:
For example, consider the sine-Gordon equation, which is in Step-25.
With the help of the DataPostprocessor class, we can output a plot for
the energy density.
But then, how could we calculate the total energy?
The best scenario would be computing the energy density and total energy
at the same time...
Yiyang -- it's not easily possible to do it both at the same time
(because DataPostprocessor only creates output, but not do any kind of
integration -- so you are missing some information). But it's easy to do
by hand. For example, for the Laplace equation, you would do something
like this (pseudo-code):
double compute_energy ()
{
FEValues fe_values (...);
std::vector<Tensor<1,dim> > solution_gradients (n_q_points);
double energy = 0;
for (cell=...)
{
fe_values.reinit(cell);
fe_values.get_function_gradients (solution,
solution_gradients);
for (q=0...n_q_points)
energy += solution_gradients[q] * solution_gradients[q] *
fe_values.JxW(q);
}
return energy;
}
Best
W.
--
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