For example, if I solve flow problem with Taylor hood element as step-22
tutorial program, and take the first derivatives of the acquired solution
velocity using Datapostprocessor Class,
I could easily get my target quantities (derivatives) for all same dof points.
However, I come up with the fact that my finite elements is only
C0-continuous...at the vertex where two different elements meet.
Correct. That means that there are multiple values of the gradient at
vertices, and indeed we put multiple values into the output file.
(My taylor element is degree 2 for velocity and degree 1 for pressure. )
If then, on those vertexes, how the Datapostprocessor decides which element to
refer for the first, or second derivatives on that dof?
It doesn't use locations of DoFs but the vertices of cells. And it outputs the
same vertex as many times as there are adjacent cells, if necessary with
different values. This is the same as if you had, for example, a piecewise
constant field -- every cell is shown in graphical output as a horizontal
plane, and at vertices several of these planes come together.
Best
W.
--
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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