On 12/12/22 05:41, Abbas wrote:
I am solving a vector problem similar to step-8. I have
aVector<double> solution with u_x and u_y at each dof. I would like to have
another Vector<double> magnitude which stores the magnitude \sqrt(u_x^2+u_y^2)
at each dof. Now it is clear that solution has double the size of magnitude. I
need to extract the values of the magnitude vector for my weak form within the
assembly loop not for post-processing.
Why do I need this? Well I don't actually want the magnitude exactly, but what
I need is the maximum value of my magnitude when I iterate in time.
That sounds very much like you want to solve a nonlinear system -- for which
step-15 shows you how to access this sort of information.
The point to note regarding step-15, though, is that it never actually creates
a vector that stores what in your case is the magnitude. That's because the
magnitude you show above is not actually a finite element field even though
u_x and u_y are: Even though the latter are bilinear functions (assuming you
are using a Q1 element), the magnitude is not a binlinear function. As a
consequence, you don't want to compute it at each node and then interpolate it
at quadrature points; rather, you want to compute it at each quadrature point
from the original solutions u_x and u_y.
Best
W.
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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