(warning: I'm assuming you're using shape functions with nodal degrees of
freedom. Always a dangerous thing to assume!)
Use an ExplicitSystem. Loop over nodes. Use node.dof_number(sys_num,
var_num, 0) to get the dof_number for each variable in both your
LinearImplicitSystem and ExplicitSystem (passing in the right sys_num for
each one). The "0" as the third argument will get the dof index for the
first component for the variable... which if you are using a shape function
with nodal degrees of freedom will be the "value" DoF.
Now use those dof indices to index into the solution vector of your
LinearImplicit system and pull out the values of your primary variables.
Do your calculation and use the dof indices from the ExplicitSystem to
index into the solution vector of the ExplicitSystem to set the output from
your calculations.
Good thing about using a system like this is that the values will
automatically come out in your output file.
Derek
On Mon, Jul 2, 2012 at 7:14 PM, Yusuke Sakamoto
<ysakamoto@...>wrote:
> Is there a good way to explicitly compute the nodal data and save them?
>
> I use LinearImplicitSystem to solve the Stokes equation for velocities
> and pressure. I want to use the computed nodal velocities to explicitly
> compute the displacements at each node using Euler's method or higher
> order method. Also, I want to use the displacements and velocities to
> explicitly compute other physical parameters, such as deformation rate,
> for postprocessing purpose.
>
> Right now, I explicitly compute and save them in NumericVector whose
> length is equal to the number of nodes and put them into the system
> using Syetem::add_vector. If I need the value inside a local element, I
> just interpolate them using shape functions. However, I think there is a
> more efficient way using ExplicitSystem or other classes.
>
> If I am doing something unnecessary, could you tell me a better way to
> do it? Is there any examples?
>
> Thanks,
>
> Yusuke
>
>
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