Question #92245 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/92245
Status: Open => Answered
Patrick Riesen proposed the following answer:
hey phil,
you can extract or set some subfunction values with something like
*snip*
// extract velocity solution and scale it
dolfin::uint m_e = _e->vector().size();
dolfin::uint m = _v->vector().size();
double* _block = new double[m];
dolfin::uint* _rows = new dolfin::uint[m];
for(dolfin::uint i = 0; i < m; i++)
_rows[i] = m_e + i;
_evp->vector().get(_block, m, _rows);
*snap*
in the above code, evp is a function with three subfunctions (e,v,p).
i need to fetch the values from v (thats evp[1]) and do something with
them. they are located in evp with an offset m_e (that's the length of
e, i.e. evp[0]).
get() will return them in _block, then do something with this and use
set(_block, m, _rows) to put the values back in.
( note that this is dolfin0.9.4, (changeset7400) )
Since the programmers refernce is off the site, I can't
> look there.
you can generate the programmers reference yourself if you call the
script makedoc (~/dolfin/scripts)
(you need doxygen installed and you'll find the reference in
~/dolfin/doc/progr_ref.. )
> The second part of my question involves FunctionSapces. The only thing I am
> using GradAvg for is defining Neumann BCs. As I understand it, I need to
> define the same number of points for my Function as there are in the domain
> that was used to create the FunctionSpace. For example, if "mesh" has 100
> nodes, if I need to define 100 values, regardless of if the subdomain I am
> using this Function in only has 8 nodes. All the values that I don't care
> about should be set to zero, or i guess it doesn't really matter, since they
> won't be used. At least, that's the way I've been doing when the numbering
> system doesn't match up with my boundary. Because when nodes 0 through 7 will
> be assigned the first 8 values, and if those nodes aren't on your boundary,
> they won't be used.
> But since it's now possible to define a Function without including a
> FunctionSpace, how will dolfin figure it out?
i think that's not possible anymore. Function() will not work. you need
to specify the FunctionSpace. Or else you use Expression.
I have a subdomain for my neumann BC. Do I just need to define values
for every point in my subdomain?
I guess here you want to use the Expression class to specify your BC
values. from the demos you can learn how to use the Expression class.
patrick
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