On Aug 17, 2009, at 8:39 AM, Kent Andre wrote:
On ma., 2009-08-17 at 13:14 +0100, Garth N. Wells wrote:
Johan Hake wrote:
On Monday 17 August 2009 14:03:55 Garth N. Wells wrote:
Johan Hake wrote:
On Monday 17 August 2009 13:33:21 Garth N. Wells wrote:
Please send any comments on how a SubFunction should work as I'm
going
to work on it soon (the Cahn-Hilliard demo runs in parallel(!) ;)
with
the exception of the extraction of sub-Functions for output). I'm
inlined to change a sub function such that for
Function u0 = u[0]
the Function u0 will only point the vector belonging to u rather than
creating a new vector. The advantages are:
- No need to copy a vector
- DofMap will not require 'is_view'
- Possible to do things like
u0 = 0.0;
u1 += v;
u0.interpolate();
What would Function::vector() for a SubFunction then return? The
original
full Vector?
Yes.
Ok.
It would be cool to add a view of the original Vector that only
represents the values of the dofs in the SubFunction, without coping
data. I fiddled around with this when adding slicing for the
PyDOLFIN la
interface, but realized that it would be too difficult.
This is more or less what I plan to do, although internally. A user
wouldn't see the vector, but operations like interpolate would only
involve part of the vector.
I see. Other direct Vector operations would then operate directly on
the
shared Vector, like get, set, aso.
We could add a class like
VectorView(GenericVector& x, DofMap& dof),
which could derive from GenericVector, to provide views. It isn't a
priority for me though.
Yes, I also thought along these lines, however I did not think of
doing it
using a DofMap, which really is the natural thing. I will also not have
possibility to priorities it for now.
On second thought,
VectorView(GenericVector& x, std::vector<uint> map& map)
would be better. The DofMap could produce the map,
std::vector<uint> map = dofmap.view();
Garth
This would be great! This is sort of the reason why I implemented block
matrices in the first place, but this is far more general and there
is no need to mess with the block structure during assembly.
Hi All,
just adding my me-too this suggestion (the Index Set (IS) in PETSc,
provides similar functionality which is very useful)
In particular, I find that the new version of SubFunction a bit
misleading when it returns the entire vector rather than the sub vector
corresponding to just the subfunction.
(I'm whining because it's breaking some of my previous code, but that's
less important).
Consider the following from a Stokes problem
Function w; //full velocity-pressure solution
Function u = w[0];
Function p = w[1];
Function ux = u[0];
Function uy = u[1];
if you plot or write to a file u,p,ux, or uy you get what you expect
just the portion of the solution that is the subfunction,
but if you request something like
ux.vector().max()
you'll get the unexpected result of the maximum of the entire vector i.e.
ux.vector().max() == uy.vector().max() == p.vector().max()
which in this case will be the maximum pressure. This really threw me
(particularly since I was trying to calculate the maximum vector
magnitude and getting very strange solutions)
