dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

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?

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.

Johan

> Disadvantages are:
>
> - It may be unclear that u0 and u share data.
> - If u goes out of scope, u0 is will keep the vector belonging to u
> alive (only an issue if the vector is very large compared to that
> required by u0).
>
> Garth
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