dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Saturday 23 January 2010 08:42:14 Garth N. Wells wrote:
> Is it correct that behind the scenes that
> 
>   U0 = Function(V)
>   U  = Function(V)
>   U0.vector()[:] = U.vector()[:]
> 
> involves a GenericVector::get(..) call and a GenericVector::set(..)
> call? If so, it isn't ideal since it introduces unnecessary new/delete
> operations and unnecessary copying of data.

None of GenericVector::get(..) or GenericVector::set(..) are invoked, see 
__getslice__ and __setslice__ in la_post.i.

   U0.vector()[:]

involves 

  GenericVector::operator =(..) 

and 

  U.vector()[:]

involves 

  GenericVector::copy()

However the latter is unnecessary as you instead can do:

  U0.vector()[:] = U.vector()

invoking the assignment operator of U0's vector with U's vector.

Johan