On Sunday 24 January 2010 16:12:37 Garth N. Wells wrote: > Johan Hake wrote: > > On Sunday 24 January 2010 00:03:41 Garth N. Wells wrote: > >> Johan Hake wrote: > >>> On Saturday 23 January 2010 14:55:08 Garth N. Wells wrote: > >>>> Johan Hake wrote: > >>>>> 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. > >>>> > >>>> What happens if I do > >>>> > >>>> x = U.vector()[:] > >>> > >>> It just triggers the copy method of GenericVector, which is the same > >>> behavior as for other itterable Python types. > >>> > >>>> ? Is x a numpy array? > >>> > >>> No you need to call array() to accomplish that. > >> > >> OK. What I'm trying to do is > >> > >> # Get vectors > >> u_vec = u.vector()[:] > >> u0_vec = u0.vector()[:] > >> v0_vec = v0.vector()[:] > >> a0_vec = a0.vector()[:] > > > > You should not need to make a copy of the vectors here. > > How can I avoid it?
a_vec and v_vec are new vectors. None of the four vectors below get modified by the a_vec and v_vec expressions so no need of copying, and the v0 and a0 assignment should work with GenericVectors too. Do you get any error messages? Johan > What I have now (which is working) is > > # Get vectors (copies of) > u_vec = u.vector().array() > u0_vec = u0.vector().array() > v0_vec = v0.vector().array() > a0_vec = a0.vector().array() > > # Update acceleration and velocity > a_vec = (1.0/(2.0*beta))*( (u_vec - u0_vec - v0_vec*dt)/(0.5*dt*dt)\ > - (1.0-2.0*beta)*a0_vec ) > v_vec = dt*((1.0-gamma)*a0_vec + gamma*a_vec) + v0_vec > Garth > > >> a_vec = 1.0/(2.0*beta)*((u_vec-u0_vec - v0_vec*dt)/(0.5*dt*dt) \ > >> - (1.0-2.0*beta)*a0_vec) > >> v_vec = dt*((1.0-gamma)*a0_vec + gamma*a_vec) + v0_vec > > > > The expression cause a lot of intermediate vectors, but should work, if > > beta, gamma and dt are all scalars. > > > >> # Update (U0 <- U0) > >> v0.vector()[:] = v_vec > >> a0.vector()[:] = a_vec > > > > This should work. > > > > Johan > > > >> I guess I need to call array() to make this work? > >> > >> Garth > >> > >>> Johan > >>> > >>>> Garth > >>>> > >>>>> Johan > _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : [email protected] Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
