dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxx>]

Anders Logg wrote:
> On Mon, Apr 23, 2007 at 11:31:40PM +0200, Garth N. Wells wrote:
>
> > Anders Logg wrote:
> > > On Mon, Apr 23, 2007 at 06:50:17PM +0200, Garth N. Wells wrote:
> > > > Quoting Anders Logg <logg@xxxxxxxxx>:
> > > >
> > > > > On Mon, Apr 23, 2007 at 07:04:16PM +0200, DOLFIN wrote:
> > > > > > One or more new changesets pushed to the primary DOLFIN repository.
> > > > > > A short summary of the last three changesets is included below.
> > > > > >
> > > > > > changeset:   2900:cc8dbffbcc9cebe6761eceb5b91d324e0ec2caf0
> > > > > > tag:         tip
> > > > > > user:        "Garth N. Wells <g.n.wells@xxxxxxxxxx>"
> > > > > > date:        Mon Apr 23 19:04:03 2007 +0200
> > > > > > files:       src/kernel/io/VTKFile.cpp
> > > > > > description:
> > > > > > Fix VTK outout. Results look ok now.
> > > > > Very nice. Maybe we should put back the same boundary condition as we
> > > > > had before and compare the results (the solution vector number by
> > > > > number) with the old demo. That would be a very good indicator that
> > > > > we are on the right track.
> > > > Do we still need to do some work on applying Dirichlet boundary conditions to
> > > > particular components of a vector only, or is this already implemented?
> > > >
> > > > Garth
> > > I think this is not needed for the elasticity demo since we set the
> > > values for all the vector components. The displacement is u = [0, 0, 0]
> > > at one end and u = [ux, uy, uz] at the other end.
> > Looks like the boundary condition at one end is u = [-, uy, uz].
>
> ok, I see that now. It's sort of a strange boundary condition. You
> twist the gear around the x-axis but allow it to slide in the
> x-direction.
>
> > I've applied the same boundary conditions for the new and the old
> > code, 
>
> Setting ux to 0 in both?

I set ux = 1 in the second.

> > and the results are close, but not the same. One issue is that FFC is 
> > producing code with fewer significant digits than previously.
>
> How close?

With the displacement fixed at one end only and a unit body force in all 
directions,

 ( ||u^old||_2 - ||u^new||_2 ) / ||u^old||_2 = 0.001

and with no body force, just applied displacements (RHS vectors are 
identical),

 ( ||u^old||_2 - ||u^new||_2 ) / ||u^old||_2 = 0.0003.

These numbers look small, but they hide that the results do jump around 
a bit.

> Kristian and I reduced the number of significant digits to get
> reproducible results when running the regression test in FFC. (The
> last digits may otherwise differ between different machines, Python
> versions, time of day, weather conditions etc.)

Can I easily increase the number just for testing?

Garth

> /Anders
>
>
> > Garth
> >
> > > This problem does not show up until we get to the Stokes demo.
> > >
> > > /Anders
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