ufl team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On Nov 9 2009, Harish Narayanan wrote:

> Anders Logg wrote:
> > On Mon, Nov 09, 2009 at 02:05:29PM +0100, Anders Logg wrote:
> > > On Mon, Nov 09, 2009 at 12:58:32PM +0000, Garth N. Wells wrote:
> > > > Marie Rognes wrote:
> > > > > Kristian Oelgaard wrote:
> > > > > > Quoting Anders Logg <logg@xxxxxxxxx>:
> > > > > >
> > > > > >
> > > > > > > This is something we've discussed before, but I want to discuss it
> > > > > > > again.
> > > > > > >
> > > > > > > Could we change the definition of the gradient of a vector to be the
> > > > > > > "normal" definition:
> > > > > > >
> > > > > > >   grad(u) = du_i / dx_j
> > > > > > >
> > > > > > > ?
> > > > > > I think this sounds like an excellent idea.
> > > > > Me too.
> > > > Cowards! ;) You wait for Martin the leave and then jump on the 
> > > > bandwagon.
> > > >
> > > > I suggested this March/April, and Martin's argument against was for
> > > > consistency with other operations. I think that it's fine to change so
> > > > long that other operations do not break or lead to
> > > > unexpected/inconsistent results.
> > > :-)
> > >
> > > I've had this discussion with Martin at least twice and both times he
> > > managed to convince me of his definition. But I keep forgetting the
> > > arguments in favor of the current definition (and more so when it
> > > gets me into trouble).
> >
> > I've created a blueprint:
> >
> > https://blueprints.launchpad.net/ufl/+spec/redine-grad
> >
> > Add your comments there. (Harish, add comments on div.)
>
> I will. And there might be something similar with curl too, but who uses
> curl anyway! :)
>
> I'd just like to point out that in future discussion, I think it will be
> clearer if you used the following notation grad(u)_ij = du_i / dx_j.

Yes, otherwise we could have 

 grad(u)_ji = du_i / dx_j 

which would keep Martin happy :).

Garth

> Harish
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