dolfin team mailing list archive

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

Anders Logg wrote:
> On Thu, Nov 26, 2009 at 10:55:14PM +0000, Garth N. Wells wrote:
>>
>> noreply@xxxxxxxxxxxxx wrote:
>>> ------------------------------------------------------------
>>> revno: 4323
>>> committer: Anders Logg <logg@xxxxxxxxx>
>>> branch nick: dolfin-dev
>>> timestamp: Thu 2009-11-26 11:15:01 +0100
>>> message:
>>>   Use Lagrange as default element instead of quadrature for expressions.
>>
>> I thought that we agreed that this is a bad idea.
>>
>> Garth
> 
> I don't see why it is such a bad idea. Either we approximate a
> coefficient by interpolating it into a finite element space or we
> evaluate it at quadrature points. Just two different approaches to
> approximation.
> 

We discussed this a few days ago and agreed that it's not good. How
should the order be chosen? All the finite element codes that I'm aware
of would evaluate an Expression at quadrature points, so that's what
most users would expect.


> Besides, it's the only thing that currently works because of the bug
> in the quadrature code generation that I wasn't able to fix.
> 

That's a different motivation ;).

> The choice of element is controlled by the variable named "Family" in
> the function _auto_select_element_from_shape in expression.py.
> 
> We can make this a global parameter and set the default tor 
> "Quadrature" once it works, 

I'm happy is "Quadrature" is the default, but if it's not the default
will we ever get around to fixing it?

Garth

but it's good to be able to use "Lagrange"
> (or anything else) for testing.
> 
> --
> Anders