[Dune] Help for gradient calculation

[Christian Engwer]

On Thu, Jul 14, 2011 at 02:21:04PM +0530, DHIRENDRA VAIDYA wrote:
> I am trying to calculate electric field from -grad(potential). potential is
> obtained from solving poisson's equation by finite element method and node
> values are stored in block vector. possion's equation is solved simillar to
> grid-howto tutorial. now i am stuck in calculating potential gradient with
> these node values of potential. i tried calculating gradient of
> shapefunction at nodes and then multiply it with potential node value, but
> gradient of shapefunction is coming out to be zero at nodes(might be bcoz at
> node gradient is undefined). so how to calculate gradient?

actually you are not asking how to compute the gradient in dune, but
how to obtain the gradient of a Q1-function. If you look into your
favorite FEM-textbook, you can read this in detail. Short answer
is... compute the gradient contributions element-wise and sum up the
contributions from each element.

Cheers
Christian

> On Mon, Jul 11, 2011 at 5:32 PM, Jö Fahlke <jorrit at jorrit.de> wrote:
> 
> > Am Mon, 11. Jul 2011, 10:53:38 +0200 schrieb Oliver Sander:
> > > Please be more specific when writing questions.
> >
> > To make the request to be more specific more specific: what kind of
> > function
> > are you talking about?  For instance, is it a discrete function, and if so,
> > what discretization module are you using?
> >
> > Bye,
> > Jö.
> >
> > --
> > Computers are like air conditioners.  Both stop working, if you open
> > windows.
> > -- Adam Heath
> >
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> 
> 
> -- 
> Warm Regards,
> Dhirendra Vaidya

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