Please ignore my message. I implemented the fix for grad(phi_i) within my
code but that still does not solve my problem.

Best
praveen

On Wed, Oct 5, 2016 at 10:42 AM, Praveen C <cprav...@gmail.com> wrote:

> Dear all
>
> While a solving a conservation law with DG, I find that total mass is not
> conserved. To get total mass conservation, we need
>
> sum_(i=0,1,...ndofs-1) grad(phi_i(xq, yq, zq)) = 0
>
> where phi_i are shape functions and
>
> ndofs = fe.dofs_per_cell
>
> and above equation must hold at every quadrature point (xq,yq,zq).
>
> I have checked in my application that above sum is O(1e-14). While this is
> small, it seems to lead to slow mass loss as it gets multiplied by a large
> number.
>
> This can be easily fixed by taking
>
> grad(phi_0(xq, yq, zq)) = - sum_(i=1,...ndofs-1) grad(phi_i(xq, yq, zq))
>
> I want to test if this really solves my conservation problem.
>
> Can you help me by pointing out in which function I have to put this fix ?
> Somewhere in FEValues class ?
>
> Thanks
> praveen
>
>
>

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