Hi Ankang,

Sorry it has taken rather long to get back to you. Thanks for your clear explanation which I think is very interesting and we should do something about this. Do you have a modified polylib.cpp we can include.

I am not sure if the papers that Dave forwarded offer a more robust way of evaluating the lagging polynomial near the quadrature points since that is the only other modification I can think we might consider.

I am cc’ing Mike so he can also perhaps comments on this point.

Cheers,
Spencer.

> On 14 Apr 2017, at 13:06, Ankang Gao <gaoak@pku.edu.cn> wrote:
>
> Hellow,
>
> I have found two bugs in the codes, and I listed them in the attachment.
>
> I have a question about why the backward differentiation formula starts after m_pressureCalls>2, in function
> void Nektar::Extrapolate::AccelerationBDF(Array< OneD, Array< OneD, NekDouble > > & array).
> Since when m_pressureCalls=2, we can already get a first order accuracy result.
>
>
> thanks
>
> Ankang
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Spencer  Sherwin
McLaren Racing/Royal Academy of Engineering Research Chair,
Professor of Computational Fluid Mechanics,
Department of Aeronautics,
Imperial College London
South Kensington Campus
London SW7 2AZ

s.sherwin@imperial.ac.uk
+44 (0) 20 759 45052