[petsc-users] KSPBuildSolution

[Hung Thanh Nguyen]

Hi Pets use
I just install Pets on Windows (I am using C compiler and ITL MKL). And, then running ex2.cpp .... to get error :

Error   2        error: identifier "_intel_fast_memcpy" is undefined    C:\cygwin\home\Hung\petsc-3.1-
p7\include\petscsys.h   1775

Please help me. Best regard Hung T. Nguyen

-----Original Message-----
From: petsc-users-bounces at mcs.anl.gov [mailto:petsc-users-bounces at mcs.anl.gov] On Behalf Of Juha Jäykkä
Sent: 21. februar 2011 13:10
To: petsc-users at mcs.anl.gov
Subject: Re: [petsc-users] KSPBuildSolution

> > introduce new variables to reduce the problem to a first order equation.
> > For example let g = f'  and the new problem is F(f,g,g') = 0 with
> > the additional equations g = f' now there are no second derivatives.
> Let me see what happens if I do that...

Ok, so this helps. Now I can get the solution to converge on a small lattice, of less than 20 points.

Increasing the lattice gives divergent zig-zag "solutions". Now this is usual central differences behaviour: it decouples even lattice points from odd ones and now that I have both f and f' as unknowns, this decoupling is total. (It was not previously, since f'', computed from f, does not decouple.)

Changing to simple forward differences does not help, but changing to three- point forward differences (=five-point stencil, but the backwards points are not used) fixes the problem and I now get convergence.

That is, thanks for all the help. I can now return to my actual equation, which still does not converge with these tricks on any lattice larger than about 50 points. I suppose the problem here is similar and I just need to find a better discretisation.

Cheers,
Juha

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                | Juha Jäykkä, juhaj at iki.fi                     |
                | http://www.maths.leeds.ac.uk/~juhaj           |
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