[petsc-users] KSPBuildSolution
Matthew Knepley
knepley at gmail.com
Mon Feb 21 09:36:16 CST 2011
Send all the output of 'make test' along with configure.log and make.log to
petsc-maint at mcs.anl.gov
Matt
On Mon, Feb 21, 2011 at 9:12 AM, Hung Thanh Nguyen <
hung.thanh.nguyen at petrell.no> wrote:
> 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
>
> --
> -----------------------------------------------
> | Juha Jäykkä, juhaj at iki.fi |
> | http://www.maths.leeds.ac.uk/~juhaj |
> -----------------------------------------------
>
--
What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
lead.
-- Norbert Wiener
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