On Feb 19, 2013, at 12:53 PM, Marcelo Xavier Guterres <m.guterres at gmail.com> wrote:
> Esteemed colleague, > > thanks for the previous answer. But still can not understand one aspect. > > > The GMRES behaves well up to a point, but then the quality of the final > solution is bad, compared to analytical solution. > > > It is a problem in the method or truncation error? No, it is an approximate solver and it gets worse as the problem size increases. CG gets worse also. CG is just better for this problem. > > > m n m x n error ( KSPCG x PCJACOBI ) error ( KSPGMRS x > PCJACOBI ) > 3 3 9 1,92E?16 4,42E?16 > > 4 4 16 2,08E?16 6,46E?16 > > 5 5 25 4,41E?16 9,63E?16 > > 6 6 36 8,77E?16 8,26E?16 > > 7 7 49 2,37E?06 2,52E?06 > > 8 8 64 1,17E?05 1,33E?05 > > 9 9 81 9,32E?06 1,26E?05 > > 10 10 100 7,33E?06 9,93E?06 > > 20 20 400 4,22E?05 3,16E?04 > > 30 30 900 1,06E?04 2,37E?02 > > 40 40 1600 2,14E?04 3,77E?02 > > 50 50 2500 3,37E?04 9,36E?03 > > 100 100 10000 1,27E?03 6,53E?02 > > 200 200 40000 4,32E?03 3,67E?01 > > 300 300 90000 9,53E?02 1,02E+00 > > 400 400 160000 1,68E?02 2,10E+00 > > 500 500 250000 2,61E?02 3,66E+00 > > > > > -- > Sauda??es Pampeanas > -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- > > Phd. student Marcelo -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130219/1d0c5ea5/attachment.html>
