Dear Wolfgang, In attach you shall find the bilinear form and the assemble part of the code as well.
Thanks, On Friday, October 21, 2016 at 11:14:52 AM UTC-5, Wolfgang Bangerth wrote: > > > > On Thursday, October 20, 2016 at 9:48:55 PM UTC-5, Wolfgang Bangerth > wrote: > > > > What is the norm of the first right hand side? You now set the > tolerance in > > > > the first iteration to a fixed value of 1e-16, but how does this > compare to > > the previous value of 1e-12*system_rhs.l2_norm()? > > > > > > The system_rhs.l2_norm() before the first call to CGSolverat in the zero > time > > step was 1.82492e-09, so that the 1e-12*system_rhs.l2_norm() became in > the > > order of 1e-21 by which CGSOlver didn't converge. > > OK. I have no suggestion, though, why one or the other would lead to > convergence or non-convergence of CG. > > > > That still seems wrong to me. As I mentioned in a previous email, > you > > ought to > > make sure that the matrix you build is the matrix you *want* to > build. > > > > > > I was wondering how to make sure the matrix I built is what I meant. > > You need to compare properties of your bilinear form with those of your > matrix. For example, if your bilinear form is symmetric, then your matrix > is > as well -- and that is something you can test. If your bilinear form is > positive definite, then your matrix needs to be as well and as a > consequence > CG needs to converge. If CG does not seem to converge but your bilinear > form > is s.p.d., you know you have a bug in your matrix assembly. If CG > converges on > one processor but not on two for the same problem, then you know you have > a > bug in the parallel matrix assembly. Etc. > > Since you haven't stated your bilinear form or the problem you are > solving, I > can't tell you whether the matrix is supposed to be s.p.d. > > Best > W. > > > -- > ------------------------------------------------------------------------ > Wolfgang Bangerth email: bang...@colostate.edu > <javascript:> > www: http://www.math.colostate.edu/~bangerth/ > > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Bilinearform.docx
Description: MS-Word 2007 document
