Thanks for sharing insight!
On Thursday, March 14, 2019 at 12:18:30 PM UTC-5, Wolfgang Bangerth wrote: > > On 3/13/19 8:18 PM, Jaekwang Kim wrote: > > > > > > I wonder now ... > > > > 1. why smaller scale mesh only results such error, > > You have two terms in your matrix, one from the advection term and one > from the reaction term. If you scale the mesh by a factor of c, the > height of the shape functions used in the reaction term does not change, > but the gradient of shape functions used in the advection term is scaled > by 1/c. As a consequence, the balance of the two terms that together > make up the matrix changes and you apparently get into a situation where > the resulting matrix is ill-conditioned or indeed not invertible. > > > > 2. If possible, is there any choice of better preconditionner for my > > system other than SparseILU to go around this problem? > > To make sure that the system you have assembled is correct, I usually > first check with the SparseDirectUMFPACK solver. Once I know that the > system is correct, I think about iterative solvers and preconditioners. > In your case, the system you have is advection dominated, for which it > is notoriously difficult to construct good preconditioners. > > Best > WB > > -- > ------------------------------------------------------------------------ > 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.
