I see your point. Since the residue ff[0] and ff[xs+xm-1] are going to be minimized to zero, it forces that xx[0]=0 and xx[xs+xm-1]-1.0=0. So the BC is satisfied.
Thank you. Xiangdong On Wed, Apr 2, 2014 at 3:26 PM, Barry Smith <[email protected]> wrote: > > On Apr 2, 2014, at 1:48 PM, Xiangdong <[email protected]> wrote: > > > > > > > > > On Wed, Apr 2, 2014 at 9:50 AM, Matthew Knepley <[email protected]> > wrote: > > On Wed, Apr 2, 2014 at 8:23 AM, Xiangdong <[email protected]> wrote: > > Hello everyone, > > > > I have two quick questions about src/snes/examples/tutorials/ex3.c. > > > > 1) In line 150-151, why do we need to call MatSeqAIJSetPreallocation > before MatMPIAIJSetPreallocation? I found that without the seqaij call, the > program crashed. However, the mat J we want to create is the mpiaij. > > > > 2) In line 390-397, it sets the values of the residue function at the > boundary. Where do these values come from? In other words, I am not clear > about ff[0]=xx[0] and ff[xs+xm-1] = xx[xs+xm-1] - 1.0; > > At 0 we want to force the solution to be 0. and at 1 we want to force > the solution to be 1. So this is just a way to apply Dirichlet boundary > conditions. > > Barry > > > > > These are just the BC we choose. > > > > The exact solution used in the code is u=x^3. The thing not clear to me > is how this is translated to the boundary conditions I mentioned above. > More like a formulation question, in fact. > > > > Thank you. > > > > Xiangdong > > > > > > Matt > > > > Thank you. > > > > Xiangdong > > > > > > > > -- > > 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 > > > >
