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 >
