On 10/6/2012 2:42 PM, Matthew Knepley wrote: > On Sun, Jun 10, 2012 at 5:42 PM, TAY wee-beng <zonexo at gmail.com > <mailto:zonexo at gmail.com>> wrote: > > Hi, > > Currently, my matrix A changes its non zero position at each time > step. > > For e.g.: At a particular node, at time step = 1, I will insert > values into its east, west neighbours. At time step = 2, I will > insert values into its east, north neighbours. Hence, the non-zero > positions at each row will be different at each time step. > However, the max values per row will always be 5 or less. > > Currently, after MatSetValues and MatAssemblyBegin/End, I call: > > /call MatSetOption(A_mat,MAT_NEW_NONZERO_LOCATIONS,PETSC_TRUE,ierr) > > call KSPSetOperators(ksp,A_mat,A_mat,DIFFERENT_NONZERO_PATTERN,ierr) > > call KSPGetPC(ksp,pc,ierr) > > ksptype=KSPBCGS > > call KSPSetType(ksp,ksptype,ierr) > > call KSPSetFromOptions(ksp,ierr) > > call KSPSolve(ksp,b_rhs,xx,ierr)/ > > Is this sufficient and correct? If so, apart from KSPSolve, > MatSetValues and MatAssemblyBegin/End, can I only call the other > subroutines once at the 1st time step? > > Or do I have to explicitly destroy the matrix and create a new > one? I think I ask this question a while ago but I can't find the > email now. > > > After assembly the nonzero pattern is fixed. The right thing to do is > put in explicit zeros for the rest of the stencil. > > Matt Hi,
Just to clarify, do you mean that I create a bigger stencil and put in explicit zeros for those which I don't need at each time step? I realise that for my problem, instead of the original 5 non-zero locations (east, west, north, south, center) for the stencil, I now have 4 more (east-east, west-west etc). So now I call MATCREATEAIJ with dnz + o_nz = 9 (instead of previously 5). Is that correct? > > > -- > Yours sincerely, > > TAY wee-beng > > > > > -- > 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120610/2e05dddf/attachment.html>
