[petsc-users] Simple KSP with known solution gives infinite solution

[Smith, Barry F.]

  Run with -ksp_converged_reason



> On May 23, 2018, at 12:10 PM, zakaryah <zakaryah at gmail.com> wrote:
> 
> I'm looking for some help with a terribly simple problem.  I am trying to solve a linear system which is very small, as a test.  The vectors are derived from a minimal 3D DMDA (3x3x3), with 3 dof, so that the RHS and solution vectors have dimension 81 and the matrix is 81x81.  I have checked that the matrix is symmetric, invertible (empty null space), and that the desired solution is reasonable, i.e. has no large values.  The condition number of the matrix is about 3600.  When I run KSPSolve with default settings, I see convergence in a single iteration (gmres, pc_type lu, jacobi, none, or svd).  However, the solution is infinite in all entries.  Any suggestions for debugging this?  Thanks!