I have an elliptic PDE of the form Div[n(x) T Grad(phi)]=f(n,...) subject to periodic BC. (phi is the electrostatic potential in a PIC/fluid model). I expect there to be a constant null space but I'm not sure I'm dealing with it properly.
1) Section 4.6 of the manual suggests MatNullSpaceCreate() followed by KSPSetNullSpace(), but I have also seen examples that use MatSetNullSpace(). Is one preferred over the other? 2) Should I follow XXXSetNullSpace() with MatNullSpaceRemove() on the RHS Vec? 3) Do I need to MatNullSpaceDestroy() for either XXXSetNullSpace() option? 4) If so, should the destruction happen after KSPSolve()? 5) The manual (same section) says "You can run with the additional options -pc_factor_shift_nonzero <dampingfactor> or -pc_factor_shift_nonzero <dampingfactor> to prevent a zero pivot." This seems like a typo. I believe I've done my due Google diligence, but I'm happy to be pointed elsewhere if these questions have come up before. --A Different Matt -------------------------------------------------------------- Matthew Young Graduate Student Boston University Dept. of Astronomy --------------------------------------------------------------
