GMRES: Convergence

[billy at dem.uminho.pt]

I have specified maximum number of iterations 500 and tolerance 1E-8. Usually it
drives the residual to specified tolerance but in this case GMRES seems to stop
after 15 iterations and the residual is still above tolerance.

  0 KSP Residual norm 2.928143483788e+05
  1 KSP Residual norm 1.403875955158e+05
  2 KSP Residual norm 4.068852804332e+04
  3 KSP Residual norm 8.517044011269e+03
  4 KSP Residual norm 2.179034005404e+03
  5 KSP Residual norm 6.155723927227e+02
  6 KSP Residual norm 1.636241232571e+02
  7 KSP Residual norm 4.839052750735e+01
  8 KSP Residual norm 1.118719384434e+01
  9 KSP Residual norm 3.313977141518e+00
 10 KSP Residual norm 7.447603108045e-01
 11 KSP Residual norm 1.942386237492e-01
 12 KSP Residual norm 4.843647894709e-02
 13 KSP Residual norm 1.215264193249e-02
 14 KSP Residual norm 3.111716140560e-03
 15 KSP Residual norm 7.922640853896e-04

Matrix p Number of iterations: 15 Residual: +7.922641E-04

Anyone knows why this happens?

Billy.