[petsc-users] why we have a zero residual?

[Fande Kong]

Hi all,

I was wondering why we will get a zero residual when solving the linear
step of a nonlinear problem? I am solving a fluid-structure interaction
problems using inexact Newton method, within which fGMRES is used together
with a multilevel Schwarz preconditioner. The algorithm works well when the
mesh is small, but it catched a zero residual issue when we turn to use a
little bit large mesh.  The output is listed as follows:

0 SNES Function norm 1.291775443677e-02
  Jacobian: rows 5575441  Column 5575441
call DMGetInterpolation_SpmcsDMMesh
  Jacobian: rows 1298448  Column 1298448
    0 KSP Residual norm 1.291775443677e-02
    1 KSP Residual norm 0.000000000000e+00
Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH iterations 0


Any suggestions? Thanks.

Fande,
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