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<big>Hi,<br>
<br>
Does anyone know what the error code DIVERGED_LINE_SEARCH means in
the SNES nonlinear solve? Or what scenario would lead to this
error code?<br>
<br>
Running a solid mechanics simulation, I found that the occurrence
of DIVERGED_LINE_SEARCH was very unpredictable and sensitive to
the input values to my nonlinear system, although my system should
not be that unstable. As shown by the two examples below, my
system diverged in one case and converged in the other, although
the input values in these two cases differed by only 1e-4, <br>
<br>
Moreover, the Newton steps in the two cases were very similar up
to NL step 1. Since then, however, Case 1 encountered a
line-search divergence whereas Case 2 converged successfully. This
is my main confusion. (Note that each residual vector contains
3e04 DOF, so when their L2 norms differ within 1e-4, the two
systems should be very close.)<br>
<br>
My simulation input consists of two scalar values (p1 and p2),
each of which acts as a constant pressure boundary condition. <br>
<br>
Case 1, diverge: <br>
p1= -10.190869 p2= -2.367555 <br>
NL step 0, |residual|_2 = 1.621402e-02<br>
Line search: Using full step: fnorm 1.621401550027e-02 gnorm
7.022558235262e-05<br>
NL step 1, |residual|_2 = 7.022558e-05<br>
Line search: Using full step: fnorm 7.022558235262e-05 gnorm
1.636418730611e-06<br>
NL step 2, |residual|_2 = 1.636419e-06<br>
Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH
iterations 2<br>
</big>
<hr size="2" width="100%"><big>Case 2: converge:<br>
p1= -10.190747 p2= -2.367558 <br>
NL step 0, |residual|_2 = 1.621380e-02<br>
Line search: Using full step: fnorm 1.621379778276e-02 gnorm
6.976373804153e-05<br>
NL step 1, |residual|_2 = 6.976374e-05<br>
Line search: Using full step: fnorm 6.976373804153e-05 gnorm
4.000992847275e-07<br>
NL step 2, |residual|_2 = 4.000993e-07<br>
Line search: Using full step: fnorm 4.000992847275e-07 gnorm
1.621646014441e-08<br>
NL step 3, |residual|_2 = 1.621646e-08<br>
Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE
iterations 3<br>
</big>
<hr size="2" width="100%"><big><br>
Aside from the input values, the initial solution in both cases
may differ very slightly. (Each case is one time step in a
time-sequence simulation. The two cases behaved nearly identically
up to the last time step before the step shown above, so their
initial solutions may differ by a cumulative error but such error
should be very small.) Is it possible that little difference in
initial guess leads to different local minimum regions where the
line search in Case 1 failed?<br>
<br>
Any comments will be greatly appreciated. <br>
<br>
Thanks,<br>
Dafang<br>
</big>
<div class="moz-signature"><big>-- <br>
Dafang Wang, Ph.D <br>
Postdoctoral Fellow <br>
Institute of Computational Medicine <br>
Department of Biomedical Engineering <br>
Johns Hopkins University <br>
Hackerman Hall Room 218 <br>
Baltimore, MD, 21218</big></div>
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