Failed line search are almost always due to an incorrect Jacobian. Please let us know if the suggestions at http://www.mcs.anl.gov/petsc/documentation/faq.html#newton don’t help.
Barry On Mar 14, 2014, at 8:57 PM, Dafang Wang <[email protected]> wrote: > Hi, > > 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? > > 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, > > 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.) > > My simulation input consists of two scalar values (p1 and p2), each of which > acts as a constant pressure boundary condition. > > Case 1, diverge: > p1= -10.190869 p2= -2.367555 > NL step 0, |residual|_2 = 1.621402e-02 > Line search: Using full step: fnorm 1.621401550027e-02 gnorm > 7.022558235262e-05 > NL step 1, |residual|_2 = 7.022558e-05 > Line search: Using full step: fnorm 7.022558235262e-05 gnorm > 1.636418730611e-06 > NL step 2, |residual|_2 = 1.636419e-06 > Nonlinear solve did not converge due to DIVERGED_LINE_SEARCH iterations 2 > Case 2: converge: > p1= -10.190747 p2= -2.367558 > NL step 0, |residual|_2 = 1.621380e-02 > Line search: Using full step: fnorm 1.621379778276e-02 gnorm > 6.976373804153e-05 > NL step 1, |residual|_2 = 6.976374e-05 > Line search: Using full step: fnorm 6.976373804153e-05 gnorm > 4.000992847275e-07 > NL step 2, |residual|_2 = 4.000993e-07 > Line search: Using full step: fnorm 4.000992847275e-07 gnorm > 1.621646014441e-08 > NL step 3, |residual|_2 = 1.621646e-08 > Nonlinear solve converged due to CONVERGED_SNORM_RELATIVE iterations 3 > > 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? > > Any comments will be greatly appreciated. > > Thanks, > Dafang > -- > Dafang Wang, Ph.D > Postdoctoral Fellow > Institute of Computational Medicine > Department of Biomedical Engineering > Johns Hopkins University > Hackerman Hall Room 218 > Baltimore, MD, 21218
