Greetings, I am trying to solve a system of 4 non-linear equations to find 4 unknowns. The equations are slightly complicated and unstable for slightly large values of the unknowns. In most of the cases the correct solution is found. However sometimes the values that are fed to my residual function are big and nan/inf values are produced.
This is the output of my residual function (x are the parameters and f is the computed residual) x= [1, 1, 2, 4]; f= [-1.32993, 6.46116, 0.490443, -4.47854]; x= [2.32993, -5.46116, 1.50956, 8.47854]; f= [-1.77078, -133.872, 4.26217, 71.9728]; x= [1.06488, 0.684771, 1.97607, 4.2185]; f= [-0.431978, 2.79625, 0.190123, 0.0503181]; x= [4.10071, 128.411, -2.75261, -63.4942]; f= [62.0141, 2548.28, -95.0523, -1354.74]; x= [1.74294, 0.960827, 1.63558, 4.54888]; f= [19.6641, 4.52508, -9.48464, 7.44219]; x= [-57.9134, -2419.86, 92.2997, 1291.24]; f= [inf, -inf, inf, -inf]; This was using ngmres, I noticed similar behaviour with other types. What can I do to improve the solver? N ote that my experience with petsc in new and limited. Thank you, -- Abdul Lateef Haji Ali -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130502/ae59cf07/attachment.html>
