<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""></div> It looks like both converged in your image, just at different rates? Note the two sides used different number of linear iterations, my guess is some default behavior of the linear solvers changed between those two ancient releases. First make sure both are using identical linear solvers. Then run both with -pc_type lu do they now have the same SNES convergence?<div class=""><br class=""></div><div class=""> Barry</div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Dec 29, 2020, at 2:51 AM, 朱昭霓 <<a href="mailto:zhuzhaoni2017@hnu.edu.cn" class="">zhuzhaoni2017@hnu.edu.cn</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class=""><font class=""><p class="MsoNormal"><span class="src"><span lang="EN-US" class="">Dear Sir or Madam:</span></span> </p><p class="MsoNormal"><span class="src"><span lang="EN-US" class="">Hello, I am a new PETSc
learner. There are some confusions when I using different versions of PETSc. For
some reasons, I have to change my codes from the version 3.6.3 to 3.4.5. Newton
methods in 3.6.3 version converged successfully with the time step size dt=100.
While with the same dt=100 and almost the same codes, Newton methods in version
3.4.5 failed to converge. The debug test indicated that there may be something
wrong during the line search process. I have tried to search the changes in
different versions but failed. Could you please give me some suggestions? Thank
you so much.</span></span> </p><p class="MsoNormal">Best regards,</p><p class="MsoNormal">Zhaoni Zhu</p></font></div><div class=""><includetail class=""><!--<![endif]--></includetail></div><span id="cid:79511EBA-74DD-4F6D-B4FA-18843E6D98B2"><Error_report.jpg></span></div></blockquote></div><br class=""></div></body></html>