<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">The coming back to the original problem, I’m still unsure of how to diagnose the problem. <div class=""><br class=""></div><div class="">I am not sure if the listserv supports image attachments, but I dumped the snes_check_jacobian_view to disk and inspected the matrices with the spy command. I find that no entry in the saved matrix has absolute value larger than 10^{-2}. There are some that have absolute value larger than 10^{-3}, but the actual values of the entries at those indices are on the order of 100 or 1000, meaning that they are small in a relative sense.<div class=""><br class=""><div class="">
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<br class=""><div><blockquote type="cite" class=""><div class="">On Sep 9, 2015, at 12:19 PM, Jed Brown <<a href="mailto:jed@jedbrown.org" class="">jed@jedbrown.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">Gideon Simpson <<a href="mailto:gideon.simpson@gmail.com" class="">gideon.simpson@gmail.com</a>> writes:<br class=""><br class=""><blockquote type="cite" class="">Checking the Jacobian, this is a pretty standard output:<br class=""><br class=""> Testing hand-coded Jacobian, if the ratio is O(1.e-8), the hand-coded Jacobian is probably correct.<br class=""> Finite difference Jacobian<br class=""> Hand-coded Jacobian<br class=""> Hand-coded minus finite difference Jacobian<br class=""> 6.08281e-10 = ||J - Jfd||//J|| 0.000151055 = ||J - Jfd||<br class=""><br class=""><br class="">Things look favorable in terms of relative difference, but the absolute difference is a bit more suspect.<br class=""></blockquote><br class="">It likely just means you have big matrix entries (perhaps due to poor nondimensionalization/scaling).<br class=""></div></blockquote></div><br class=""></div></div></body></html>