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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Matt:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> petsc-dev-bounces@mcs.anl.gov [mailto:petsc-dev-bounces@mcs.anl.gov] <b>On Behalf Of </b>Matthew Knepley<br><b>Sent:</b> Wednesday, December 14, 2011 5:15 PM<br><b>To:</b> For users of the development version of PETSc<br><b>Subject:</b> Re: [petsc-dev] controlling vector values while doing matrix free operations<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>On Wed, Dec 14, 2011 at 4:07 PM, Philip, Bobby <<a href="mailto:philipb@ornl.gov">philipb@ornl.gov</a>> wrote:<o:p></o:p></p><div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><p class=MsoNormal>Hi:<br><br>When doing the following operation in PETSc using FD approximations to a Jacobian vector product<br><br>J'(u)*a = [J(u+h*a) - J(u)]/h<o:p></o:p></p></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Usually, we would put in F where you have J.<o:p></o:p></p></div><div><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Actually this is taken from PETSc documentation so you may want to modify it. I normally do use F also.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><p class=MsoNormal>is there a way for the user to specify that the entries of u+h*a cannot be negative for example?<br>Browsing the PETSc documentation it was not obvious whether I could do this.<o:p></o:p></p></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>You can do whatever you want in your F function, but you should really investigate SNESVI if<o:p></o:p></p></div><div><p class=MsoNormal>you have bounds on your variables.<o:p></o:p></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I do indeed control F and u but I do not control h*a. This is determined by PETSc. Hence the possibility<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>exists that u+h*a is outside the domain of the function. This is what I would like to control. Being able to<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>check whether u+h*a lies in the domain of the function and then potentially modifying it so it does much <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>in the flavor of the LineSearchPost and PreCheck functions. Any suggestions?<o:p></o:p></span></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> Thanks,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal> Matt<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><p class=MsoNormal>Thanks,<br>Bobby<o:p></o:p></p></blockquote></div><p class=MsoNormal><br><br clear=all><o:p></o:p></p><div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>-- Norbert Wiener<o:p></o:p></p></div></body></html>