<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="">Would setting it up as a DAE in petsc be algorithmically euivalent to a projected method (i.e., step of standard RK followed by nonlinear projection)?<div class=""><br class=""><div class="">
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">-gideon</span>
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<br class=""><div><blockquote type="cite" class=""><div class="">On Feb 3, 2017, at 11:47 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">That is one answer. Another one is that this particular system is a DAE and we have methods for that.<div class=""><br class=""></div><div class=""> Matt</div></div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Fri, Feb 3, 2017 at 8:40 PM, Barry Smith <span dir="ltr" class=""><<a href="mailto:bsmith@mcs.anl.gov" target="_blank" class="">bsmith@mcs.anl.gov</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br class="">
TSSetPostStep(); in your function use TSGetSolution() to get the current solution.<br class="">
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Please let us know how it works out<br class="">
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Barry<br class="">
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> On Feb 3, 2017, at 7:14 PM, Gideon Simpson <<a href="mailto:gideon.simpson@gmail.com" class="">gideon.simpson@gmail.com</a>> wrote:<br class="">
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> I’m interested in implementing a projection method for an ODE of the form:<br class="">
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> y’ = f(y),<br class="">
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> such that g(y) = 0 for all time (i.e., g is conserved). Note that in a projection method, a standard time step is made to produce y* from y_{n}, and then this is corrected to obtain y_{n+1} satisfying g(y) = 0.<br class="">
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> There were two ways I was thinking of doing this, and I was hoping to get some input:<br class="">
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> Idea 1: Manually loop through using taking a time step and then implementing the projection routine. I see that there is a TSStep command, but this doesn’t seem to be much documentation on how to use it in this scenario. Does anyone have any guidance?<br class="">
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> Idea 2: Is there some analog to TSMonitor that allows me to modify the solution after each time step, instead of just allowing for some computation of a statistic?<br class="">
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</div></div></blockquote></div><br class=""><br clear="all" class=""><div class=""><br class=""></div>-- <br class=""><div class="gmail_signature" data-smartmail="gmail_signature">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br class="">-- Norbert Wiener</div>
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