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<div class="">On Feb 4, 2017, at 7:47 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div>
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<div class="gmail_quote">On Sat, Feb 4, 2017 at 7:44 PM, Jed Brown <span dir="ltr" class="">
<<a href="mailto:jed@jedbrown.org" target="_blank" class="">jed@jedbrown.org</a>></span> wrote:<br class="">
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Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> writes:<br class="">
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> On Sat, Feb 4, 2017 at 7:24 PM, Zhang, Hong <<a href="mailto:hongzhang@anl.gov" class="">hongzhang@anl.gov</a>> wrote:<br class="">
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>> Can you elaborate a bit more on your problem?<br class="">
>><br class="">
>> If your problem is an index-1 DAE, there is no need to use a projection<br class="">
>> method, and it is perfectly fine to set it up as a DAE in PETSc. For<br class="">
>> high-index DAEs, you may have to use TSSetPostStep() to implement your own<br class="">
>> projection algorithm.<br class="">
>><br class="">
><br class="">
> Please define index.<br class="">
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Think of it as a measure of singularity of the "mass matrix". Higher<br class="">
index DAE have more complicated constraints on compatibility of initial<br class="">
conditions. It's covered in any book or paper on DAEs.<br class="">
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Both your explanation and Hong's use of the term do not help Gideon (or me) know whether he has an index-1 DAE. There has</div>
<div class="gmail_extra">to be some simple form you can write down so that we can tell.</div>
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<div>This is why we need to learn more about Gideon's problem. It is easy to determine the index if he can write down his problem in a simple form. But it is not that easy the other way round.</div>
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<div>Hong </div>
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<div class="gmail_extra"> Matt<br clear="all" class="">
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<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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