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Jed and others,<br>
<br>
we would like to explore more in detail the possibility to have a
completely matrix-free preconditioner.<br>
May you explain which are the "few methods" that we should implement
and that you was talking of ?<br>
<br>
Second question: are there algorithms for creating matrix-free
preconditioners ?<br>
If yes, may you suggest at least one, please ?<br>
<br>
Thank you in advance.<br>
Best regards,<br>
<br>
Michele<br>
<br>
Jed Brown wrote:
<blockquote
cite="mid:CAM9tzS=SCV1_NhkaxMd=okgF4UsqvTR7QyDsGu7oygqcz5rdCQ@mail.gmail.com"
type="cite">
<div class="gmail_quote">On Mon, Sep 12, 2011 at 16:28, Michele De
Stefano <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:mstefano@milan.westerngeco.slb.com">mstefano@milan.westerngeco.slb.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote"
style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div id=":8l">KSPSetOperators is able to accept a shell matrix for
the "Amat" and the manual<br>
says that the "Pmat" is usually the same as the "Amat". Does this
really work<br>
also when "Amat" is a shell matrix ?<br>
<br>
I mean, in the multi-process case, the default preconditioning method
is block<br>
Jacobi ... but does this work also when "Pmat" is a shell matrix ?</div>
</blockquote>
</div>
<br>
<div>Only if a few methods are implemented for the shell matrix. This
is usually not practical. It would be more common to assemble some
approximation Pmat (e.g. in AIJ format) and use that for
preconditioning. To do everything matrix-free, you would normally have
to put some effort into writing your own custom preconditioner.</div>
</blockquote>
<br>
<div class="moz-signature">-- <br>
Michele De Stefano
<br>
Senior Geophysicist - REMS
<br>
Integrated EM Center of Excellence
<br>
<br>
WesternGeco GeoSolutions,
<br>
Via Clericetti 42/A,
<br>
20133, Milan - Italy
<br>
<br>
+39 02 266279232 (direct)
<br>
+39 02 266279279 (fax)
<br>
<br>
<a href="mailto:mstefano@slb.com">mstefano@slb.com</a>
<br>
<br>
Schlumberger Private
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