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<div class="moz-cite-prefix">Have you considered using a matrix
shell:<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateShell.html">http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatCreateShell.html</a><br>
<br>
What operations do you need to support besides sparse matrix
vector products?<br>
<br>
On 03/31/2014 10:49 AM, Mathis Friesdorf wrote:<br>
</div>
<blockquote
cite="mid:CALcG_5TuNTzxMKwZoyOWvUt9AD_h82h7ZYr6q7YC72SMSMHKEA@mail.gmail.com"
type="cite">
<div dir="ltr">Hello everybody,<br>
<br>
for my Ph.D. in theoretical quantum mechanics, I am currently
trying to integrate the Schroedinger equation (a linear partial
differential equation). In my field, we are working with so
called local spin chains, which mathematically speaking are
described by tensor products of small vector spaces over several
systems (let's say 20). The matrix corresponding to the
differential equation is called Hamiltonian and can for typical
systems be written as a sum over tensor products where it acts
as the identity on most systems. It normally has the form<br>
<br>
<div style="text-align:left"><i>\sum Id \otimes Id ... Id
\otimes M \otimes Id \otimes ...</i><br>
</div>
<br>
where M takes different positions.I know how to explicitly
construct the full matrix and insert it into Petsc, but for the
interesting applications it is too large to be stored in the
RAM. I would therefore like to implement it as a matrix free
version. <br>
This should be possible using MatCreateMAIJ() and VecGetArray(),
as the following very useful post points out <a
moz-do-not-send="true"
href="http://lists.mcs.anl.gov/pipermail/petsc-users/2011-September/009992.html">http://lists.mcs.anl.gov/pipermail/petsc-users/2011-September/009992.html</a>.
I was wondering whether anybody already made progress with this,
as I am still a bit lost on how to precisely proceed. These
systems really are ubiquitous in theoretical quantum mechanics
and I am sure it would be helpful to quite a lot of people who
still shy away a bit from Petsc.<br>
<br>
Thanks already for your help and all the best, Mathis<br>
</div>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
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