Thanks a lot. That will be a great help. Currently I am doing it calling nek via system function.<div><br></div><div>Best regards</div><div>Praveen<br><br>On Monday, October 27, 2014, <<a href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div>Hi Parveen<br>
<br>
There is implementation of arnoldi time-stepper for spectra
calculation with parpack for nek5000. I think I've already sent
you some info about it. The code you can find at<br>
<a href="ftp://ftp.mech.kth.se/pub/adam/Nek5000/toolbox/" target="_blank">ftp://ftp.mech.kth.se/pub/adam/Nek5000/toolbox/</a><br>
There are sfd and arnoldi set-ups based on ext_cyl example form
repository. The restart of the stepper you can find in the code.
We do it by setting istep to 0 (forces solver to go through
BDF1->BDF2->BDF3->BDF3) and resetting some vectors to
zero.<br>
Best regards<br>
Adam<br>
<br>
On 22/10/14 15:07, <a href="javascript:_e(%7B%7D,'cvml','nek5000-users@lists.mcs.anl.gov');" target="_blank">nek5000-users@lists.mcs.anl.gov</a> wrote:<br>
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<div class="gmail_extra">Hello Paul</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">I dont want to restart in the middle.</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">Every time I want to start the time
stepping from scratch. So I want to know how to reset
everything for a fresh simulation. Every time ARPACK gives me
a vector, I have to start with
BDF1->BDF2->BDF3->BDF3... until final time. </div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">I think accuracy of time stepper also
matters since we are approximating exact evolution operator
exp(A*t) with the time stepper.</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">I have read some papers on time
stepping approach but the details are not clear.</div>
<div class="gmail_extra"><br>
</div>
<div class="gmail_extra">Thanks</div>
<div class="gmail_extra">praveen</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Oct 22, 2014 at 5:06 PM, <span dir="ltr"><<a href="javascript:_e(%7B%7D,'cvml','nek5000-users@lists.mcs.anl.gov');" target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="overflow:hidden">Hi Praveen,<br>
<br>
I would guess you need to develop your own timestepper
because<br>
Nek uses BDFk & EXTk to time march, where typically
k=3. At<br>
start-up, it uses k=1 and k=2 to bootstrap. If you
start timestepping<br>
in the middle of the simulation then you need to
overwrite the<br>
existing coefficients so that you can restart the
timestepper,<br>
plus you need to store your initial condition (which
presumably<br>
amounts to overwriting vx,vy,vz, and pr).<br>
<br>
There are others in the community who have done these
kinds of<br>
things (I have not), who might have some further
comments.<br>
<br>
Best,<br>
<br>
Paul<br>
<br>
PS ----- Are you trying to find eigenvalues associated
with<br>
the spatial operators ? i.e., does the accuracy of the<br>
timestepper matter? If not, you can likely get away
with<br>
k=1, in which case you don't need much history in the
backward<br>
difference formula or extrapolation. Pressure, however,
is<br>
a bit of a tricky business because we use splitting and
there<br>
is a residual O(dt^k) impact...</div>
</blockquote>
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<br>
<br>
</div>
</div>
<br>
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</blockquote>
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