Salman Habib - Los Alamos National Laboratory
Salman Habib - Los Alamos National Laboratory
Salman Habib - Los Alamos National Laboratory
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Mass Resolution: Technical Issues Matter!<br />
• How many particles needed? Test<br />
with different particle loading in 1Gpc<br />
box<br />
‣ Run 1024³ particles as reference<br />
‣ Downsample to 512³ and 256³ particles<br />
and run forward<br />
‣ In addition: downsample z=0,1 1024³<br />
results to characterize shot noise<br />
problem<br />
• For precision answers, interparticle<br />
spacing has to be small! Previous<br />
hand-waving arguments and folk<br />
theorems incorrect<br />
• Requirement: k < k_Ny/2 (no surprise<br />
to Shannon)<br />
• Gigaparsec box requires billion<br />
particle minimum, thus a factor of 10<br />
increase in resolution will require a<br />
trillion particles!<br />
• Force resolution is not the limiting<br />
factor, but mass resolution is<br />
256³ particles k_Ny/2<br />
512³ particles<br />
Katrin Heitmann, <strong>Los</strong> <strong>Alamos</strong> <strong>National</strong> <strong>Laboratory</strong> LBNL, March 12, 2009<br />
z=1<br />
z=0<br />
Downsampled<br />
to 512³<br />
Downsampled<br />
to 256³
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