Hi All,
I have been experimenting with the GW150914 par file (Thanks for putting it together!), which uses Llama multipatch (MP) with McLachlan (ML) and, of course, Carpet AMR in the interior Cartesian patch, tracking the punctures.
I'm noticing three things when looking at Psi4 l2,m2 waveforms (and this is largely independent of extraction radius):
(1) The waveforms have high-frequency wiggles that similar pure-AMR simulations do not show. I don't have a pure AMR simulation for GW150914, but am comparing with an 8-orbit, equal mass, non-spinnning case. I can run GW150914 with pure AMR if need be.
(2) The high-frequency wiggles get *worse* if I decrease the finite differencing order from 8th to 4th order.
(3) This appears to be a wave amplitude-dependent 'feature', since the wiggles are much less pronounced once the waves reach higher amplitudes.
I'm attaching two gnuplot screenshots: fig1.png shows the first ~800 M of Psi4 l2,m2 real at r=136 M with the stock par file and with a modified par file for 4th order. fig2.png is a zoom-in.
I'm also attaching the par file that I'm using for the 4th-order run.
Now my questions: Does anybody have an idea where the high-f noise is coming from and why it's getting worth for lower FD order? Any suggestions on how to mitigate it?
Thanks!
- Christian
