Personal tools
You are here: Home Virgo Data Analysis VDAS vdas_20120419
Log in

Forgot your username or password?
Document Actions


by Marie Anne Bizouard last modified 2012-04-19 17:23


 - Low latency CBC parameter estimation with spins with GPUs at Cascina


MAB, Stefano Cortese, Cristiano Palomba, Salvatore Vitale, Frederique Marion, CVDB, Livio Salconi, Riccardo Sturani, John Veitch, Elena Cuoco, Benoit Mours


John Veitch: several low latency PE developments. Different waveforms + techniques C+python code. No GPU interface. Spin is the issue. Latency of week with spinning waveforms (full spins). MPI MCMC / nested sampling code: not a large gain. Ben Aylott is investigating pyCUDA at Birmingham.

Riccardo: Ben Aylott is gaining a factor 10 wrt non GPU implementation. Key point: code in GPU friendly way, differential equations solver, which is a non parallel code. GPU allows parallelizing. But no spinning waveforms implementation on GPUs so far. Discussions with Leone Bosi about this: thinks this is possible.

John: maybe we could have a kind of hybrid implementation with GPUs for some part of the PE pipeline.

Gergely: what's steps are the time consuming steps. What steps are the bottle neck? template generation?

John: template generation in a nutshell. Filtering is OK. Sequential generation template. You generate one after the other.
Work by Ben Aylott: template in parallel.

Gergely: nb of waveforms to generate?

John 100k <--> 1M

Gergely: generation offline?
John: can't sample the parameter space

Gergerly: pre-calculated template bank?

John: the template bank could be generated. With resolution chosen in advance. Then, need to interpolate between template to have the needed resolution. That's not the present implementation.

Gergely: there would be advantages

John: it does not matter if you have to compute only once.

Gergely: what would be the length of the waveforms

John: size of the template bank is increasing with the low frequency. Millions of template.

Gergely: 1 M of 100s @ 4096 Hz (float)--> 2GB. Could be stored in GPU memory. It would be then possible to pre-calculate the template bank and load it on GPUs. Do filtering on GPUs and interpolate templates on GPU if needed.

Gergely: spinning waveform generation time?
Riccardo: less than a few s.
Gergely: Time of integration?
Riccardo : depends on the sampling rate.
Salvatore: 1kHz is enough for BBH. For BNS we need 4kHz.
Riccardo: integration step depends on the sampling rate.

Other subjects:
John: MBTA is very efficient, but this is still a coincident search. MBTA more coherent? Integration of parameter like inclination angle to get the sky localization.

Benoit: MBTA is coincident. Want to introduce coherence. Add coherence testing using best template in det1  applied in in det2.
Very low level of coherence.

Salvatore: use of MBTA best estimate as priori of PE code?

Frederique: there is a danger of bias, as MBTA estimation can be wrong.

Gergely: MBTA density of template 99% overlap. What is the PE MCMC MM?
John: there is no such MM. Resolution is defined by the code.
John: resolution is fixed by the errors on parameters. Template spacing is not defined a priori.
MAB: no uniform density.
John: yes, what could be done with a fixed template bank is to interpolate between templates. NR projects tried to do that as well.
Frederique: not a simple interpolation, but one needs to take into account.

Gergely: would be happy to learn about MCMC PE code.
John: will send you documentation/papers I wrote with Alberto Vecchio. But implementation on GPUs might be different.
Salvatore: injections 2 spins : ~ 1 week/injection. 50 injections TaylorF2 running: ready 

John: Leone was implementing a code on GPUs. Any news?

Gergely: TaylorF2 waveforms: done by other groups as well. Analytic waveforms. No in
Riccardo: discussions time domain generation of waveforms 6 months ago. But Leone has left Virgo since.

Gergely: the main pb is non analytic waveforms --> integration.

Salvatore: what we want to do, prompt emission EM or afterglow?
Frederique: prompt emission would mean minutes. So afterglow and actually the point is sky localization, to really point in the right direction.

Gergely: who should I contact for more info?
John: For what concerns MCMC/PE : Bayesian maiing. For more general 

MAB: Next steps: Salvatore results before the end of June.

Meeting adjourned