47 research outputs found
A Gradient-Interleaved Scheduler for Energy-Efficient Backpropagation for Training Neural Networks
This paper addresses design of accelerators using systolic architectures for
training of neural networks using a novel gradient interleaving approach.
Training the neural network involves backpropagation of error and computation
of gradients with respect to the activation functions and weights. It is shown
that the gradient with respect to the activation function can be computed using
a weight-stationary systolic array while the gradient with respect to the
weights can be computed using an output-stationary systolic array. The novelty
of the proposed approach lies in interleaving the computations of these two
gradients to the same configurable systolic array. This results in reuse of the
variables from one computation to the other and eliminates unnecessary memory
accesses. The proposed approach leads to 1.4 - 2.2 times savings in terms of
number of cycles and savings in terms of memory accesses. Thus,
the proposed accelerator reduces latency and energy consumption.Comment: Proc. 2020 IEEE International Symposium on Circuits and Systems
(ISCAS
SCV-GNN: Sparse Compressed Vector-based Graph Neural Network Aggregation
Graph neural networks (GNNs) have emerged as a powerful tool to process
graph-based data in fields like communication networks, molecular interactions,
chemistry, social networks, and neuroscience. GNNs are characterized by the
ultra-sparse nature of their adjacency matrix that necessitates the development
of dedicated hardware beyond general-purpose sparse matrix multipliers. While
there has been extensive research on designing dedicated hardware accelerators
for GNNs, few have extensively explored the impact of the sparse storage format
on the efficiency of the GNN accelerators. This paper proposes SCV-GNN with the
novel sparse compressed vectors (SCV) format optimized for the aggregation
operation. We use Z-Morton ordering to derive a data-locality-based computation
ordering and partitioning scheme. The paper also presents how the proposed
SCV-GNN is scalable on a vector processing system. Experimental results over
various datasets show that the proposed method achieves a geometric mean
speedup of and over CSC and CSR aggregation
operations, respectively. The proposed method also reduces the memory traffic
by a factor of and over compressed sparse column
(CSC) and compressed sparse row (CSR), respectively. Thus, the proposed novel
aggregation format reduces the latency and memory access for GNN inference
Improved upper limits on the stochastic gravitational-wave background from 2009-2010 LIGO and Virgo data
Paper producido por "The LIGO Scientific Collaboration and the Virgo Collaboration". (En el registro se mencionan solo algunos autores de las decenas de personas que participan).Gravitational waves from a variety of sources are predicted to superpose to create a stochastic
background. This background is expected to contain unique information from throughout the history of
the Universe that is unavailable through standard electromagnetic observations, making its study of
fundamental importance to understanding the evolution of the Universe. We carry out a search for the
stochastic background with the latest data from the LIGO and Virgo detectors. Consistent with predictions from most stochastic gravitational-wave background models, the data display no evidence of a stochastic gravitational-wave signal. Assuming a gravitational-wave spectrum of ΩGWĂ°fĂ ÂŒ Ωαðf=frefĂα, we place 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.5â1726 Hz. In the frequency band of 41.5â169.25 Hz for a spectral index of αŒ 0, we constrain the energy density of the stochastic background to be ΩGWĂ°fĂ <5.6 Ă 10â6. For the 600â1000 Hz band, ΩGWĂ°fĂ <0.14Ă°f=900 HzĂ3, a factor of 2.5 lower than the best previously reported upper limits. We find ΩGWĂ°fĂ <1.8 Ă 10â4 using a spectral index of zero for 170â600 Hz and ΩGWĂ°fĂ < 1.0Ă°f=1300 HzĂ3 for 1000â1726 Hz, bands in which no previous direct limits have been placed. The limits in these four bands are the lowest direct measurements to date on the stochastic background. We discuss the implications of these results in light of the recent claim by the BICEP2 experiment of the possible evidence for inflationary gravitational waves.http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.231101publishedVersionFil: Aasi, J. LIGO. California Institute of Technology; Estados Unidos de AmĂ©rica.Fil: Maglione, C. Universidad Nacional de CĂłrdoba. Facultad de MatemĂĄtica, AstronomĂa y FĂsica; Argentina.Fil: Maglione, C. Argentinian Gravitational Wave Group; Argentina.Fil: Quiroga, G. Universidad Nacional de CĂłrdoba. Facultad de MatemĂĄtica, AstronomĂa y FĂsica; Argentina.Fil: Quiroga, G. Argentinian Gravitational Wave Group; Argentina.FĂsica de PartĂculas y Campo
First searches for optical counterparts to gravitational-wave candidate events
During the Laser Interferometer Gravitational-wave Observatory and Virgo joint science runs in 2009-2010, gravitational wave (GW) data from three interferometer detectors were analyzed within minutes to select GW candidate events and infer their apparent sky positions. Target coordinates were transmitted to several telescopes for follow-up observations aimed at the detection of an associated optical transient. Images were obtained for eight such GW candidates. We present the methods used to analyze the image data as well as the transient search results. No optical transient was identified with a convincing association with any of these candidates, and none of the GW triggers showed strong evidence for being astrophysical in nature. We compare the sensitivities of these observations to several model light curves from possible sources of interest, and discuss prospects for future joint GW-optical observations of this type
First all-sky search for continuous gravitational waves from unknown sources in binary systems
We present the first results of an all-sky search for continuous
gravitational waves from unknown spinning neutron stars in binary systems using
LIGO and Virgo data. Using a specially developed analysis program, the TwoSpect
algorithm, the search was carried out on data from the sixth LIGO Science Run
and the second and third Virgo Science Runs. The search covers a range of
frequencies from 20 Hz to 520 Hz, a range of orbital periods from 2 to ~2,254 h
and a frequency- and period-dependent range of frequency modulation depths from
0.277 to 100 mHz. This corresponds to a range of projected semi-major axes of
the orbit from ~0.6e-3 ls to ~6,500 ls assuming the orbit of the binary is
circular. While no plausible candidate gravitational wave events survive the
pipeline, upper limits are set on the analyzed data. The most sensitive 95%
confidence upper limit obtained on gravitational wave strain is 2.3e-24 at 217
Hz, assuming the source waves are circularly polarized. Although this search
has been optimized for circular binary orbits, the upper limits obtained remain
valid for orbital eccentricities as large as 0.9. In addition, upper limits are
placed on continuous gravitational wave emission from the low-mass x-ray binary
Scorpius X-1 between 20 Hz and 57.25 Hz.Comment: 16 pages, 6 figure
Multimessenger Search for Sources of Gravitational Waves and High-Energy Neutrinos: Results for Initial LIGO-Virgo and IceCube
We report the results of a multimessenger search for coincident signals from
the LIGO and Virgo gravitational-wave observatories and the partially completed
IceCube high-energy neutrino detector, including periods of joint operation
between 2007-2010. These include parts of the 2005-2007 run and the 2009-2010
run for LIGO-Virgo, and IceCube's observation periods with 22, 59 and 79
strings. We find no significant coincident events, and use the search results
to derive upper limits on the rate of joint sources for a range of source
emission parameters. For the optimistic assumption of gravitational-wave
emission energy of \,Mc at \,Hz with \,ms duration, and high-energy neutrino emission of \,erg
comparable to the isotropic gamma-ray energy of gamma-ray bursts, we limit the
source rate below \,Mpcyr. We also examine
how combining information from gravitational waves and neutrinos will aid
discovery in the advanced gravitational-wave detector era
FIRST SEARCHES FOR OPTICAL COUNTERPARTS TO GRAVITATIONAL-WAVE CANDIDATE EVENTS
During the LIGO and Virgo joint science runs in 2009-2010, gravitational wave (GW) data from three interferometer detectors were analyzed within minutes to select GW candidate events and infer their apparent sky positions. Target coordinates were transmitted to several telescopes for follow-up observations aimed at the detection of an associated optical transient. Images were obtained for eight such GW candidates. We present the methods used to analyze the image data as well as the transient search results. No optical transient was identified with a convincing association with any of these candidates, and none of the GW triggers showed strong evidence for being astrophysical in nature. We compare the sensitivities of these observations to several model light curves from possible sources of interest, and discuss prospects for future joint GW-optical observations of this type
Searching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors
Searches for a stochastic gravitational-wave background (SGWB) using terrestrial detectors typically involve cross-correlating data from pairs of detectors. The sensitivity of such cross-correlation analyses depends, among other things, on the separation between the two detectors: the smaller the separation, the better the sensitivity. Hence, a colocated detector pair is more sensitive to a gravitational-wave background than a noncolocated detector pair. However, colocated detectors are also expected to suffer from correlated noise from instrumental and environmental effects that could contaminate the measurement of the background. Hence, methods to identify and mitigate the effects of correlated noise are necessary to achieve the potential increase in sensitivity of colocated detectors. Here we report on the first SGWB analysis using the two LIGO Hanford detectors and address the complications arising from correlated environmental noise. We apply correlated noise identification and mitigation techniques to data taken by the two LIGO Hanford detectors, H1 and H2, during LIGOâs fifth science run. At low frequencies, 40â460 Hz, we are unable to sufficiently mitigate the correlated noise to a level where we may confidently measure or bound the stochastic gravitational-wave signal. However, at high frequencies, 460â1000 Hz, these techniques are sufficient to set a 95% confidence level upper limit on the gravitational-wave energy density of Ω(f) < 7.7 Ă 10[superscript -4](f/900ââHz)[superscript 3], which improves on the previous upper limit by a factor of ~180. In doing so, we demonstrate techniques that will be useful for future searches using advanced detectors, where correlated noise (e.g., from global magnetic fields) may affect even widely separated detectors.National Science Foundation (U.S.)United States. National Aeronautics and Space AdministrationCarnegie TrustDavid & Lucile Packard FoundationAlfred P. Sloan Foundatio
Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts
Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (~10â1000 s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGOâs fifth science run, and GRB triggers from the Swift experiment, we perform a search for unmodeled long-lived GW transients. Finding no evidence of GW emission, we place 90% confidence-level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from F<3:5 ergs cmâ»2 to F<1200 ergs cmâ»2, depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as â 33 Mpc. Advanced detectors are expected to achieve strain sensitivities 10Ă better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs.J. Aasi ... D.J. Hosken ... W. Kim ... E.J. King ... J. Munch ... D. J. Ottaway ... P. J. Veitc
A Serial Commutator Fast Fourier Transform Architecture for Real-Valued Signals
This brief presents a novel pipelined architecture to compute the fast Fourier transform of real input signals in a serial manner, i.e., one sample is processed per cycle. The proposed architecture, referred to as real-valued serial commutator, achieves full hardware utilization by mapping each stage of the fast Fourier transform (FFT) to a half-butterfly operation that operates on real input signals. Prior serial architectures to compute FFT of real signals only achieved 50% hardware utilization. Novel data-exchange and data-reordering circuits are also presented. The complete serial commutator architecture requires 2 log(2) N - 2 real adders, log(2) N - 2 real multipliers, and N + 9 log(2) N - 19 real delay elements, where N represents the size of the FFT.Funding Agencies|Swedish ELLIIT Program</p