175 research outputs found
Quantization-Aware NN Layers with High-throughput FPGA Implementation for Edge AI
Over the past few years, several applications have been extensively exploiting the advantages of deep learning, in particular when using convolutional neural networks (CNNs). The intrinsic flexibility of such models makes them widely adopted in a variety of practical applications, from medical to industrial. In this latter scenario, however, using consumer Personal Computer (PC) hardware is not always suitable for the potential harsh conditions of the working environment and the strict timing that industrial applications typically have. Therefore, the design of custom FPGA (Field Programmable Gate Array) solutions for network inference is gaining massive attention from researchers and companies as well. In this paper, we propose a family of network architectures composed of three kinds of custom layers working with integer arithmetic with a customizable precision (down to just two bits). Such layers are designed to be effectively trained on classical GPUs (Graphics Processing Units) and then synthesized to FPGA hardware for real-time inference. The idea is to provide a trainable quantization layer, called Requantizer, acting both as a non-linear activation for neurons and a value rescaler to match the desired bit precision. This way, the training is not only quantization-aware, but also capable of estimating the optimal scaling coefficients to accommodate both the non-linear nature of the activations and the constraints imposed by the limited precision. In the experimental section, we test the performance of this kind of model while working both on classical PC hardware and a case-study implementation of a signal peak detection device running on a real FPGA. We employ TensorFlow Lite for training and comparison, and use Xilinx FPGAs and Vivado for synthesis and implementation. The results show an accuracy of the quantized networks close to the floating point version, without the need for representative data for calibration as in other approaches, and performance that is better than dedicated peak detection algorithms. The FPGA implementation is able to run in real time at a rate of four gigapixels per second with moderate hardware resources, while achieving a sustained efficiency of 0.5 TOPS/W (tera operations per second per watt), in line with custom integrated hardware accelerators
Feedback Loops Between Fields and Underlying Space Curvature: an Augmented Lagrangian Approach
We demonstrate a systematic implementation of coupling between a scalar field
and the geometry of the space (curve, surface, etc.) which carries the field.
This naturally gives rise to a feedback mechanism between the field and the
geometry. We develop a systematic model for the feedback in a general form,
inspired by a specific implementation in the context of molecular dynamics (the
so-called Rahman-Parrinello molecular dynamics, or RP-MD). We use a generalized
Lagrangian that allows for the coupling of the space's metric tensor (the first
fundamental form) to the scalar field, and add terms motivated by RP-MD. We
present two implementations of the scheme: one in which the metric is only
time-dependent [which gives rise to ordinary differential equation (ODE) for
its temporal evolution], and one with spatio-temporal dependence [wherein the
metric's evolution is governed by a partial differential equation (PDE)].
Numerical results are reported for the (1+1)-dimensional model with a
nonlinearity of the sine-Gordon type.Comment: 5 pages, 3 figures, Phys. Rev. E in pres
String Method for the Study of Rare Events
We present a new and efficient method for computing the transition pathways,
free energy barriers, and transition rates in complex systems with relatively
smooth energy landscapes. The method proceeds by evolving strings, i.e. smooth
curves with intrinsic parametrization whose dynamics takes them to the most
probable transition path between two metastable regions in the configuration
space. Free energy barriers and transition rates can then be determined by
standard umbrella sampling technique around the string. Applications to
Lennard-Jones cluster rearrangement and thermally induced switching of a
magnetic film are presented.Comment: 4 pages, 4 figure
(Meta-)stable reconstructions of the diamond(111) surface: interplay between diamond- and graphite-like bonding
Off-lattice Grand Canonical Monte Carlo simulations of the clean diamond
(111) surface, based on the effective many-body Brenner potential, yield the
Pandey reconstruction in agreement with \emph{ab-initio}
calculations and predict the existence of new meta-stable states, very near in
energy, with all surface atoms in three-fold graphite-like bonding. We believe
that the long-standing debate on the structural and electronic properties of
this surface could be solved by considering this type of carbon-specific
configurations.Comment: 4 pages + 4 figures, Phys. Rev. B Rapid Comm., in press (15Apr00).
For many additional details (animations, xyz files) see electronic supplement
to this paper at http://www.sci.kun.nl/tvs/carbon/meta.htm
Variable Curvature Slab Molecular Dynamics as a Method to Determine Surface Stress
A thin plate or slab, prepared so that opposite faces have different surface
stresses, will bend as a result of the stress difference. We have developed a
classical molecular dynamics (MD) formulation where (similar in spirit to
constant-pressure MD) the curvature of the slab enters as an additional
dynamical degree of freedom. The equations of motion of the atoms have been
modified according to a variable metric, and an additional equation of motion
for the curvature is introduced. We demonstrate the method to Au surfaces, both
clean and covered with Pb adsorbates, using many-body glue potentials.
Applications to stepped surfaces, deconstruction and other surface phenomena
are under study.Comment: 16 pages, 8 figures, REVTeX, submitted to Physical Review
Action-derived molecular dynamics in the study of rare events
We present a practical method to generate classical trajectories with fixed
initial and final boundary conditions. Our method is based on the minimization
of a suitably defined discretized action. The method finds its most natural
application in the study of rare events. Its capabilities are illustrated by
non-trivial examples. The algorithm lends itself to straightforward
parallelization, and when combined with molecular dynamics (MD) it promises to
offer a powerful tool for the study of chemical reactions.Comment: 7 Pages, 4 Figures (3 in color), submitted to Phys. Rev. Let
Investigating Rare Events by Transition Interface Sampling
We briefly review simulation schemes for the investigation of rare
transitions and we resume the recently introduced Transition Interface
Sampling, a method in which the computation of rate constants is recast into
the computation of fluxes through interfaces dividing the reactant and product
state.Comment: 12 pages, 1 figure, contributed paper to the proceedings of NEXT
2003, Second Sardinian International Conference on News and Expectations in
Thermostatistics, 21-28 Sep 2003, Cagliari (Italy
Combining Optimal Control Theory and Molecular Dynamics for Protein Folding
A new method to develop low-energy folding routes for proteins is presented. The novel aspect of the proposed approach is the synergistic use of optimal control theory with Molecular Dynamics (MD). In the first step of the method, optimal control theory is employed to compute the force field and the optimal folding trajectory for the atoms of a Coarse-Grained (CG) protein model. The solution of this CG optimization provides an harmonic approximation of the true potential energy surface around the native state. In the next step CG optimization guides the MD simulation by specifying the optimal target positions for the atoms. In turn, MD simulation provides an all-atom conformation whose positions match closely the reference target positions determined by CG optimization. This is accomplished by Targeted Molecular Dynamics (TMD) which uses a bias potential or harmonic restraint in addition to the usual MD potential. Folding is a dynamical process and as such residues make different contacts during the course of folding. Therefore CG optimization has to be reinitialized and repeated over time to accomodate these important changes. At each sampled folding time, the active contacts among the residues are recalculated based on the all-atom conformation obtained from MD. Using the new set of contacts, the CG potential is updated and the CG optimal trajectory for the atoms is recomputed. This is followed by MD. Implementation of this repetitive CG optimization - MD simulation cycle generates the folding trajectory. Simulations on a model protein Villin demonstrate the utility of the method. Since the method is founded on the general tools of optimal control theory and MD without any restrictions, it is widely applicable to other systems. It can be easily implemented with available MD software packages
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