30,462 research outputs found
backShift: Learning causal cyclic graphs from unknown shift interventions
We propose a simple method to learn linear causal cyclic models in the
presence of latent variables. The method relies on equilibrium data of the
model recorded under a specific kind of interventions ("shift interventions").
The location and strength of these interventions do not have to be known and
can be estimated from the data. Our method, called backShift, only uses second
moments of the data and performs simple joint matrix diagonalization, applied
to differences between covariance matrices. We give a sufficient and necessary
condition for identifiability of the system, which is fulfilled almost surely
under some quite general assumptions if and only if there are at least three
distinct experimental settings, one of which can be pure observational data. We
demonstrate the performance on some simulated data and applications in flow
cytometry and financial time series. The code is made available as R-package
backShift
Fast, Accurate and Detailed NoC Simulations
Network-on-Chip (NoC) architectures have a wide variety of parameters that can be adapted to the designer's requirements. Fast exploration of this parameter space is only possible at a high-level and several methods have been proposed. Cycle and bit accurate simulation is necessary when the actual router's RTL description needs to be evaluated and verified. However, extensive simulation of the NoC architecture with cycle and bit accuracy is prohibitively time consuming. In this paper we describe a simulation method to simulate large parallel homogeneous and heterogeneous network-on-chips on a single FPGA. The method is especially suitable for parallel systems where lengthy cycle and bit accurate simulations are required. As a case study, we use a NoC that was modelled and simulated in SystemC. We simulate the same NoC on the described FPGA simulator. This enables us to observe the NoC behavior under a large variety of traffic patterns. Compared with the SystemC simulation we achieved a speed-up of 80-300, without compromising the cycle and bit level accuracy
Relaxing state-access constraints in stateful programmable data planes
Supporting the programming of stateful packet forwarding functions in
hardware has recently attracted the interest of the research community. When
designing such switching chips, the challenge is to guarantee the ability to
program functions that can read and modify data plane's state, while keeping
line rate performance and state consistency. Current state-of-the-art designs
are based on a very conservative all-or-nothing model: programmability is
limited only to those functions that are guaranteed to sustain line rate, with
any traffic workload. In effect, this limits the maximum time to execute state
update operations. In this paper, we explore possible options to relax these
constraints by using simulations on real traffic traces. We then propose a
model in which functions can be executed in a larger but bounded time, while
preventing data hazards with memory locking. We present results showing that
such flexibility can be supported with little or no throughput degradation.Comment: 6 page
Digital Switching in the Quantum Domain
In this paper, we present an architecture and implementation algorithm such
that digital data can be switched in the quantum domain. First we define the
connection digraph which can be used to describe the behavior of a switch at a
given time, then we show how a connection digraph can be implemented using
elementary quantum gates. The proposed mechanism supports unicasting as well as
multicasting, and is strict-sense non-blocking. It can be applied to perform
either circuit switching or packet switching. Compared with a traditional space
or time domain switch, the proposed switching mechanism is more scalable.
Assuming an n-by-n quantum switch, the space consumption grows linearly, i.e.
O(n), while the time complexity is O(1) for unicasting, and O(log n) for
multicasting. Based on these advantages, a high throughput switching device can
be built simply by increasing the number of I/O ports.Comment: 24 pages, 16 figures, LaTe
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