10,554 research outputs found
Stability of matrix factorization for collaborative filtering
We study the stability vis a vis adversarial noise of matrix factorization
algorithm for matrix completion. In particular, our results include: (I) we
bound the gap between the solution matrix of the factorization method and the
ground truth in terms of root mean square error; (II) we treat the matrix
factorization as a subspace fitting problem and analyze the difference between
the solution subspace and the ground truth; (III) we analyze the prediction
error of individual users based on the subspace stability. We apply these
results to the problem of collaborative filtering under manipulator attack,
which leads to useful insights and guidelines for collaborative filtering
system design.Comment: ICML201
Maximal Quantum Fisher Information in a Mach-Zehnder Interferometer without initial parity
Mach-Zehnder interferometer is a common device in quantum phase estimation
and the photon losses in it are an important issue for achieving a high phase
accuracy. Here we thoroughly discuss the precision limit of the phase in the
Mach-Zehnder interferometer with a coherent state and a superposition of
coherent states as input states. By providing a general analytical expression
of quantum Fisher information, the phase-matching condition and optimal initial
parity are given. Especially, in the photon loss scenario, the sensitivity
behaviors are analyzed and specific strategies are provided to restore the
phase accuracies for symmetric and asymmetric losses.Comment: 10 pages, 3 figure
Chandra Observation of a Weak Shock in the Galaxy Cluster A2556
Based on a 21.5 ks \chandra\ observation of A2556, we identify an edge on the
surface brightness profile (SBP) at about 160 kpc northeast of the
cluster center, and it corresponds to a shock front whose Mach number
is calculated to be . No prominent
substructure, such as sub-cluster, is found in either optical or X-ray band
that can be associated with the edge, suggesting that the conventional
super-sonic motion mechanism may not work in this case. As an alternative
solution, we propose that the nonlinear steepening of acoustic wave, which is
induced by the turbulence of the ICM at the core of the cluster, can be used to
explain the origin of the shock front. Although nonlinear steepening weak shock
is expected to occur frequently in clusters, why it is rarely observed still
remains a question that requires further investigation, including both deeper
X-ray observation and extensive theoretical studies.Comment: 15 pages, 4 figures, accepted by Ap
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