443 research outputs found
Deterministic Nonsmooth Nonconvex Optimization
We study the complexity of optimizing nonsmooth nonconvex Lipschitz functions
by producing -stationary points. Several recent works have
presented randomized algorithms that produce such points using first-order oracle calls, independent of the
dimension . It has been an open problem as to whether a similar result can
be obtained via a deterministic algorithm. We resolve this open problem,
showing that randomization is necessary to obtain a dimension-free rate. In
particular, we prove a lower bound of for any deterministic
algorithm. Moreover, we show that unlike smooth or convex optimization, access
to function values is required for any deterministic algorithm to halt within
any finite time.
On the other hand, we prove that if the function is even slightly smooth,
then the dimension-free rate of can be
obtained by a deterministic algorithm with merely a logarithmic dependence on
the smoothness parameter. Motivated by these findings, we turn to study the
complexity of deterministically smoothing Lipschitz functions. Though there are
efficient black-box randomized smoothings, we start by showing that no such
deterministic procedure can smooth functions in a meaningful manner, resolving
an open question. We then bypass this impossibility result for the structured
case of ReLU neural networks. To that end, in a practical white-box setting in
which the optimizer is granted access to the network's architecture, we propose
a simple, dimension-free, deterministic smoothing that provably preserves
-stationary points. Our method applies to a variety of
architectures of arbitrary depth, including ResNets and ConvNets. Combined with
our algorithm, this yields the first deterministic dimension-free algorithm for
optimizing ReLU networks, circumventing our lower bound.Comment: This work supersedes arxiv:2209.12463 and arxiv:2209.10346[Section
3], with major additional result
Meta-Analysis of Cyber Intimate Partner Violence Perpetration and Victimization: Different Types and their Associations with Face-to-Face IPV among Men and Women
Cyber intimate partner violence (C-IPV) is a technology-mediated form of violence. It has been examined only in the last 10 years as a form of violence that can cause psychological damage to its victims. How this phenomenon connects to and differs from face-to-face IPV (F2F-IPV) has been, as yet, little studied. Research has not made clear whether sex differences may impact its use, particularly in light of the fact that no physical coercion is used in C-IPV. Thus, the current research aimed to investigate through a meta-analysis: differences between the average levels of different types of C-IPV victimization and perpetration; the association between C-IPV and F2F-IPV victimization and perpetration; and whether the answers to these questions were dependent on sex. The current meta-analysis drew on 46 studies, within 44 papers, with a total sample of 27,491 participants. Findings from 22 of these studies showed no significant sex differences between the average levels of different types of C-IPV victimization and between different types of C-IPV perpetration. These 22 studies showed positive large effect sizes for the correlation between C-IPV and F2F-IPV perpetration and victimization. Moreover, in both perpetration and victimization, sex did not impact the level of association. The findings suggested that C-IPV and F2F-IPV are highly correlated, and though not the same, they may share similar characteristics. Additionally, the results suggested that sex differences do not impact non-physical aggression, such as C-IPV. The implications for preventive strategies include that IPV interventions should also focus on alleviating instances of C-IPV
Gemini Near Infrared Spectrograph - Distant Quasar Survey: Prescriptions for Calibrating UV-Based Estimates of Supermassive Black Hole Masses in High-Redshift Quasars
The most reliable single-epoch supermassive black hole mass ()
estimates in quasars are obtained by using the velocity widths of
low-ionization emission lines, typically the H line.
Unfortunately, this line is redshifted out of the optical band at ,
leaving estimates to rely on proxy rest-frame ultraviolet (UV)
emission lines, such as C IV or Mg II , which
contain intrinsic challenges when measuring, resulting in uncertain estimates. In this work, we aim at correcting estimates
derived from the C IV and Mg II emission lines based on estimates derived from
the H emission line. We find that employing the equivalent width of C IV
in deriving estimates based on Mg II and C IV provides values that
are closest to those obtained from H. We also provide prescriptions to
estimate values when only C IV, only Mg II, and both C IV and Mg
II are measurable. We find that utilizing both emission lines, where available,
reduces the scatter of UV-based estimates by when
compared to previous studies. Lastly, we discuss the potential of our
prescriptions to provide more accurate and precise estimates of
given a much larger sample of quasars at , where
both Mg II and H can be measured in the same near-infrared spectrum.Comment: 19 pages (AASTeX 6.3.1), 9 figures, accepted for publication in Ap
Gemini Near Infrared Spectrograph -- Distant Quasar Survey: Augmented Spectroscopic Catalog and a Prescription for Correcting UV-Based Quasar Redshifts
Quasars at most often have redshifts measured from rest-frame
ultraviolet emission lines. One of the most common such lines, C IV
, shows blueshifts up to , and in
rare cases even higher. This blueshifting results in highly uncertain redshifts
when compared to redshift determinations from rest-frame optical emission
lines, e.g., from the narrow [O III] feature. We present
spectroscopic measurements for 260 sources at
having
mag from the Gemini Near Infrared
Spectrograph - Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the
previous iteration which contained 226 of the 260 sources whose measurements
are improved upon in this work. We obtain reliable systemic redshifts based on
[O III] for a subset of 121 sources which we use to calibrate
prescriptions for correcting UV-based redshifts. These prescriptions are based
on a regression analysis involving C IV full-width-at-half-maximum intensity
and equivalent width, along with the UV continuum luminosity at a rest-frame
wavelength of 1350 A. Applying these corrections can improve the accuracy and
the precision in the C IV-based redshift by up to
and , respectively, which correspond to
Mpc and Mpc in comoving distance at . Our prescriptions
also improve the accuracy of the best available multi-feature redshift
determination algorithm by , indicating that the
spectroscopic properties of the C IV emission line can provide robust redshift
estimates for high-redshift quasars. We discuss the prospects of our
prescriptions for cosmological and quasar studies utilizing upcoming large
spectroscopic surveys.Comment: 20 pages (AASTeX 6.3.1), 8 figures, accepted for publication in Ap
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