6,061 research outputs found
Mixed-Integer Convex Nonlinear Optimization with Gradient-Boosted Trees Embedded
Decision trees usefully represent sparse, high dimensional and noisy data.
Having learned a function from this data, we may want to thereafter integrate
the function into a larger decision-making problem, e.g., for picking the best
chemical process catalyst. We study a large-scale, industrially-relevant
mixed-integer nonlinear nonconvex optimization problem involving both
gradient-boosted trees and penalty functions mitigating risk. This
mixed-integer optimization problem with convex penalty terms broadly applies to
optimizing pre-trained regression tree models. Decision makers may wish to
optimize discrete models to repurpose legacy predictive models, or they may
wish to optimize a discrete model that particularly well-represents a data set.
We develop several heuristic methods to find feasible solutions, and an exact,
branch-and-bound algorithm leveraging structural properties of the
gradient-boosted trees and penalty functions. We computationally test our
methods on concrete mixture design instance and a chemical catalysis industrial
instance
Universal Interface of TAUOLA Technical and Physics Documentation
Because of their narrow width, tau decays can be well separated from their
production process. Only spin degrees of freedom connect these two parts of the
physics process of interest for high energy collision experiments. In the
following, we present a Monte Carlo algorithm which is based on that property.
The interface supplements events generated by other programs, with tau decays.
Effects of spin, genuine weak corrections or of new physics may be taken into
account at the time when a tau decay is generated and written into an event
record.Comment: 1+44 pages, 17 eps figure
Supersymmetric Signatures at an Collider
High energy electron-photon colliders provide unique opportunities for
probing physics beyond the standard model. We have studied the experimental
signatures for two supersymmetric scenarios, with the lightest supersymmetric
particle (LSP) being either the lightest neutralino or the gravitino. In the
``neutralino LSP'' scenario favored by the minimal supersymmetric standard
model (MSSM), it is found that some basic parameters of the model, ,
, and , may be uniquely determined from the outgoing
electron energy spectrum without assuming high scale unification of the masses
or couplings. In the ``gravitino LSP'' scenario which occurs naturally in
models of low energy dynamical supersymmetry breaking, it is possible to have
background-free signatures if the next-to-lightest supersymmetric particle
(NLSP) has a long decay length. In cases that the NLSP decays quickly, ways to
distinguish among the experimental signatures of the two scenarios and of the
standard model (SM) background are discussed.Comment: 14 pages, LaTex file, 3 figure
The Matrix Element Method and QCD Radiation
The matrix element method (MEM) has been extensively used for the analysis of
top-quark and W-boson physics at the Tevatron, but in general without dedicated
treatment of initial state QCD radiation. At the LHC, the increased center of
mass energy leads to a significant increase in the amount of QCD radiation,
which makes it mandatory to carefully account for its effects. We here present
several methods for inclusion of QCD radiation effects in the MEM, and apply
them to mass determination in the presence of multiple invisible particles in
the final state. We demonstrate significantly improved results compared to the
standard treatment.Comment: 15 pp; v2: references and some clarifications added; v3: discussion
of NLO effects, version published in PR
How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging
We present the results of applying new object classification techniques to
difference images in the context of the Nearby Supernova Factory supernova
search. Most current supernova searches subtract reference images from new
images, identify objects in these difference images, and apply simple threshold
cuts on parameters such as statistical significance, shape, and motion to
reject objects such as cosmic rays, asteroids, and subtraction artifacts.
Although most static objects subtract cleanly, even a very low false positive
detection rate can lead to hundreds of non-supernova candidates which must be
vetted by human inspection before triggering additional followup. In comparison
to simple threshold cuts, more sophisticated methods such as Boosted Decision
Trees, Random Forests, and Support Vector Machines provide dramatically better
object discrimination. At the Nearby Supernova Factory, we reduced the number
of non-supernova candidates by a factor of 10 while increasing our supernova
identification efficiency. Methods such as these will be crucial for
maintaining a reasonable false positive rate in the automated transient alert
pipelines of upcoming projects such as PanSTARRS and LSST.Comment: 25 pages; 6 figures; submitted to Ap
Directed Hamiltonicity and Out-Branchings via Generalized Laplacians
We are motivated by a tantalizing open question in exact algorithms: can we
detect whether an -vertex directed graph has a Hamiltonian cycle in time
significantly less than ? We present new randomized algorithms that
improve upon several previous works:
1. We show that for any constant and prime we can count the
Hamiltonian cycles modulo in
expected time less than for a constant that depends only on and
. Such an algorithm was previously known only for the case of counting
modulo two [Bj\"orklund and Husfeldt, FOCS 2013].
2. We show that we can detect a Hamiltonian cycle in
time and polynomial space, where is the size of the maximum
independent set in . In particular, this yields an time
algorithm for bipartite directed graphs, which is faster than the
exponential-space algorithm in [Cygan et al., STOC 2013].
Our algorithms are based on the algebraic combinatorics of "incidence
assignments" that we can capture through evaluation of determinants of
Laplacian-like matrices, inspired by the Matrix--Tree Theorem for directed
graphs. In addition to the novel algorithms for directed Hamiltonicity, we use
the Matrix--Tree Theorem to derive simple algebraic algorithms for detecting
out-branchings. Specifically, we give an -time randomized algorithm
for detecting out-branchings with at least internal vertices, improving
upon the algorithms of [Zehavi, ESA 2015] and [Bj\"orklund et al., ICALP 2015].
We also present an algebraic algorithm for the directed -Leaf problem, based
on a non-standard monomial detection problem
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