319 research outputs found
Finiteness results for Abelian tree models
Equivariant tree models are statistical models used in the reconstruction of
phylogenetic trees from genetic data. Here equivariant refers to a symmetry
group imposed on the root distribution and on the transition matrices in the
model. We prove that if that symmetry group is Abelian, then the Zariski
closures of these models are defined by polynomial equations of bounded degree,
independent of the tree. Moreover, we show that there exists a polynomial-time
membership test for that Zariski closure. This generalises earlier results on
tensors of bounded rank, which correspond to the case where the group is
trivial, and implies a qualitative variant of a quantitative conjecture by
Sturmfels and Sullivant in the case where the group and the alphabet coincide.
Our proofs exploit the symmetries of an infinite-dimensional projective limit
of Abelian star models.Comment: 27 pages. arXiv admin note: substantial text overlap with
arXiv:1103.533
Polynomials and tensors of bounded strength
Notions of rank abound in the literature on tensor decomposition. We prove
that strength, recently introduced for homogeneous polynomials by
Ananyan-Hochster in their proof of Stillman's conjecture and generalised here
to other tensors, is universal among these ranks in the following sense: any
non-trivial Zariski-closed condition on tensors that is functorial in the
underlying vector space implies bounded strength. This generalises a theorem by
Derksen-Eggermont-Snowden on cubic polynomials, as well as a theorem by
Kazhdan-Ziegler which says that a polynomial all of whose directional
derivatives have bounded strength must itself have bounded strength.Comment: Improved the bounds on strength as a function of the dimension of the
space where one first sees nontrivial equations for the tensor property
Noetherianity for infinite-dimensional toric varieties
We consider a large class of monomial maps respecting an action of the
infinite symmetric group, and prove that the toric ideals arising as their
kernels are finitely generated up to symmetry. Our class includes many
important examples where Noetherianity was recently proved or conjectured. In
particular, our results imply Hillar-Sullivant's Independent Set Theorem and
settle several finiteness conjectures due to Aschenbrenner, Martin del Campo,
Hillar, and Sullivant.
We introduce a matching monoid and show that its monoid ring is Noetherian up
to symmetry. Our approach is then to factorize a more general equivariant
monomial map into two parts going through this monoid. The kernels of both
parts are finitely generated up to symmetry: recent work by
Yamaguchi-Ogawa-Takemura on the (generalized) Birkhoff model provides an
explicit degree bound for the kernel of the first part, while for the second
part the finiteness follows from the Noetherianity of the matching monoid ring.Comment: 20 page
On the ideals of equivariant tree models
We introduce equivariant tree models in algebraic statistics, which unify and
generalise existing tree models such as the general Markov model, the strand
symmetric model, and group based models. We focus on the ideals of such models.
We show how the ideals for general trees can be determined from the ideals for
stars. The main novelty is our proof that this procedure yields the entire
ideal, not just an ideal defining the model set-theoretically. A corollary of
theoretical importance is that the ideal for a general tree is generated by the
ideals of its flattenings at vertices.Comment: 23 pages. Greatly improved exposition, in part following suggestions
by a referee--thanks! Also added exampl
Population-based mammography screening below age 50: balancing radiation-induced vs prevented breast cancer deaths
Introduction:Exposure to ionizing radiation at mammography screening may cause breast cancer. Because the radiation risk increases with lower exposure age, advancing the lower age limit may affect the balance between screening benefits and risks. The present study explores the benefit-risk ratio of screening before age 50.Methods:The benefits of biennial mammography screening, starting at various ages between 40 and 50, and continuing up to age 74 were examined using micro-simulation. In contrast with previous studies that commonly used excess relative risk models, we assessed the radiation risks using the latest BEIR-VII excess abso
Polarizations and Nullcone of Representations of Reductive Groups
The paper starts with the following simple observation. Let V be a representation of a reductive group G, and let f_1,f_2,...,f_n be homogeneous invariant functions. Then the polarizations of f_1,f_2,...,f_n define the nullcone of k 0} h(t) x = 0 for all x in L. This is then applied to many examples. A surprising result is about the group SL(2,C) where almost all representations V have the property that all linear subspaces of the nullcone are annihilated. Again, this has interesting applications to the invariants on several copies. Another result concerns the n-qubits which appear in quantum computing. This is the representation of a product of n copies of on the n-fold tensor product C^2 otimes C^2 otimes ... otimes C^2. Here we show just the opposite, namely that the polarizations never define the nullcone of several copies if n <= 3. (An earlier version of this paper, distributed in 2002, was split into two parts; the first part with the title ``On the nullcone of representations of reductive groups'' is published in Pacific J. Math. {bf 224} (2006), 119--140.
Overdetection, overtreatment and costs in prostate-specific antigen screening for prostate cancer
Background:Prostate cancer screening with prostate-specific antigen (PSA) has shown to reduce prostate cancer mortality in the European Randomised study of Screening for Prostate Cancer (ERSPC) trial. Overdetection and overtreatment are substantial unfavourable side effects with consequent healthcare costs. In this study the effects of introducing widespread PSA screening is evaluated.Methods:The MISCAN model was used to simulate prostate cancer growth and detection in a simulated cohort of 100 000 men (European standard population) over 25 years. PSA screening from age 55 to 70 or 75, with 1, 2 and 4-year-intervals is simulated. Number of diagnoses, PSA tests, biopsies, treatments, deaths and corresponding costs for 100 000 men and for United Kingdom and United States are compared.Results:Without screening 2378 men per 100 000 were predicted to be diagnosed with prostate cancer compared with 4956 men after screening at 4-year intervals. By introducing screening, the costs would increase with 100% to \[euro]60 695 000. Overdetection is related to 39% of total costs (\[euro]23 669 000). Screening until age 75 is relatively most expensive because of the costs of overtreatment.Conclusion:Introduction of PSA screening will increase total healthcare costs for prostate cancer substantially, of which the actual screening costs will be a small part
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