156 research outputs found
Covariance estimation for distributions with moments
We study the minimal sample size N=N(n) that suffices to estimate the
covariance matrix of an n-dimensional distribution by the sample covariance
matrix in the operator norm, with an arbitrary fixed accuracy. We establish the
optimal bound N=O(n) for every distribution whose k-dimensional marginals have
uniformly bounded moments outside the sphere of radius
. In the specific case of log-concave distributions, this result
provides an alternative approach to the Kannan-Lovasz-Simonovits problem, which
was recently solved by Adamczak et al. [J. Amer. Math. Soc. 23 (2010) 535-561].
Moreover, a lower estimate on the covariance matrix holds under a weaker
assumption - uniformly bounded moments of one-dimensional
marginals. Our argument consists of randomizing the spectral sparsifier, a
deterministic tool developed recently by Batson, Spielman and Srivastava [SIAM
J. Comput. 41 (2012) 1704-1721]. The new randomized method allows one to
control the spectral edges of the sample covariance matrix via the Stieltjes
transform evaluated at carefully chosen random points.Comment: Published in at http://dx.doi.org/10.1214/12-AOP760 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org
An Alon-Boppana Type Bound for Weighted Graphs and Lowerbounds for Spectral Sparsification
We prove the following Alon-Boppana type theorem for general (not necessarily
regular) weighted graphs: if is an -node weighted undirected graph of
average combinatorial degree (that is, has edges) and girth , and if are the
eigenvalues of the (non-normalized) Laplacian of , then (The Alon-Boppana theorem implies that if is unweighted and
-regular, then if the diameter is at least .)
Our result implies a lower bound for spectral sparsifiers. A graph is a
spectral -sparsifier of a graph if where is the Laplacian matrix of and is
the Laplacian matrix of . Batson, Spielman and Srivastava proved that for
every there is an -sparsifier of average degree where
and the edges of are a
(weighted) subset of the edges of . Batson, Spielman and Srivastava also
show that the bound on cannot be reduced below when is a clique; our Alon-Boppana-type result implies that
cannot be reduced below when comes
from a family of expanders of super-constant degree and super-constant girth.
The method of Batson, Spielman and Srivastava proves a more general result,
about sparsifying sums of rank-one matrices, and their method applies to an
"online" setting. We show that for the online matrix setting the bound is tight, up to lower order terms
Content Based Document Recommender using Deep Learning
With the recent advancements in information technology there has been a huge
surge in amount of data available. But information retrieval technology has not
been able to keep up with this pace of information generation resulting in over
spending of time for retrieving relevant information. Even though systems exist
for assisting users to search a database along with filtering and recommending
relevant information, but recommendation system which uses content of documents
for recommendation still have a long way to mature. Here we present a Deep
Learning based supervised approach to recommend similar documents based on the
similarity of content. We combine the C-DSSM model with Word2Vec distributed
representations of words to create a novel model to classify a document pair as
relevant/irrelavant by assigning a score to it. Using our model retrieval of
documents can be done in O(1) time and the memory complexity is O(n), where n
is number of documents.Comment: Accepted in ICICI 2017, Coimbatore, Indi
Factors influencing bank deposits : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Banking at Massey University, Palmerston North, New Zealand
This thesis comprises three essays that investigate the effects of human capital, financial markets, and the banking system development on bank deposits, deposit funding, retail, and time deposits proportions. The first two essays are country level studies, whereas the third is at bank level. The data related to first essay has been obtained from the World Bank and the World Health Organisation (WHO). For the second and third essays, bank level data is from Bankscope and macroeconomic variables data are from the World Bank.
The first essay investigates the effects of human capital development on bank deposits, employing 2SLS method in a cross-country setup. Human capital development includes the development of the healthcare system and education level. I use two dependent variables: deposits to GDP ratio and value of total deposits. Results show a positive relationship between human capital development and bank deposits. However, the impact of healthcare system on total deposits is higher than the bank deposits to GDP ratio, suggesting that an improvement in the healthcare system increases households’ income and a proportion of that increased income goes into the banking system. The impact of education is higher in high financially included countries than in less financially included countries.
The second essay examines the effects of financial markets development on bank deposits, using instrumental variables methods. Empirical results suggest that investors in developed and developing economies use financial markets differently. In highly financially integrated economies, the financial markets and banking system complement each other, whereas in fragmented markets they compete.
The third essay explores the effects of competition on bank deposit funding and composition. Interest cost has been used to measure deposit competition and the Herfindahl- Hirschman Index (HHI3) at deposits and loans levels to measure market structure. The results show that increased deposit competition encourages banks to increase the proportion of less costly funds, causing a reduction in deposit funding. In contrast, high interest rates attract retail depositors, especially for time deposits, thereby increasing the proportion of retail deposits. However, this finding varies according to the financial development level of the countries. Market concentration shows negative effects on bank deposit funding and composition
Twice-Ramanujan Sparsifiers
We prove that every graph has a spectral sparsifier with a number of edges
linear in its number of vertices. As linear-sized spectral sparsifiers of
complete graphs are expanders, our sparsifiers of arbitrary graphs can be
viewed as generalizations of expander graphs.
In particular, we prove that for every and every undirected, weighted
graph on vertices, there exists a weighted graph
with at most \ceil{d(n-1)} edges such that for every , where and
are the Laplacian matrices of and , respectively. Thus,
approximates spectrally at least as well as a Ramanujan expander with
edges approximates the complete graph. We give an elementary
deterministic polynomial time algorithm for constructing
- …