Enumerating Polytropes

Polytropes are both ordinary and tropical polytopes. We show that tropical types of polytropes in $\mathbb{TP}^{n-1}$ are in bijection with cones of a certain Gr\"{o}bner fan $\mathcal{GF}_n$ in $\mathbb{R}^{n^2 - n}$ restricted to a small cone called the polytrope region. These in turn are indexed by compatible sets of bipartite and triangle binomials. Geometrically, on the polytrope region, $\mathcal{GF}_n$ is the refinement of two fans: the fan of linearity of the polytrope map appeared in \cite{tran.combi}, and the bipartite binomial fan. This gives two algorithms for enumerating tropical types of polytropes: one via a general Gr\"obner fan software such as \textsf{gfan}, and another via checking compatibility of systems of bipartite and triangle binomials. We use these algorithms to compute types of full-dimensional polytropes for $n = 4$, and maximal polytropes for $n = 5$.Comment: Improved exposition, fixed error in reporting the number maximal polytropes for $n = 6$, fixed error in definition of bipartite binomial

HodgeRank is the limit of Perron Rank

We study the map which takes an elementwise positive matrix to the k-th root of the principal eigenvector of its k-th Hadamard power. We show that as $k$ tends to 0 one recovers the row geometric mean vector and discuss the geometric significance of this convergence. In the context of pairwise comparison ranking, our result states that HodgeRank is the limit of Perron Rank, thereby providing a novel mathematical link between two important pairwise ranking methods

Learning Technological Capability for Vietnam's Industrial Upgrading: Challenges of the Globalization.

The paper discusses technological capabilities in Vietnamese industry considering mainly the role of foreign companies. The support of technological change is limited by specific disadvantages of Vietnamese environment, mainly insufficient organizational and legal shortcomings. Thus the connections between foreign and local companies did not produce expected results. The diffusion of technological skills takes place via training process, transfer of tacit and codified knowledge, spillover to local partners and influence absorption capacity of the local market. The cases of ten foreign companies from five different countries are presented. Major conclusions underline the threats of global operations of international companies when they are not supported by enlightened policies of companies and governments in host countries on one side and present the opportunities for these countries economy on the other.FDI; Joint-ventures; technology spillover; technological capabilities; tacit knowledge; low-cost-labor-trap; value chain; technical change

Model Selection with the Loss Rank Principle

A key issue in statistics and machine learning is to automatically select the "right" model complexity, e.g., the number of neighbors to be averaged over in k nearest neighbor (kNN) regression or the polynomial degree in regression with polynomials. We suggest a novel principle - the Loss Rank Principle (LoRP) - for model selection in regression and classification. It is based on the loss rank, which counts how many other (fictitious) data would be fitted better. LoRP selects the model that has minimal loss rank. Unlike most penalized maximum likelihood variants (AIC, BIC, MDL), LoRP depends only on the regression functions and the loss function. It works without a stochastic noise model, and is directly applicable to any non-parametric regressor, like kNN.Comment: 31 LaTeX pages, 1 figur

Antibiotics Time Machine is NP-hard

The antibiotics time machine is an optimization question posed by Mira \latin{et al.} on the design of antibiotic treatment plans to minimize antibiotic resistance. The problem is a variation of the Markov decision process. These authors asked if the problem can be solved efficiently. In this paper, we show that this problem is NP-hard in general.Comment: 5 page