A partially collapsed Gibbs sampler for Bayesian quantile regression

We introduce a set of new Gibbs sampler for Bayesian analysis of quantile re-gression model. The new algorithm, which partially collapsing an ordinary Gibbs sampler, is called Partially Collapsed Gibbs (PCG) sampler. Although the Metropolis-Hastings algorithm has been employed in Bayesian quantile regression, including median regression, PCG has superior convergence properties to an ordinary Gibbs sampler. Moreover, Our PCG sampler algorithm, which is based on a theoretic derivation of an asymmetric Laplace as scale mixtures of normal distributions, requires less computation than the ordinary Gibbs sampler and can significantly reduce the computation involved in approximating the Bayes Factor and marginal likelihood. Like the ordinary Gibbs sampler, the PCG sample can also be used to calculate any associated marginal and predictive distributions. The quantile regression PCG sampler is illustrated by analysing simulated data and the data of length of stay in hospital. The latter provides new insight into hospital perfor-mance. C-code along with an R interface for our algorithms is publicly available on request from the first author. JEL classification: C11, C14, C21, C31, C52, C53

Do Shareholders' Preferences Affect their Funds' Management? Evidence from the Cross Section of Shareholders and Funds

We consider how fund managers respond to the conflicting preferences of their investors. We focus on the conflict between the taxable and retirement accounts of international funds, which face different tradeoffs between dividends and capital gains. In principle, managers could resolve this conflict through dividend arbitrage, but a proprietary database of dividend-arbitrage transactions shows that in practice they cannot. Thus, managers must resolve it through their investment policies, and we find robust evidence that managers with more retirement money favor the preferences of retirement investors. We find additional evidence in the difference between U.S. and Canadian funds' portfolio weights. Nous étudions comment les gestionnaires de fonds réagissent aux préférences contradictoires de leurs investisseurs. Notre étude se concentre principalement sur les conflits entre les comptes taxés et les comptes de retraite des fonds internationaux qui font l'objet de compromis différents entre les gains en dividendes et les gains de capital. En théorie, les gestionnaires peuvent résoudre ces conflits par des opérations d'arbitrage sur les dividendes, mais une base de données privée d'opérations d'arbitrage fait apparaître qu'en pratique ils ne peuvent pas. Les gestionnaires doivent alors résoudre ces conflits à travers leurs politiques d'investissement, et nous trouvons des résultats significatifs montrant que ceux dont le capital est issu majoritairement des retraites favorisent les investisseurs de fonds de pension. Nous trouvons également des différences entre les poids des portefeuilles de fonds américains et canadiens.Dividend arbitrage, tax efficiency, agency issues, mutual funds, arbitrage sur les dividendes, taxes sur les rendements, placements pour compte, fonds commun de placement

How and Why do Investors Trade Votes, and What Does it Mean?

The standard analysis of corporate governance is that shareholders vote in the ratios that firms choose, such as one-share-one-vote. But if the cost of unbundling and trading votes is sufficiently low, then shareholders vote in the ratios that they themselves choose. We document an active market for votes within the equity-loan market, where we find that the average vote sells for zero. We hypothesize that asymmetric information motivates these vote reallocations, and we find support for this view in the cross section of votes: there is more trade for higher-spread firms and more for poor performers, especially when the vote is close. We also find that the vote reallocations correspond to support for shareholder proposals and opposition to management proposals. L'analyse classique de la gouvernance d'entreprise suppose que les actionnaires votent selon les modalités choisies par la firme, par exemple un vote par action. Mais si les coûts associés à la séparation et à l'échange des votes sont suffisamment faibles, alors les actionnaires votent selon les modalités qu'ils ont eux-mêmes choisies. Nous présentons le cas d'un marché actif de votes au sein du marché des mises de fonds sous forme d'emprunts (equity loans), où nous constatons qu'en moyenne les votes se vendent pour rien. Nous supposons que l'asymétrie d'information provoque cette réallocation des votes, et nous étayons cette hypothèse à travers l'étude transversale des votes : le nombre d'opérations est plus important pour les compagnies dont l'écart acheteur-vendeur est plus élevé ainsi que pour celles dont les résultats sont plus faibles, particulièrement lorsque le vote est clos. Cette étude montre aussi que la réallocation des votes permet de soutenir les propositions des actionnaires et de s'opposer à celles des gestionnaires.vote trading, corporate governance, equity lending, information asymmetry, transaction de votes, gouvernance d'entreprise, prêt d'actions, asymétrie d'information

VLSI architectures for computing multiplications and inverses in GF(2-m)

Finite field arithmetic logic is central in the implementation of Reed-Solomon coders and in some cryptographic algorithms. There is a need for good multiplication and inversion algorithms that are easily realized on VLSI chips. Massey and Omura recently developed a new multiplication algorithm for Galois fields based on a normal basis representation. A pipeline structure is developed to realize the Massey-Omura multiplier in the finite field GF(2m). With the simple squaring property of the normal-basis representation used together with this multiplier, a pipeline architecture is also developed for computing inverse elements in GF(2m). The designs developed for the Massey-Omura multiplier and the computation of inverse elements are regular, simple, expandable and, therefore, naturally suitable for VLSI implementation

The a priori Tan Theta Theorem for spectral subspaces

Let A be a self-adjoint operator on a separable Hilbert space H. Assume that the spectrum of A consists of two disjoint components s_0 and s_1 such that the set s_0 lies in a finite gap of the set s_1. Let V be a bounded self-adjoint operator on H off-diagonal with respect to the partition spec(A)=s_0 \cup s_1. It is known that if ||V||<\sqrt{2}d, where d=\dist(s_0,s_1), then the perturbation V does not close the gaps between s_0 and s_1 and the spectrum of the perturbed operator L=A+V consists of two isolated components s'_0 and s'_1 grown from s_0 and s_1, respectively. Furthermore, it is known that if V satisfies the stronger bound ||V||< d then the following sharp norm estimate holds: ||E_L(s'_0)-E_A(s_0)|| \leq sin(arctan(||V||/d)), where E_A(s_0) and E_L(s'_0) are the spectral projections of A and L associated with the spectral sets s_0 and s'_0, respectively. In the present work we prove that this estimate remains valid and sharp also for d \leq ||V||< \sqrt{2}d, which completely settles the issue.Comment: v3: some typos fixed; Examples adde

A parallel VLSI architecture for a digital filter of arbitrary length using Fermat number transforms

A parallel architecture for computation of the linear convolution of two sequences of arbitrary lengths using the Fermat number transform (FNT) is described. In particular a pipeline structure is designed to compute a 128-point FNT. In this FNT, only additions and bit rotations are required. A standard barrel shifter circuit is modified so that it performs the required bit rotation operation. The overlap-save method is generalized for the FNT to compute a linear convolution of arbitrary length. A parallel architecture is developed to realize this type of overlap-save method using one FNT and several inverse FNTs of 128 points. The generalized overlap save method alleviates the usual dynamic range limitation in FNTs of long transform lengths. Its architecture is regular, simple, and expandable, and therefore naturally suitable for VLSI implementation

Parasitism, Adult Emergence, Sex Ratio, and Size of \u3ci\u3eAphidius Colemani\u3c/i\u3e (Hymenoptera: Aphidiidae) on Several Aphid Species

Aphidius colemani Viereck parasitizes several economically important aphid pests of small grain crops including the greenbug, Schizaphis graminum and the Russian wheat aphid, Diuraphis noxia. The ability of A. colemani to switch from S. graminum to several species of aphids common to agricultural and associated non-agricultural ecosystems in the Great Plains, and the effects of host-change on several biological parameters that influence population growth rate were determined. Female A. colemani parasitized and developed to adulthood in nine of 14 aphid species to which they were exposed in the laboratory. All small grain feeding aphids except Sipha flava were parasi­tized. Two sunflower feeding species (Aphis nerii and A. helianthi) and two crucifer feeding species (Lipaphis erysimi and Brevicoryne brassicae) were parasitized, as was the cotton aphid. Aphis gossypii. The average percentage of aphids parasitized differed significantly among host aphid species. as did the percentage of parasitoids surviving from the mummy to the adult stage and the time required for immature development. The sex ratio of adults that enclosed from the various hosts did not differ significantly among species. Dry weights of adult parasitoids differed significantly among host species. Adults from S. graminum weighed most (0.054 mg) while those emerging from A. helianthi weighed least (0.020 mg). Results are discussed in terms of strategies for classical biological control of aphid pests of cereals

Quantum cosmology of scalar-tensor theories and self-adjointness

In this paper, the problem of the self-adjointness for the case of a quantum minisuperspace Hamiltonian retrieved from a Brans-Dicke (BD) action is investigated. Our matter content is presented in terms of a perfect fluid, onto which the Schutz's formalism will be applied. We use the von Neumann theorem and the similarity with the Laplacian operator in one of the variables to determine the cases where the Hamiltonian is self-adjoint and if it admits self-adjoint extensions. For the latter, we study which extension is physically more suitable.Comment: Latex file, 12 pages. Small changes made in the paper, and a a new appendix adde

Static and dynamic Jahn-Teller effect in the alkali metal fulleride salts A4C60 (A = K, Rb, Cs)

We report the temperature dependent mid- and near-infrared spectra of K4C60, Rb4C60 and Cs4C60. The splitting of the vibrational and electronic transitions indicates a molecular symmetry change of C604- which brings the fulleride anion from D2h to either a D3d or a D5d distortion. In contrast to Cs4C60, low temperature neutron diffraction measurements did not reveal a structural phase transition in either K4C60 and Rb4C60. This proves that the molecular transition is driven by the molecular Jahn-Teller effect, which overrides the distorting potential field of the surrounding cations at high temperature. In K4C60 and Rb4C60 we suggest a transition from a static to a dynamic Jahn-Teller state without changing the average structure. We studied the librations of these two fullerides by temperature dependent inelastic neutron scattering and conclude that both pseudorotation and jump reorientation are present in the dynamic Jahn-Teller state.Comment: 13 pages, 10 figures, to be published in Phys. Rev.