“Welfare Gains and Annuities Demand”

This paper extends the annuity demand theory, giving new reasons for the small annuities demand. Regarding this problem, Yaari (1965) claims, under the condition that no one can die in debt, that a selfish consumer will fully annuitized her savings, insofar as annuity asset yield dominate conventional assets yield. However, we demonstrated mathematically that, in a standard life-cycle model, when borrowings are unconstrained and financial markets are complete, a selfish consumer may prefer not to annuitize her savings. In addition, we analyze the desire to purchase annuities according to the risk aversion coefficient and wealth composition.Annuities Demand; Complete Markets; Myopic-selfish Behavior; Life-cycle Model

The role of demography on per capita output growth and saving rates

Computable OLG growth models and "convergence models" differ in their assessment of the extent to which demography influences economic growth. In this paper, I show that computable OLG growth models produce results similar to those of convergence models when more detailed demographic information is used. To do so, I implement a general equilibrium overlapping generations model to explain Taiwan's economic miracle during the period 1965-2005. I find that Taiwan's demographic transition accounts for 22% of per capita output growth, 16.4% of the investment rate, and 18.5% of the savings rate for the period 1965-2005. Decomposing the demographic effect into its components, I find that fertility alone explains the impact of demographic changes in per capita output growth, while both fertility and mortality explain investment and saving rates. Assuming a small open economy, I find that investment rates increase with more rapid population growth, while saving rates follows the dependence hypothesis (Coale and Hoover, 1958). Under a closed-economy, the population growth rate has a negative influence on economic growth.Taiwan, demography, economic growth

The complexity of general-valued CSPs seen from the other side

The constraint satisfaction problem (CSP) is concerned with homomorphisms between two structures. For CSPs with restricted left-hand side structures, the results of Dalmau, Kolaitis, and Vardi [CP'02], Grohe [FOCS'03/JACM'07], and Atserias, Bulatov, and Dalmau [ICALP'07] establish the precise borderline of polynomial-time solvability (subject to complexity-theoretic assumptions) and of solvability by bounded-consistency algorithms (unconditionally) as bounded treewidth modulo homomorphic equivalence. The general-valued constraint satisfaction problem (VCSP) is a generalisation of the CSP concerned with homomorphisms between two valued structures. For VCSPs with restricted left-hand side valued structures, we establish the precise borderline of polynomial-time solvability (subject to complexity-theoretic assumptions) and of solvability by the $k$-th level of the Sherali-Adams LP hierarchy (unconditionally). We also obtain results on related problems concerned with finding a solution and recognising the tractable cases; the latter has an application in database theory.Comment: v2: Full version of a FOCS'18 paper; improved presentation and small correction

On Low Treewidth Approximations of Conjunctive Queries

We recently initiated the study of approximations of conjunctive queries within classes that admit tractable query evaluation (with respect to combined complexity). Those include classes of acyclic, bounded treewidth, or bounded hypertreewidth queries. Such approximations are always guaranteed to exist. However, while for acyclic and bounded hypertreewidth queries we have shown a number of examples of interesting approximations, for queries of bounded treewidth the study had been restricted to queries over graphs, where such approximations usually trivialize. In this note we show that for relations of arity greater than two, the notion of low treewidth approximations is a rich one, as many queries possess them. In fact we look at approximations of queries of maximum possible treewidth by queries of minimum possible treewidth (i.e., one), and show that even in this case the structure of approximations remain rather rich as long as input relations are not binary

Tècniques de conreu de l'ametller

Hom analitza ací els factors agroclimàtics amb incidència en la producció de l'ametller: temperatura, higrometria, lluminositat y edafologia; i les tècniques de conreu: preparació del sòl, plantació, marcs de plantació, atencions culturals, adobament, reg, poda i recol•lecció. Hom hi inclou, també, un estudi de les despeses de producció.Se analizan los factores agroclimáticos con incidencia en la producción del almendro: temperatura, higrometría, luminosidad y edafología; y las técnicas de cultivo: preparación del suelo, plantación, marcos de plantación, cuidados culturales, abonado, riego, poda y recolección. Se incluye, asimismo, un estudio de los costos de producción

The Complexity of Reverse Engineering Problems for Conjunctive Queries

Reverse engineering problems for conjunctive queries (CQs), such as query by example (QBE) or definability, take a set of user examples and convert them into an explanatory CQ. Despite their importance, the complexity of these problems is prohibitively high (coNEXPTIME-complete). We isolate their two main sources of complexity and propose relaxations of them that reduce the complexity while having meaningful theoretical interpretations. The first relaxation is based on the idea of using existential pebble games for approximating homomorphism tests. We show that this characterizes QBE/definability for CQs up to treewidth k, while reducing the complexity to EXPTIME. As a side result, we obtain that the complexity of the QBE/definability problems for CQs of treewidth k is EXPTIME-complete for each k > 1. The second relaxation is based on the idea of "desynchronizing" direct products, which characterizes QBE/definability for unions of CQs and reduces the complexity to coNP. The combination of these two relaxations yields tractability for QBE and characterizes it in terms of unions of CQs of treewidth at most k. We also study the complexity of these problems for conjunctive regular path queries over graph databases, showing them to be no more difficult than for CQs