A Novel SAT-Based Approach to the Task Graph Cost-Optimal Scheduling Problem

The Task Graph Cost-Optimal Scheduling Problem consists in scheduling a certain number of interdependent tasks onto a set of heterogeneous processors (characterized by idle and running rates per time unit), minimizing the cost of the entire process. This paper provides a novel formulation for this scheduling puzzle, in which an optimal solution is computed through a sequence of Binate Covering Problems, hinged within a Bounded Model Checking paradigm. In this approach, each covering instance, providing a min-cost trace for a given schedule depth, can be solved with several strategies, resorting to Minimum-Cost Satisfiability solvers or Pseudo-Boolean Optimization tools. Unfortunately, all direct resolution methods show very low efficiency and scalability. As a consequence, we introduce a specialized method to solve the same sequence of problems, based on a traditional all-solution SAT solver. This approach follows the "circuit cofactoring" strategy, as it exploits a powerful technique to capture a large set of solutions for any new SAT counter-example. The overall method is completed with a branch-and-bound heuristic which evaluates lower and upper bounds of the schedule length, to reduce the state space that has to be visited. Our results show that the proposed strategy significantly improves the blind binate covering schema, and it outperforms general purpose state-of-the-art tool

When Veblen meets Krugman

We introduce relative concerns in the form of conspicuous consumption in a standard economic geography model a la Krugman. The primary intuition is that conspicuous consumption imposes a negative externality on some agents and generates a centrifugal force. We show that this is not always the case as the relative concern also rises the demand for the sophisticated good, strengthening the standard centripetal market size effect. We show that the resulting force is very sensitive to the topology of the network of "conspicuous" links in each region and on the level of economic integration. For instance, with relatively large shares of income devoted to the consumption of the standard good, we show that when trade is moderately costly and classes of workers are segregated, relative concerns tends to stabilize the symmetric equilibrium; on the other hand, if workers of different classes interact via their relative concerns, conspicuous consumption is a centripetal force generating stable fully or partially agglomerated equilibria. Finally, when the level of integration is high, the intuition holds and even small relative concerns destabilize the full agglomeration equilibrium, which is stable in the Krugman model

Strengthening Model Checking Techniques with Inductive Invariants

This paper describes optimized techniques to efficiently compute and reap benefits from inductive invariants within SAT-based model checking. We address sequential circuit verification, and we consider both equivalences and implications between pairs of nodes in the logic networks. First, we present a very efficient dynamic procedure, based on equivalence classes and incremental SAT, specifically oriented to reduce the set of checked invariants. Then, we show how to effectively integrate the computation of inductive invariants within state-of-the-art SAT-based model checking procedures. Experiments (on more than 600 designs) show the robustness of our approach on verification instances on which stand-alone techniques fai

Apulia agro-biodiversity between rediscovery and conservation: the case of the "Salento km0" network

Green Revolution and the birth of the current global economic system had two opposite, subsequent effects. If, initially, they led to processes of crop homogenization, seasonal adjustment, homogenization of the landscape and markets standardization, they have subsequently pushed local communities towards a recovery of endemic biodiversity at risk of extinction because of such planetary processes, as well as a fundamental element in terms of local development, food security and sovereignty and reduction of environmental impacts. Starting from these instances of recovery and protection, which are increasingly taking place in Apulia, this work will examine both projects created "from above" and initiatives "from below", being the latter the result of a new consciousness that renews social cohesion and gives new value to the territorial milieu. In this regard, the case of the «Salento km0» network will be examined: born in 2011 and now made up of 61 local subjects including producers, restaurateurs, associations, ethical purchasing groups and traditional stores, which represent a key symbol of a territory that resists and a population that has chosen to stay and innovate according to economic, social, cultural and environmental sustainability

Circuit Based Quantification: Back to State Set Manipulation within Unbounded Model Checking

In this paper a non-canonical circuit-based state set representation is used to efficiently perform quantifier elimination. The novelty of this approach lies in adapting equivalence checking and logic synthesis techniques, to the goal of compacting circuit based state set representations resulting from existential quantification. The method can be efficiently combined with other verification approaches such as inductive and SAT-based pre-image verifications