1,394 research outputs found
Postponing Branching Decisions
Solution techniques for Constraint Satisfaction and Optimisation Problems
often make use of backtrack search methods, exploiting variable and value
ordering heuristics. In this paper, we propose and analyse a very simple method
to apply in case the value ordering heuristic produces ties: postponing the
branching decision. To this end, we group together values in a tie, branch on
this sub-domain, and defer the decision among them to lower levels of the
search tree. We show theoretically and experimentally that this simple
modification can dramatically improve the efficiency of the search strategy.
Although in practise similar methods may have been applied already, to our
knowledge, no empirical or theoretical study has been proposed in the
literature to identify when and to what extent this strategy should be used.Comment: 11 pages, 3 figure
Experimental Evaluation of Branching Schemes for the CSP
The search strategy of a CP solver is determined by the variable and value
ordering heuristics it employs and by the branching scheme it follows. Although
the effects of variable and value ordering heuristics on search effort have
been widely studied, the effects of different branching schemes have received
less attention. In this paper we study this effect through an experimental
evaluation that includes standard branching schemes such as 2-way, d-way, and
dichotomic domain splitting, as well as variations of set branching where
branching is performed on sets of values. We also propose and evaluate a
generic approach to set branching where the partition of a domain into sets is
created using the scores assigned to values by a value ordering heuristic, and
a clustering algorithm from machine learning. Experimental results demonstrate
that although exponential differences between branching schemes, as predicted
in theory between 2-way and d-way branching, are not very common, still the
choice of branching scheme can make quite a difference on certain classes of
problems. Set branching methods are very competitive with 2-way branching and
outperform it on some problem classes. A statistical analysis of the results
reveals that our generic clustering-based set branching method is the best
among the methods compared.Comment: To appear in the 3rd workshop on techniques for implementing
constraint programming systems (TRICS workshop at the 16th CP Conference),
St. Andrews, Scotland 201
Lazy Merging: From a Potential of Universes to a Universe of Potentials
Current collaboration workflows force participants to resolve conflicts eagerly, despite having insufficient knowledge and not being aware of their collaborators’ intentions. This is a major reason for bad decisions because it can disregard opinions within the team and cover up disagreements. In our concept of lazy merging we propose to aggregate conflicts as variant potentials. Variant potentials preserve concurrent changes and present the different options to the participants. They can be further merged and edited without restrictions and behave robustly even in complex collaboration scenarios. We use lattice theory to prove important properties and show the correctness and robustness of the collaboration protocol. With lazy merging, conflicts can be resolved deliberately, when all opinions within the team were explored and discussed. This facilitates alignment among team members and prepares them to arrive at the best possible decision that considers the knowledge of the whole team
Truly On-The-Fly LTL Model Checking
We propose a novel algorithm for automata-based LTL model checking that
interleaves the construction of the generalized B\"{u}chi automaton for the
negation of the formula and the emptiness check. Our algorithm first converts
the LTL formula into a linear weak alternating automaton; configurations of the
alternating automaton correspond to the locations of a generalized B\"{u}chi
automaton, and a variant of Tarjan's algorithm is used to decide the existence
of an accepting run of the product of the transition system and the automaton.
Because we avoid an explicit construction of the B\"{u}chi automaton, our
approach can yield significant improvements in runtime and memory, for large
LTL formulas. The algorithm has been implemented within the SPIN model checker,
and we present experimental results for some benchmark examples
HarvOS: Efficient code instrumentation for transiently-powered embedded sensing
We present code instrumentation strategies to allow transiently-powered embedded sensing devices efficiently checkpoint the system's state before energy is exhausted. Our solution, called HarvOS, operates at compile-time with limited developer intervention based on the control-flow graph of a program, while adapting to varying levels of remaining energy and possible program executions at run-time. In addition, the underlying design rationale allows the system to spare the energy-intensive probing of the energy buffer whenever possible. Compared to existing approaches, our evaluation indicates that HarvOS allows transiently-powered devices to complete a given workload with 68% fewer checkpoints, on average. Moreover, our performance in the number of required checkpoints rests only 19% far from that of an "oracle" that represents an ideal solution, yet unfeasible in practice, that knows exactly the last point in time when to checkpoint
Finance and its reform : beyond laissez-faire
That the financial sector should be liberalized was the orthodox view in the mid-1970s, during a pendulum swing toward reliance on the free market. In the early 1980s, the pendulum swung back to the left, based partly on evidence - especially from Latin America - that overly rapid reform had real costs, and partly on an increased appreciation of financial market failure. Blind adherence to free market principles was no longer appropriate. Now a counter-counterrevolution is in sight, with some swing back toward the view that the market makes a mess of it, but the government makes it even worse. The authors agree that market-oriented financial systems appear to do a better job than systems with extensive government involvement, but contend that the assumption that perfect competition will solve all problems in finance - especially in banking - can be dangerous. Information problems, implicit or explicit government guarantees associated with the payments system make banks unique. Governments implicitly recognize banking's uniqueness - few allow just anyone to enter banking - but public pronouncements and observers'recommendations often favor a move to more competition. Perfect competition, however, is optimal under the assumption, among others, of no government guarantee. In fact, most governments differ only in how explicit they are about their deposit insurance schemes. The financial reforms most likely to succeed are those that give banks an incentive to engage in safe and sound banking. When excessive competition is allowed, the charter value of banking diminishes to the point that it is no longer profitable for bankers to behave prudently. A consideration of finance's role, and a look at how reforming economies have fared, suggest also that gradual reform is often to be preferred in this domain. Deregulation of credit markets and interest rates can be counterproductive in unstable macroeconomic conditions and when banks are unsophisticated or have weak balance sheets. And changes in the charter value may evolve only slowly after reform. Faster progress and greater efforts should be made, however, in bank supervision and regulation and in institutional development, including accounting, auditing, legal and judicial reform, and training (of bankers and other finance professionals). In sum, many economies would benefit from less government intervention in financial markets, but the prescription should not be abrupt or total government withdrawal from the financial sector. Rather than intervening heavily in credit allocation decisions, governments should focus on doing what only they can do: providing an enabling environment for the private financial and nonfinancial sectors, and ensuring that financial operations are safe and sound.Environmental Economics&Policies,Banks&Banking Reform,Financial Intermediation,Economic Theory&Research,Financial Crisis Management&Restructuring
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