Exploiting Term Hiding to Reduce Run-time Checking Overhead

One of the most attractive features of untyped languages is the flexibility in term creation and manipulation. However, with such power comes the responsibility of ensuring the correctness of these operations. A solution is adding run-time checks to the program via assertions, but this can introduce overheads that are in many cases impractical. While static analysis can greatly reduce such overheads, the gains depend strongly on the quality of the information inferred. Reusable libraries, i.e., library modules that are pre-compiled independently of the client, pose special challenges in this context. We propose a technique which takes advantage of module systems which can hide a selected set of functor symbols to significantly enrich the shape information that can be inferred for reusable libraries, as well as an improved run-time checking approach that leverages the proposed mechanisms to achieve large reductions in overhead, closer to those of static languages, even in the reusable-library context. While the approach is general and system-independent, we present it for concreteness in the context of the Ciao assertion language and combined static/dynamic checking framework. Our method maintains the full expressiveness of the assertion language in this context. In contrast to other approaches it does not introduce the need to switch the language to a (static) type system, which is known to change the semantics in languages like Prolog. We also study the approach experimentally and evaluate the overhead reduction achieved in the run-time checks.Comment: 26 pages, 10 figures, 2 tables; an extension of the paper version accepted to PADL'18 (includes proofs, extra figures and examples omitted due to space reasons

The Evolution of Coordination under Inertia

This paper models the phenomenon of inertia driven by individual strategy switching costs in a stochastic evolutionary context. Kandori, Mailath, and Rob's (1993) model of a finite population of agents repeatedly playing a 2x2 symmetric coordination game is extended to allow for such inertia. Taking noise to the limit, a number of new short- to medium-run equilibria emerge, centred around the mixed-strategy equilibrium. Thus, unusually, an evolutionary model is seen to provide some justification for the controversial concept of mixed-strategy equilibrium. However, Kandori, Mailath, and Rob's long-run selection of the risk-dominant equilibrium continues to hold, both under fixed-rate mutations and under state-dependent mutations driven by stochastic switching costs. The key to this is the satisfaction of Blume's (1999) "skew-symmetry" of the noise process, which is shown to be crucial even under simultaneous strategy revisions. In fact, the presence of the new short-run equilibria can under certain conditions serve to reduce the expected waiting time before the risk-dominant equilibrium is reached - an instance of Ellison's (2000) idea that evolution is more rapid when it can proceed via a series of small "steps" between extremes. This suggests inertia to be a surprisingly efficient phenomenon, and also serves to moderate the force of the Ellison (1993) critique of excessively long transition times in models with vanishing noise.

Short-run dynamics and long-run effects of demographic change on public debt and the budget

The German population is aging. Since fewer children are born and simultaneously life expectancy rises, demographic changes will lead to a double aging process. The paper analyzes the effects of demographic changes on national debt and the public budget by applying a cointegration analysis to global budget variables. Our procedure which covers the period between 1950 and 1990 completes prevailing projections, emphasizing that low vital rates are not the basic problem but the long-run trend of decreasing fertility and mortality rates. The estimation results of several error- correction models show that in the long-run an increase in the old age dependency ratio, and a decrease in the reproduction rate will lead to higher public expenditures. As regards public revenue, the results are ambivalent. The change in the age structure results in higher tax revenue, whereas the decline of population has the opposite effect. Furthermore, we find empirical evidence that aging increases the debt ratio. This development counters current efforts to reduce the public debt share of production potential and the tax load ratio. As a consequence, more action is needed to improve Germanys competiveness as a business location. Compared to these long-run effects, the short-run dynamics is only of minor importance. Significant parameter estimates can be found mainly in the model for the social security contribution rate. --

Exploiting semantic commutativity in hardware speculation

Hardware speculative execution schemes such as hardware transactional memory (HTM) enjoy low run-time overheads but suffer from limited concurrency because they rely on reads and writes to detect conflicts. By contrast, software speculation schemes can exploit semantic knowledge of concurrent operations to reduce conflicts. In particular, they often exploit that many operations on shared data, like insertions into sets, are semantically commutative: they produce semantically equivalent results when reordered. However, software techniques often incur unacceptable run-time overheads. To solve this dichotomy, we present COMMTM, an HTM that exploits semantic commutativity. CommTM extends the coherence protocol and conflict detection scheme to support user-defined commutative operations. Multiple cores can perform commutative operations to the same data concurrently and without conflicts. CommTM preserves transactional guarantees and can be applied to arbitrary HTMs. CommTM scales on many operations that serialize in conventional HTMs, like set insertions, reference counting, and top-K insertions, and retains the low overhead of HTMs. As a result, at 128 cores, CommTM outperforms a conventional eager-lazy HTM by up to 3.4 χ and reduces or eliminates aborts.National Science Foundation (U.S.) (Grant CAREER-1452994

Monetary Policy and Real Stabilization

Monetary policy can achieve average inflation equal to a given inflation target and, at best, a good compromise between inflation variability and output-gap variability. Monetary policy cannot completely stabilize either inflation or the output gap. Increased credibility in the form of inflation expectations anchored on the inflation target will reduce the variability of inflation and the output gap. Central banks can improve transparency and accountability by specifying not only an inflation target but also the dislike of output-gap variability relative to inflation variability. Central banks can best achieve both the long-run inflation target and the best compromise between inflation and output-gap stability by engaging in forecast targeting,' where the bank selects the feasible combination of inflation and output-gap projections that minimize the loss function and the corresponding instrument-rate plan and sets the instrument-rate accordingly. Forecast targeting implies that the instrument responds to all information that significantly affects the projections of inflation and the output gap. Therefore it cannot be expressed in terms of a simple instrument rule, like a Taylor rule. The objective of financial stability, including a well-functioning payment system, can conveniently be considered as a restriction on monetary policy that does not bind in normal times, but does bind in times of financial crises. By producing and publishing Financial Stability Reports with indicators of financial stability, the central bank can monitor the degree of financial stability and issue warnings to concerned agents and authorities in due time and this way avoid deteriorating financial stability. Forecast targeting implies that asset-price developments and potential asset-price bubbles are taken into account and responded to the extent that they are deemed to affect the projections of the target variables, inflation and the output gap. In most cases, it will be difficult to make precise judgments, though, especially to identify bubbles with reasonable certainty. The zero bound, liquidity traps and risks of deflation are serious concerns for a monetary policy aimed at low inflation. Forecast targeting with a symmetric positive inflation target keeps the risk of the zero bound, liquidity traps and deflation small. Prudent central banks may want to prepare in advance contingency plans for situations when a series of bad shocks substantially increases the risk

Reduction of co-simulation runtime through parallel processing

During the design phase of modern digital and mixed signal devices, simulations are run to determine the fitness of the proposed design. Some of these simulations can take large amounts of time, thus slowing down the time to manufacture of the system prototype. One of the typical simulations that is done is an integration simulation that simulates the hardware and software at the same time. Most simulators used in this task are monolithic simulators. Some simulators do have the ability to have external libraries and simulators interface with it, but the setup can be a tedious task. This thesis proposes, implements and evaluates a distributed simulator called PDQScS, that allows for speed up of the simulation to reduce this bottleneck in the design cycle without the tedious separation and linking by the user. Using multiple processes and SMP machines a simulation run time reduction was found

Allocating Payroll Tax Revenue to Personal Retirement Accounts to Maintain Social Security Benefits and the Payroll Tax Rate

In an earlier paper we analyzed a method of combining traditional tax financed pay-as-you-go Social Security benefits with annuities financed by Personal Retirement Accounts. We showed that such a combination could maintain the level of retirement income projected in current Social Security law while avoiding a future increase in the payroll tax rate. The current paper extends the earlier analysis in four ways: (1) We now specify that the funds deposited in the Personal Retirement Accounts come from allocating 2 percent of the 12.4 percent payroll tax instead of being additional funds provided from outside the system. (2) We discuss the effects of the uncertain return on investment based annuities. (3) We provide estimates of the cost of permitting bequests if individuals die either before retirement or during the first twenty years after retirement. (4) We update the statistical basis for our estimates to be consistent with the 2000 Social Security Trustees Report. Our analysis shows that a program of Personal Retirement Accounts funded by allocating 2 percent of the 12.4 percent payroll tax collections can maintain the retirement income projected in current law while avoiding any increase in the 12.4 percent payroll tax. The combination of the higher return on the assets in the Personal Retirement Accounts and the use of the additional corporate profits taxes that result from the increased national saving in Personal Retirement Accounts is sufficient to maintain the solvency of the Social Security Trust Fund even though the tax payments to the fund are reduced from 12.4 percent of taxable payroll to 10.4 percent of taxable payroll. Although there is a period of years when the Trust Fund must borrow, it is able to repay this borrowing with interest out of future tax collections. In the long run, the Trust Fund becomes very large, implying that it would be possible to reduce the payroll tax further or to increase retirement incomes above the levels projected in current law.

Eying the Body: The Impact of Classical Rules for Demeanor Credibility, Bias, and the Need to Blind Legal Decision Makers

This Article focuses on law students and attorneys, not parties, witnesses, experts, and others. Part I briefly provides background: the pivotal role of classical rhetoric in western education, including the United States, the dispositive position of demeanor credibility in oral trial, and the persistent doubts about its reliability—doubts turned into certainty over two decades of research. Part II compares modern and ancient manuals to explain the rules of elite demeanor and its ideological claim to truth. Part III compares ancient and modern understanding of popular delivery; that is, choices in non-verbal communication that run counter to the elite rules and demonstrate affiliation with non-elite groups as grounds for credibility. Part IV shows how elite rules are enforced in law schools and courts, limiting how advocates can speak and, thus, what can be communicated. Part V discusses the role of an assumed natural, common, bodily language in erasing the problem of actual differences and justifying the paradoxical claim that a jury can be manipulated by highly trained professionals, yet ferret out lies. Part VI discusses benefits of the common adoption of elite demeanor and suggests improved instruction at laws schools and screening decision makers in litigation to reduce the cost