On the Numerical Accuracy of Spreadsheets

This paper discusses the numerical precision of five spreadsheets (Calc, Excel, Gnumeric, NeoOffice and Oleo) running on two hardware platforms (i386 and amd64) and on three operating systems (Windows Vista, Ubuntu Intrepid and Mac OS Leopard). The methodology consists of checking the number of correct significant digits returned by each spreadsheet when computing the sample mean, standard deviation, first-order autocorrelation, F statistic in ANOVA tests, linear and nonlinear regression and distribution functions. A discussion about the algorithms for pseudorandom number generation provided by these platforms is also conducted. We conclude that there is no safe choice among the spreadsheets here assessed: they all fail in nonlinear regression and they are not suited for Monte Carlo experiments.

Water diffusion in rough carbon nanotubes

We use molecular dynamics simulations to study the diffusion of water inside deformed carbon nanotubes with different degrees of deformation at 300 K. We found that the number of hydrogen bonds that water forms depends on nanotube topology, leading to enhancement or suppression of water diffusion. The simulation results reveal that more realistic nanotubes should be considered to understand the confined water diffusion behavior, at least for the narrowest nanotubes, when the interaction between water molecules and carbon atoms is relevant.Comment: 17 pages, 8 figure

EVF: An Extensible and Expressive Visitor Framework for Programming Language Reuse (Artifact)

This artifact is based on EVF, an extensible and expressive Java visitor framework. EVF aims at reducing the effort involved in creation and reuse of programming languages. EVF an annotation processor that automatically generate boilerplate ASTs and AST for a given an Object Algebra interface. This artifact contains source code of the case study on "Types and Programming Languages", illustrating how effective EVF is in modularizing programming languages. There is also a microbenchmark in the artifact that shows that EVF has reasonable performance with respect to traditional visitors

Dependent Merges and First-Class Environments

In most programming languages a (runtime) environment stores all the definitions that are available to programmers. Typically, environments are a meta-level notion, used only conceptually or internally in the implementation of programming languages. Only a few programming languages allow environments to be first-class values, which can be manipulated directly in programs. Although there is some research on calculi with first-class environments for statically typed programming languages, these calculi typically have significant restrictions. In this paper we propose a statically typed calculus, called ?_i, with first-class environments. The main novelty of the ?_i calculus is its support for first-class environments, together with an expressive set of operators that manipulate them. Such operators include: reification of the current environment, environment concatenation, environment restriction, and reflection mechanisms for running computations under a given environment. In ?_i any type can act as a context (i.e. an environment type) and contexts are simply types. Furthermore, because ?_i supports subtyping, there is a natural notion of context subtyping. There are two important ideas in ?_i that generalize and are inspired by existing notions in the literature. The ?_i calculus borrows disjoint intersection types and a merge operator, used in ?_i to model contexts and environments, from the ?_i calculus. However, unlike the merges in ?_i, the merges in ?_i can depend on previous components of a merge. From implicit calculi, the ?_i calculus borrows the notion of a query, which allows type-based lookups on environments. In particular, queries are key to the ability of ?_i to reify the current environment, or some parts of it. We prove the determinism and type soundness of ?_i, and show that ?_i can encode all well-typed ?_i programs

Dependent Merges and First-Class Environments (Artifact)

This artifact contains the mechanical formalization of the calculi associated with the paper Dependent Merges and First-Class Environments. All of the metatheory has been formalized in Coq theorem prover. The paper studies a statically typed calculus, called ?_i, with first-class environments. The main novelty of the ?_i calculus is its support for first-class environments, together with an expressive set of operators that manipulate them