Space-Optimal Quasi-Gray Codes with Logarithmic Read Complexity

A quasi-Gray code of dimension n and length l over an alphabet Sigma is a sequence of distinct words w_1,w_2,...,w_l from Sigma^n such that any two consecutive words differ in at most c coordinates, for some fixed constant c>0. In this paper we are interested in the read and write complexity of quasi-Gray codes in the bit-probe model, where we measure the number of symbols read and written in order to transform any word w_i into its successor w_{i+1}. We present construction of quasi-Gray codes of dimension n and length 3^n over the ternary alphabet {0,1,2} with worst-case read complexity O(log n) and write complexity 2. This generalizes to arbitrary odd-size alphabets. For the binary alphabet, we present quasi-Gray codes of dimension n and length at least 2^n - 20n with worst-case read complexity 6+log n and write complexity 2. This complements a recent result by Raskin [Raskin \u2717] who shows that any quasi-Gray code over binary alphabet of length 2^n has read complexity Omega(n). Our results significantly improve on previously known constructions and for the odd-size alphabets we break the Omega(n) worst-case barrier for space-optimal (non-redundant) quasi-Gray codes with constant number of writes. We obtain our results via a novel application of algebraic tools together with the principles of catalytic computation [Buhrman et al. \u2714, Ben-Or and Cleve \u2792, Barrington \u2789, Coppersmith and Grossman \u2775]

Barrieren abbauen, Sprache gestalten

Leichte Sprache ist ein zentrales Konzept der barrierefreien Kommunikation. Fachtexte, Informationsbroschüren und andere Texte aus dem täglichen Leben dabei werden in leicht verständliche Texte übersetzt. Die drei Beiträge der vorliegenden Publikation untersuchen verschiedene linguistische Aspekte der Leichten Sprache. Im Speziellen ordnen sie Leichte Sprache als einen Fall von intralingualer Translation ein. Sie untersuchen Komplexität von Leichter Sprache, die Vereinfachungsstrategien, die beim Verfassen von Texten in Leichter Sprache verwendet werden sowie die Strategien, die zur Explizierung in Leichte Sprache Texten verwendet werden.The concept of easy-to-read language is a central one in the area of barrier-free communication. Among other thing, it involves the translation of technical texts, information materials and other texts used in everyday situations into texts that are easy to read. The three contributions in this publication report on investigations of various aspects of easy-to-read language. In particular, they consider easy-to-read language as a special case of intralingual translation. They explore the complexity of easy-to-read language, the simplification strategies that are used in the production of easy-to-read texts, and the strategies that are used for explicitation in such texts

Understanding High School Students\u27 Motivation and Amotivation to Read in and Outside of School: A Phenomenology

The purpose of this phenomenological study was to describe the motivation and amotivation to read of 9th-12th grade adolescents in a large semi-urban high school in southwestern North Carolina. The principal theory guiding this study is Self-Determination Theory (Deci & Ryan, 1985, 1991, 1994, 2000) as it explicates three universal human needs underpinning adolescent motivation to read. This investigation was guided by the following principal research question: How do high school students in southern North Carolina describe their motivation to read? General education high school students (n=12), balanced for gender, ethnicity, race, socioeconomic status, and initial reading motivation, were observed, interviewed in a focus group, and interviewed individually during one semester (15 weeks). Students were enrolled in a semi-urban high school in southwestern North Carolina. Phenomenological reductionism (Schutz, 1970) primarily informed data analysis through bracketing out of personal biases and bracketing in of essential commonalities. Participants offered multiple layers and interpretations of motivations and amotivation to read. Most importantly, students read or do not read primarily through interest, choice, and desire/enjoyment, i.e. autonomy. Students want to read materials that they choose out of personal interest; realizing their own interest is often the first barrier. Further research should be conducted on the following: programs or instruments that facilitate interest-creation, case studies with recorded literacy conversations from homes, and a longitudinal ethnography on personality changes over two to three years and the effects on reading motivation

Percolation scheduling for non-VLIW machines

Percolation Scheduling, a technique for compile-time code parallelization, has proven very successful for exploiting fine-grain irregular parallelism in ordinary programs. Currently, this technology is targeted only to VLIW (Very Long Instruction Word) machines, which have the advantages of 'free' synchronization and communication. Shared memory multi-processors can simulate the execution characteristics of VLIW machines with the use of static barriers. Preliminary results show that Percolation Scheduling can be used with good results on this type of architecture by increasing the granularity from operation level to source statement level, removing any redundant synchronization, and providing an efficient implementation of multi-way jumps

Relaxed Operational Semantics of Concurrent Programming Languages

We propose a novel, operational framework to formally describe the semantics of concurrent programs running within the context of a relaxed memory model. Our framework features a "temporary store" where the memory operations issued by the threads are recorded, in program order. A memory model then specifies the conditions under which a pending operation from this sequence is allowed to be globally performed, possibly out of order. The memory model also involves a "write grain," accounting for architectures where a thread may read a write that is not yet globally visible. Our formal model is supported by a software simulator, allowing us to run litmus tests in our semantics.Comment: In Proceedings EXPRESS/SOS 2012, arXiv:1208.244

Clarifying and compiling C/C++ concurrency: from C++11 to POWER

The upcoming C and C++ revised standards add concurrency to the languages, for the first time, in the form of a subtle *relaxed memory model* (the *C++11 model*). This aims to permit compiler optimisation and to accommodate the differing relaxed-memory behaviours of mainstream multiprocessors, combining simple semantics for most code with high-performance *low-level atomics* for concurrency libraries. In this paper, we first establish two simpler but provably equivalent models for C++11, one for the full language and another for the subset without consume operations. Subsetting further to the fragment without low-level atomics, we identify a subtlety arising from atomic initialisation and prove that, under an additional condition, the model is equivalent to sequential consistency for race-free programs