/ Satoshi Okawa / Professor
/ Mohamed Hamada / Assistant Professor
The research and education activities in this laboratory focus on the theoretical and practical aspects related to language processing and language processing systems. In paticular, our work covers the following areas.
The research in this laboratory is devided into two parts:
The first part consists of the work that follows the research in the above areas. One of the most important goal of it is to provide the foundations for the education of language processing systems, programing languages, formal language theory.
The second part is the creative study in some specific areas ralated to language processing systems. The research activities of this part are based on the free work of each faculty member. Currently, we are working on
The recent parallel/distributed computation envirnment requires the development of a new language model and its processing model/system for such envirnment. Most programming languages and its processing systems for parallel/distributed systems have been developped based on the traditional computer systems. This development has some advantages and disadvantages. Therefore, the members of this laboratory consider that to design new languages and language processing system is the key work for the next development of the computer society and that it is one of the most important subjects for this laboratory tp study for establishing such models and implementing as real systems for evaluation.
The education on the subjects related tp languages and language processing systems is also the important mission of this laboratory. The courses given by the members of this laboratory include Discrete Systems, Automata and Languges, Language Processing Systems, Mathematical Logics, and SCCP, and Automata and Languages and Compilers, Adavanced Automata and Languages in the Graduate school.
Refereed Journal Papers
In this paper, we attempt to characterize the class of recursively enumerable languages with much smaller language classes than that of linear languages. Language classes, $ (i,j)\,\mathcal{LL} $ and $ (i,j)\,\mathcal{ML} $, of $ (i,j) $ linear languages and $ (i,j) $ minimal linear languages are defined by posing restrictions on the form of production rules and the number of nonterminals. Then the homomorphic characterizations of the class of recursively enumerable languages are obtained using these classes and a class, $ \mathcal{ML} $, of minimal linear languages. That is, for any recursively enumerable language $ L $ over $ \Sigma $, an alphabet $ \Delta $, a homomorphism $ h :\Delta^* \rightarrow \Sigma^* $ and two languages $ L_1 $ and $ L_2 $ over $ \Delta $ in some classes mentioned above can be found such that $ L = h(L_1 \cap L_2) $. The membership relations of $ L_1 $ and $ L_2 $ of the main results are as follows:
For posing restrictions on the forms of production rules, the following result is obtained.
This result is the best one and can not be improved using $ (i,j)\,\mathcal{LL} $. However, with posing more restriction on $ L_2 $, this result can be improved and the follwing statement is obtained.
For posing restrictions on the numbers of nonterminals, the follwing result is obtained.
Refereed Proceeding Papers
Unrefereed Papers
In this papper, we study the portfolio selection problem in the context of online computation and competitive analysis. Instead of the stochastic parameters and the correlations used in the field of finace, we use a graph-based method to describe the correlations. We propose the online portfolio selection algorithm investing to the diversified portfolio. Then, we seek its competitive ratio against a specified type of adversary, and finally show the optimality of the algorithm against this type of adversary. No. 1205, pp. 183--187.