Time varying pushdown automata (PDA) are defined and equivalence between two modes of acceptance shown. It is seen that periodically time varying pushdown automata accept exactly the class of context-free languages. Time varying generalized PDA are defined and their equivalence to terminal weighted context free grammars in GNF shown. It is shown that TVGPDA can be simulated by TVPDA. Thus TVPDA give another machine characterization of recursively enumerable sets. © 1988, Taylor & Francis Group, LLC. All rights reserved.

Kamala Krithivasan

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Time varying pushdown automata

International Journal of Computer Mathematics

In this paper, we consider two machine models equivalent in power to Turing machines. Time varying finite automata are defined and it is shown that time varying nondeterministic finite automata are equivalent to time varying deterministic finite automata. But, we find that, when e-moves are introduced, the power is increased to that of Turing machines. Equivalence between time varying regular grammars [6] and time varying nondeterministic finite automata with s-moves is shown. We also consider time varying generalized finite automata and show their equivalence to terminal weighted regular grammars [5], thus proving that time varying generalized finite automata have the same power as Turing machines. © 1986, Taylor & Francis Group, LLC. All rights reserved.

Time Varying Finite Automata

Motivated by the idea of describing parquet deformations using grammars and also of describing an infinite number of terminals starting with only a finite set, this paper defines a terminal weighted grammar, where the terminal generated at any step of a derivation is defined as a function of time. It is seen that terminal weighted regular grammars generate exactly the class of recursively enumerable sets. Terminal weighted matrix grammars are used to describe parquet deformations. The extension of terminal weights to array grammars is also discussed. © 1985.

Computer Vision, Graphics and Image Processing

Terminal weighted grammars and picture description

Motivated by the idea of describing parquet deformations using grammars, we define in this paper a terminal weighted grammar where the terminal generated at any step of a derivation is defined as a function of time. It is seen that terminal weighted regular grammars generate exactly the class of recursively enumerable sets. Terminal weighted matrix grammars are used to describe parquet deformations. The hierarchy of families generated by putting various restrictions on the functions is studied. © 1984, Springer-Verlag.

Journal	International Journal of Computer Mathematics
ISSN	00207160
Open Access	No