A push down automata (PDA) can be formally described as seven tuples(Q, Σ, S, δ, q0, I, F)Where, Q is finite number of statesΣ is input alphabetS is stack symbolΔ is the transition function: QX(ΣU{e})XSXQq0 is the initial state (q0 belongs to Q)I is the initial state top symbolF is ... Read More

L = {ww’ | wcw’, w={0, 1}*} where w’ is the reverse of w.This is the language of all palindromes, both odd and even over the alphabet {0, 1}.For the construction of all length palindromes, let us use the Non-deterministic push down automata (NPDA).To construct the wcw’ we need to ... Read More

DPDA is the short form for the deterministic push down automata (DPDA).ProblemConstruct DPDA for anbncm where m, n>=1SolutionSo, the strings which are generated by the given language are −L={abc, aabbc, aaabbbcc, ….}That is we have to count equal number of a’s, b’s and different number of c’sLet’s count the number ... Read More

ProblemConstruct deterministic push down automata (DPDA) for anbn where n>=1.SolutionSo, the strings which are generated by the given language are as follows −L={ab, aabb, aaabbb, ….}That is we have to count equal number of a’s and b’sThis can be achieved by pushing a's in STACK and then we will pop ... Read More

Let us understand the push down automata (PDA) and the linear bounded automata (LBA) in the theory of computation (TOC).Push-Down AutomataA PDA can be formally described as seven tuples (Q, Σ, S, δ, q0, I, F)Where, Q is finite no of statesΣ is input alphabetS is stack symbolΔ is the ... Read More

The Context sensitive grammar (CSG) is defined as G=(V, Σ, P, S)Where, V: Non terminals or variables.Σ: Input symbols.P: Production rule.P:{αAβ → αγβ, A ϵ V, α ϵ (V∪Σ)*, β ϵ (V∪Σ)*S: Starting symbol.ExampleaS→SAa|aAaA→abcIn context sensitive grammar, there is either left context or right context (αAβ i.e. α is left ... Read More

If the grammar satisfies the following two conditions, then we can say that type of grammar is called as operator precedence grammar.If ε is on its RHS then there exists no production rule.If two non-terminals are adjacent to each other on its RHS then there exists no production rule.Operator Grammars ... Read More

A Context Free Grammar (CFG) is said to be in Greibach Normal Form(GNF), if production rules satisfy one of the following criteria −Only a start symbol can generate ε. For example, if S is the start symbol then S → ε is in GNF.A non-terminal can generate a terminal. For ... Read More

We know that the languages accepted by finite automata (FA) are called regular languages and the languages accepted by push down automata (PDA) are called context free languages (CFG).Closure of CFLs under UnionCFL is the short form for Context Free Language. Here the CFL is as follows −G = (V, ... Read More

Mealy MachineIn a Mealy machine the output symbol depends upon the present input symbol and present state of the machine.In the Mealy machine, the output is represented with each input symbol and each state is separated by /.The Mealy machine can be described by six tuples (Q, q0, Σ, O, ... Read More