The Non-deterministic Push down Automata (NPDAs) are like finite automata (FA), except they also have a stack memory where they can store an arbitrary amount of information.Read/write stack memory works as LIFO: Last In, First OutWhat can we do with a stack?The pop operation reads the top symbol and removes ... Read More

A context-sensitive grammar whose productions are of the formαAβ → αγβWhere α, β ∈ (N ∪ T)*, A ∈ N; γ ∈ (N ∪ T)+ and a rule of the form S → λ is allowed if the start symbol S do not appear on the right hand side of ... Read More

A regular grammar is the one where each production takes one of the following restricted forms −B → ∧, B → w, B → A, B → wA.(Where A, B are non-terminals and w is a non-empty string of terminals.)Restrictions of regular grammarOnly one nonterminal can appear on the right-hand ... Read More

A regular expression is basically a shorthand way of showing how a regular language is built from the base set of regular languages.The symbols are identical which are used to construct the languages, and any given expression that has a language closely associated with it.For each regular expression E, there ... Read More

Construct deterministic finite automata that accepts at most 3 a’s over an alphabet ∑={a, b}.At most 3 a’s means, The string contains 0 to max 3 a’s and any number of b’s.L= {Є, a, aa, aaa, ab, abb, bab, bbabaa, bbabaabbb, …..}Construct DFALet’s construct DFA step by step −Step 1Valid ... Read More

CKY means Cocke-Kasami-Younger. It is one of the earliest recognition and parsing algorithms. The standard version of CKY can only recognize languages defined by context-free grammars in Chomsky Normal Form (CNF).It is also possible to extend the CKY algorithm to handle some grammars which are not in CNF (Hard to ... Read More

ProblemConstruct DFA which accepts a string that contains second symbol is zero and fourth symbol is 1 over an alphabet ∑={0, 1}.SolutionInput − 00110Output is accepted; because in the given string the second symbol is ‘0’ and the fourth symbol is ‘1’.Input − 11001Output − string is not accepted, because the second symbol is ... Read More

A regular expression is basically a shorthand way of showing how a regular language is built from the base set of regular languages.The symbols are identical which are used to construct the languages, and any given expression that has a language closely associated with it.For each regular expression E, there ... Read More

According to the theorem, If L and M are two regular languages, then L ∩ M is also regular language.ExampleConstruct A∩B where A and B is given as follows −The language A ={10, 100, 00, 001, 1010, …..}The language B ={01, 1010, 10, 101, …..}AA = (QA, Σ, δA, qa, ... Read More

ProblemConstruct a deterministic finite automata (DFA) that accepts a language L which has the number of zero’s is of multiple of 3 over an alphabet ∑=”{0, 1}.SolutionIf input is: 000 Output is: string is acceptedBecause here the number of zero’s is multiple of 3.Designing DFAIn order to construct the DFA, ... Read More