NP-Complete Problem: Determine if NFAs A and B Accept Same Language

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In summary, The conversation is about proving the NP-Completeness of a decision problem involving acyclic NFAs. The decision problem asks whether two acyclic NFAs have the same language. It was suggested to use a reduction from SAT to show NP-Hardness, but the speaker is unsure of how to start. The conversation also mentions that each SAT instance has its own language, and that all unsatisfiable instances have an empty language. There is a possibility of solving SAT using a solution to the NFA language problem.
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An NFA (nondeterministic finite automaton) is acyclic if there is no path from a state to itself.

Decision problem: Given two acyclic NFAs A and B, does L(A)=L(B), i.e. does A accept the same language as B.

Show that the above decision problem is NP-Complete.

I am unable to show that it is either NP or NP-hard, but was told that we may use a reduction from SAT to show NP-Hardness. Any help would be appreciated, I have been thinking about this for a while and don't know where to start!
 
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Consider an instance of SAT - you're given a specific boolean formula and are asked whether a variable assignment exists that evaluates to true.

How many such possible assignments are there, for a specific SAT instance? You might say that each SAT instance itself has a language: the language composed of all distinct variable assignments that evaluate to true.

Additionally, under this interpretation, all unsatisfiable SAT instances have the same language - an empty language - given that there are no assignments that evaluate to true.

Do you see a way to solve SAT by using a solution to the problem of determining whether two NFAs have the same language?
 

FAQ: NP-Complete Problem: Determine if NFAs A and B Accept Same Language

What is an NP-Complete problem?

An NP-Complete problem is a type of computational problem that is considered to be one of the most difficult problems to solve. It falls under the complexity class NP, which stands for non-deterministic polynomial time. This means that it is easy to verify a solution to the problem, but it is difficult to find the solution itself.

What does it mean for two NFAs to accept the same language?

Two NFAs (Nondeterministic Finite Automata) accept the same language if they both recognize the same set of strings. This means that given any input string, both NFAs will either accept or reject the string in the same way.

How is the NP-Complete problem of determining if two NFAs accept the same language solved?

The NP-Complete problem of determining if two NFAs accept the same language is solved using an algorithm called the NFA Equivalence Algorithm. This algorithm compares the two NFAs and checks if they have the same structure and if they accept the same strings. If both conditions are met, then the NFAs are considered to accept the same language.

Why is the problem of determining if two NFAs accept the same language considered to be NP-Complete?

This problem is considered to be NP-Complete because it falls under the complexity class NP and it is one of the most difficult problems to solve. It requires non-deterministic polynomial time to solve, meaning that it is difficult to find an efficient solution. Additionally, it is also considered to be complete because it is as difficult as any other NP-Complete problem, meaning that if one NP-Complete problem can be solved efficiently, then all other NP-Complete problems can also be solved efficiently.

What are the applications of solving the NP-Complete problem of determining if two NFAs accept the same language?

The NP-Complete problem of determining if two NFAs accept the same language has many practical applications in fields such as computer science, linguistics, and artificial intelligence. It can be used for language recognition, pattern matching, and optimization problems. Additionally, solving this problem can also help in understanding the complexity of other NP-Complete problems and in developing more efficient algorithms for solving them.

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