Krogshede_Intersection

    public FA intersection(FA f) throws IllegalArgumentException

    {

        FA FAintersection = new FA(); // We create an Finite Automata

        Set<State> new_accept = new HashSet<State>(); // Here we make a set for states accepting.

 

        if (f.alphabet.equals(this.alphabet)) { // We wanna make sure M1 og M2 use the same alphabet, else we throw an exception

                FAintersection.alphabet = this.alphabet;

        }

 

        else {

                throw new IllegalArgumentException("It's required that the alphabet for M1 and m2 are the same");

        }

 

                ArrayList<StatePair> SP = new ArrayList<StatePair>(); // A statepair, ex : (qo, q1)

                SP = getPairsFromCrossProduct(f);       // q0 x q1 for example

                HashMap<StatePair,State> statePairMap = new HashMap<StatePair,State>(); // New map that takes a StatePair and State to map.

                statePairMap = getStatesfromCrossproduct(SP);

                Map<StateSymbolPair,State> newtransitions = new HashMap<StateSymbolPair,State>();

                Set<State> newStates = new HashSet<State>();

 

        for (StatePair entry : SP) { // In this section we decide which states should be accept-states.

                State s1 = entry.s1;

                State s2 = entry.s2;

                newStates.add(statePairMap.get(entry));

                for(char x : FAintersection.alphabet.symbols) {

                        State d1 = this.delta(s1, x);

                        State d2 = f.delta(s2, x);

                       

                        StatePair res = new StatePair(d1, d2);

                       

                        newtransitions.put((new StateSymbolPair(statePairMap.get(entry), x)), statePairMap.get(res));

                }

 

                if (this.accept.contains(entry.s1) && f.accept.contains(entry.s2)) { // Here we check if both are accept states (1 accept and 1 not_accept will

                                                                                                                                                        //be a not_intersect according to definition)

                        FAintersection.accept.add(statePairMap.get(entry));

                }

 

                new_accept.add(statePairMap.get(entry));

                if (this.initial.equals(entry.s1) && f.initial.equals(entry.s2)) { // Stands for (q0)  

                        FAintersection.initial = statePairMap.get(entry);

                }

        }

        // Here we add all the previous used trasitions, states and accept states to our FAintersection method and return it.

        FAintersection.transitions = newtransitions;

        FAintersection.states = newStates;

        FAintersection.accept = new_accept;

        return FAintersection;

    }