Deterministic finite automata (DFA) (have odd length or end with aaa)












4












$begingroup$


Is my attempt is true or where am I wrong?



DFA : The set of strings over ${a, b} $ that have odd length or end with $aaa$.



My attempt










share|cite|improve this question











$endgroup$












  • $begingroup$
    Did you try finding a smaller automaton?
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:29










  • $begingroup$
    @k.stm Yes, I tried but I couldn't find.Is this true?
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:30










  • $begingroup$
    Haven’t checked it. Actually, you probably do need eight states. Have you tried organizing them? Can you tell us what each of the states $1$, …, $8$ describe? (Oh, you have nine states – I think you can toss one.)
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:33












  • $begingroup$
    @k.stm there are 8 states.It is hard to describe what each of states describe.
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:41










  • $begingroup$
    It looks correct to me, but the best thing to do is to run it in your computer
    $endgroup$
    – 3SAT
    Mar 24 '16 at 20:58
















4












$begingroup$


Is my attempt is true or where am I wrong?



DFA : The set of strings over ${a, b} $ that have odd length or end with $aaa$.



My attempt










share|cite|improve this question











$endgroup$












  • $begingroup$
    Did you try finding a smaller automaton?
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:29










  • $begingroup$
    @k.stm Yes, I tried but I couldn't find.Is this true?
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:30










  • $begingroup$
    Haven’t checked it. Actually, you probably do need eight states. Have you tried organizing them? Can you tell us what each of the states $1$, …, $8$ describe? (Oh, you have nine states – I think you can toss one.)
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:33












  • $begingroup$
    @k.stm there are 8 states.It is hard to describe what each of states describe.
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:41










  • $begingroup$
    It looks correct to me, but the best thing to do is to run it in your computer
    $endgroup$
    – 3SAT
    Mar 24 '16 at 20:58














4












4








4





$begingroup$


Is my attempt is true or where am I wrong?



DFA : The set of strings over ${a, b} $ that have odd length or end with $aaa$.



My attempt










share|cite|improve this question











$endgroup$




Is my attempt is true or where am I wrong?



DFA : The set of strings over ${a, b} $ that have odd length or end with $aaa$.



My attempt







automata finite-automata






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 24 '16 at 21:01









3SAT

6,34121234




6,34121234










asked Mar 24 '16 at 20:23









zxccxzzxccxz

415




415












  • $begingroup$
    Did you try finding a smaller automaton?
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:29










  • $begingroup$
    @k.stm Yes, I tried but I couldn't find.Is this true?
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:30










  • $begingroup$
    Haven’t checked it. Actually, you probably do need eight states. Have you tried organizing them? Can you tell us what each of the states $1$, …, $8$ describe? (Oh, you have nine states – I think you can toss one.)
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:33












  • $begingroup$
    @k.stm there are 8 states.It is hard to describe what each of states describe.
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:41










  • $begingroup$
    It looks correct to me, but the best thing to do is to run it in your computer
    $endgroup$
    – 3SAT
    Mar 24 '16 at 20:58


















  • $begingroup$
    Did you try finding a smaller automaton?
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:29










  • $begingroup$
    @k.stm Yes, I tried but I couldn't find.Is this true?
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:30










  • $begingroup$
    Haven’t checked it. Actually, you probably do need eight states. Have you tried organizing them? Can you tell us what each of the states $1$, …, $8$ describe? (Oh, you have nine states – I think you can toss one.)
    $endgroup$
    – k.stm
    Mar 24 '16 at 20:33












  • $begingroup$
    @k.stm there are 8 states.It is hard to describe what each of states describe.
    $endgroup$
    – zxccxz
    Mar 24 '16 at 20:41










  • $begingroup$
    It looks correct to me, but the best thing to do is to run it in your computer
    $endgroup$
    – 3SAT
    Mar 24 '16 at 20:58
















$begingroup$
Did you try finding a smaller automaton?
$endgroup$
– k.stm
Mar 24 '16 at 20:29




$begingroup$
Did you try finding a smaller automaton?
$endgroup$
– k.stm
Mar 24 '16 at 20:29












$begingroup$
@k.stm Yes, I tried but I couldn't find.Is this true?
$endgroup$
– zxccxz
Mar 24 '16 at 20:30




$begingroup$
@k.stm Yes, I tried but I couldn't find.Is this true?
$endgroup$
– zxccxz
Mar 24 '16 at 20:30












$begingroup$
Haven’t checked it. Actually, you probably do need eight states. Have you tried organizing them? Can you tell us what each of the states $1$, …, $8$ describe? (Oh, you have nine states – I think you can toss one.)
$endgroup$
– k.stm
Mar 24 '16 at 20:33






$begingroup$
Haven’t checked it. Actually, you probably do need eight states. Have you tried organizing them? Can you tell us what each of the states $1$, …, $8$ describe? (Oh, you have nine states – I think you can toss one.)
$endgroup$
– k.stm
Mar 24 '16 at 20:33














$begingroup$
@k.stm there are 8 states.It is hard to describe what each of states describe.
$endgroup$
– zxccxz
Mar 24 '16 at 20:41




$begingroup$
@k.stm there are 8 states.It is hard to describe what each of states describe.
$endgroup$
– zxccxz
Mar 24 '16 at 20:41












$begingroup$
It looks correct to me, but the best thing to do is to run it in your computer
$endgroup$
– 3SAT
Mar 24 '16 at 20:58




$begingroup$
It looks correct to me, but the best thing to do is to run it in your computer
$endgroup$
– 3SAT
Mar 24 '16 at 20:58










2 Answers
2






active

oldest

votes


















0












$begingroup$

Your automaton is correct but it is not minimal. The minimal automaton only has 5 states. Actually, you can obtain it by minimising your automaton. You will then identify states 2 and 4, states 3 and 5 and states 6 and 8.






share|cite|improve this answer











$endgroup$













  • $begingroup$
    Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:26












  • $begingroup$
    The empty word neither has odd length nor ends in $mathtt {aaa}$.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:33










  • $begingroup$
    There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
    $endgroup$
    – J.-E. Pin
    Mar 25 '16 at 9:36










  • $begingroup$
    No, the initial state is $1$, the other one is a $2$.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:36










  • $begingroup$
    OK, let me correct my answer accordingly.
    $endgroup$
    – J.-E. Pin
    Mar 25 '16 at 9:38



















-1












$begingroup$

Here’s a way to think about the language and the minimal finite automaton describing it:



Whenever you have began typing up a word $u$, there are eight cases you need to consider when trying to finish the word by a suffix $v$ so that the entire word $uv$ will end up in the language. And actually, they split up as $2 × 4$ cases:



How long is $u$?




  • $u$ has an even number of letters.

  • $u$ has an odd number of letters.


How does $u$ end?




  • $u$ does not end in $mathtt a$ (by either being empty or ending in $mathtt b$).

  • $u$ ends in $mathtt a$ (but not in $mathtt {aa}$).

  • $u$ ends in $mathtt {aa}$ (but not in $mathtt {aaa}$).

  • $u$ ends in $mathtt {aaa}$ (or in a suffix with even more $mathtt a$s).


Think about it, that’s all that matters! You should try to check your automaton using that point of view yourself. Try to think of the states in your automaton as encoding that information.



(If you don’t manage to do so or need another pair of eyes, leave a comment.)



This point of view is an insight coming from the Myhill–Nerode theorem.





This answer probably conveys the impression that one needs eight states for any automaton recognizing the given language. That’s because I thought so. But I was wrong. Nevertheless, the procedure given in my answer still works, and one can even see which cases actually behave in the same way and should therefore be considered equivalent.






share|cite|improve this answer











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    2 Answers
    2






    active

    oldest

    votes








    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    0












    $begingroup$

    Your automaton is correct but it is not minimal. The minimal automaton only has 5 states. Actually, you can obtain it by minimising your automaton. You will then identify states 2 and 4, states 3 and 5 and states 6 and 8.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:26












    • $begingroup$
      The empty word neither has odd length nor ends in $mathtt {aaa}$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:33










    • $begingroup$
      There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:36










    • $begingroup$
      No, the initial state is $1$, the other one is a $2$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:36










    • $begingroup$
      OK, let me correct my answer accordingly.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:38
















    0












    $begingroup$

    Your automaton is correct but it is not minimal. The minimal automaton only has 5 states. Actually, you can obtain it by minimising your automaton. You will then identify states 2 and 4, states 3 and 5 and states 6 and 8.






    share|cite|improve this answer











    $endgroup$













    • $begingroup$
      Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:26












    • $begingroup$
      The empty word neither has odd length nor ends in $mathtt {aaa}$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:33










    • $begingroup$
      There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:36










    • $begingroup$
      No, the initial state is $1$, the other one is a $2$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:36










    • $begingroup$
      OK, let me correct my answer accordingly.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:38














    0












    0








    0





    $begingroup$

    Your automaton is correct but it is not minimal. The minimal automaton only has 5 states. Actually, you can obtain it by minimising your automaton. You will then identify states 2 and 4, states 3 and 5 and states 6 and 8.






    share|cite|improve this answer











    $endgroup$



    Your automaton is correct but it is not minimal. The minimal automaton only has 5 states. Actually, you can obtain it by minimising your automaton. You will then identify states 2 and 4, states 3 and 5 and states 6 and 8.







    share|cite|improve this answer














    share|cite|improve this answer



    share|cite|improve this answer








    edited Mar 25 '16 at 9:38

























    answered Mar 25 '16 at 5:01









    J.-E. PinJ.-E. Pin

    18.4k21754




    18.4k21754












    • $begingroup$
      Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:26












    • $begingroup$
      The empty word neither has odd length nor ends in $mathtt {aaa}$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:33










    • $begingroup$
      There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:36










    • $begingroup$
      No, the initial state is $1$, the other one is a $2$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:36










    • $begingroup$
      OK, let me correct my answer accordingly.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:38


















    • $begingroup$
      Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:26












    • $begingroup$
      The empty word neither has odd length nor ends in $mathtt {aaa}$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:33










    • $begingroup$
      There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:36










    • $begingroup$
      No, the initial state is $1$, the other one is a $2$.
      $endgroup$
      – k.stm
      Mar 25 '16 at 9:36










    • $begingroup$
      OK, let me correct my answer accordingly.
      $endgroup$
      – J.-E. Pin
      Mar 25 '16 at 9:38
















    $begingroup$
    Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:26






    $begingroup$
    Of states $1$ and $4$, only one is an accepting state,so identifying them will lead to an inequivalent automaton. You mean $2$ and $4$, I presume.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:26














    $begingroup$
    The empty word neither has odd length nor ends in $mathtt {aaa}$.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:33




    $begingroup$
    The empty word neither has odd length nor ends in $mathtt {aaa}$.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:33












    $begingroup$
    There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
    $endgroup$
    – J.-E. Pin
    Mar 25 '16 at 9:36




    $begingroup$
    There are two states 1 in the picture. Let us call $0$ the initial state to avoid any confusion.
    $endgroup$
    – J.-E. Pin
    Mar 25 '16 at 9:36












    $begingroup$
    No, the initial state is $1$, the other one is a $2$.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:36




    $begingroup$
    No, the initial state is $1$, the other one is a $2$.
    $endgroup$
    – k.stm
    Mar 25 '16 at 9:36












    $begingroup$
    OK, let me correct my answer accordingly.
    $endgroup$
    – J.-E. Pin
    Mar 25 '16 at 9:38




    $begingroup$
    OK, let me correct my answer accordingly.
    $endgroup$
    – J.-E. Pin
    Mar 25 '16 at 9:38











    -1












    $begingroup$

    Here’s a way to think about the language and the minimal finite automaton describing it:



    Whenever you have began typing up a word $u$, there are eight cases you need to consider when trying to finish the word by a suffix $v$ so that the entire word $uv$ will end up in the language. And actually, they split up as $2 × 4$ cases:



    How long is $u$?




    • $u$ has an even number of letters.

    • $u$ has an odd number of letters.


    How does $u$ end?




    • $u$ does not end in $mathtt a$ (by either being empty or ending in $mathtt b$).

    • $u$ ends in $mathtt a$ (but not in $mathtt {aa}$).

    • $u$ ends in $mathtt {aa}$ (but not in $mathtt {aaa}$).

    • $u$ ends in $mathtt {aaa}$ (or in a suffix with even more $mathtt a$s).


    Think about it, that’s all that matters! You should try to check your automaton using that point of view yourself. Try to think of the states in your automaton as encoding that information.



    (If you don’t manage to do so or need another pair of eyes, leave a comment.)



    This point of view is an insight coming from the Myhill–Nerode theorem.





    This answer probably conveys the impression that one needs eight states for any automaton recognizing the given language. That’s because I thought so. But I was wrong. Nevertheless, the procedure given in my answer still works, and one can even see which cases actually behave in the same way and should therefore be considered equivalent.






    share|cite|improve this answer











    $endgroup$


















      -1












      $begingroup$

      Here’s a way to think about the language and the minimal finite automaton describing it:



      Whenever you have began typing up a word $u$, there are eight cases you need to consider when trying to finish the word by a suffix $v$ so that the entire word $uv$ will end up in the language. And actually, they split up as $2 × 4$ cases:



      How long is $u$?




      • $u$ has an even number of letters.

      • $u$ has an odd number of letters.


      How does $u$ end?




      • $u$ does not end in $mathtt a$ (by either being empty or ending in $mathtt b$).

      • $u$ ends in $mathtt a$ (but not in $mathtt {aa}$).

      • $u$ ends in $mathtt {aa}$ (but not in $mathtt {aaa}$).

      • $u$ ends in $mathtt {aaa}$ (or in a suffix with even more $mathtt a$s).


      Think about it, that’s all that matters! You should try to check your automaton using that point of view yourself. Try to think of the states in your automaton as encoding that information.



      (If you don’t manage to do so or need another pair of eyes, leave a comment.)



      This point of view is an insight coming from the Myhill–Nerode theorem.





      This answer probably conveys the impression that one needs eight states for any automaton recognizing the given language. That’s because I thought so. But I was wrong. Nevertheless, the procedure given in my answer still works, and one can even see which cases actually behave in the same way and should therefore be considered equivalent.






      share|cite|improve this answer











      $endgroup$
















        -1












        -1








        -1





        $begingroup$

        Here’s a way to think about the language and the minimal finite automaton describing it:



        Whenever you have began typing up a word $u$, there are eight cases you need to consider when trying to finish the word by a suffix $v$ so that the entire word $uv$ will end up in the language. And actually, they split up as $2 × 4$ cases:



        How long is $u$?




        • $u$ has an even number of letters.

        • $u$ has an odd number of letters.


        How does $u$ end?




        • $u$ does not end in $mathtt a$ (by either being empty or ending in $mathtt b$).

        • $u$ ends in $mathtt a$ (but not in $mathtt {aa}$).

        • $u$ ends in $mathtt {aa}$ (but not in $mathtt {aaa}$).

        • $u$ ends in $mathtt {aaa}$ (or in a suffix with even more $mathtt a$s).


        Think about it, that’s all that matters! You should try to check your automaton using that point of view yourself. Try to think of the states in your automaton as encoding that information.



        (If you don’t manage to do so or need another pair of eyes, leave a comment.)



        This point of view is an insight coming from the Myhill–Nerode theorem.





        This answer probably conveys the impression that one needs eight states for any automaton recognizing the given language. That’s because I thought so. But I was wrong. Nevertheless, the procedure given in my answer still works, and one can even see which cases actually behave in the same way and should therefore be considered equivalent.






        share|cite|improve this answer











        $endgroup$



        Here’s a way to think about the language and the minimal finite automaton describing it:



        Whenever you have began typing up a word $u$, there are eight cases you need to consider when trying to finish the word by a suffix $v$ so that the entire word $uv$ will end up in the language. And actually, they split up as $2 × 4$ cases:



        How long is $u$?




        • $u$ has an even number of letters.

        • $u$ has an odd number of letters.


        How does $u$ end?




        • $u$ does not end in $mathtt a$ (by either being empty or ending in $mathtt b$).

        • $u$ ends in $mathtt a$ (but not in $mathtt {aa}$).

        • $u$ ends in $mathtt {aa}$ (but not in $mathtt {aaa}$).

        • $u$ ends in $mathtt {aaa}$ (or in a suffix with even more $mathtt a$s).


        Think about it, that’s all that matters! You should try to check your automaton using that point of view yourself. Try to think of the states in your automaton as encoding that information.



        (If you don’t manage to do so or need another pair of eyes, leave a comment.)



        This point of view is an insight coming from the Myhill–Nerode theorem.





        This answer probably conveys the impression that one needs eight states for any automaton recognizing the given language. That’s because I thought so. But I was wrong. Nevertheless, the procedure given in my answer still works, and one can even see which cases actually behave in the same way and should therefore be considered equivalent.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Mar 26 '16 at 7:25

























        answered Mar 24 '16 at 21:05









        k.stmk.stm

        10.8k22249




        10.8k22249






























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