$mathbb{F}_{4096}$,$mathbb{F}_{16}$ and $mathbb{F}_{2}$












0












$begingroup$


I'm stuck at these two questions:



i)
How many distinct elements $a in mathbb{F}_{4096}$ exist, such that $mathbb{F}_{4096}=mathbb{F}_2 left[aright]$



ii)
Find an irreducible $g in mathbb{F}_4 left[xright]$ such that $mathbb{F}_{16}=mathbb{F}_4/(g)$



As for i) I know that the degree of the minimal polynomial of $a$ has to be $12$, since $2$ is prime and $4096=2^{12}$.



As for ii) I'm lost: Does $deg(g)$ equal to $2$? If so, how would I show that $mathbb{F}_4/(g)$ indeed is $mathbb{F}_{16}$? Is $g=x^2+1$ a viable guess?










share|cite|improve this question









$endgroup$

















    0












    $begingroup$


    I'm stuck at these two questions:



    i)
    How many distinct elements $a in mathbb{F}_{4096}$ exist, such that $mathbb{F}_{4096}=mathbb{F}_2 left[aright]$



    ii)
    Find an irreducible $g in mathbb{F}_4 left[xright]$ such that $mathbb{F}_{16}=mathbb{F}_4/(g)$



    As for i) I know that the degree of the minimal polynomial of $a$ has to be $12$, since $2$ is prime and $4096=2^{12}$.



    As for ii) I'm lost: Does $deg(g)$ equal to $2$? If so, how would I show that $mathbb{F}_4/(g)$ indeed is $mathbb{F}_{16}$? Is $g=x^2+1$ a viable guess?










    share|cite|improve this question









    $endgroup$















      0












      0








      0





      $begingroup$


      I'm stuck at these two questions:



      i)
      How many distinct elements $a in mathbb{F}_{4096}$ exist, such that $mathbb{F}_{4096}=mathbb{F}_2 left[aright]$



      ii)
      Find an irreducible $g in mathbb{F}_4 left[xright]$ such that $mathbb{F}_{16}=mathbb{F}_4/(g)$



      As for i) I know that the degree of the minimal polynomial of $a$ has to be $12$, since $2$ is prime and $4096=2^{12}$.



      As for ii) I'm lost: Does $deg(g)$ equal to $2$? If so, how would I show that $mathbb{F}_4/(g)$ indeed is $mathbb{F}_{16}$? Is $g=x^2+1$ a viable guess?










      share|cite|improve this question









      $endgroup$




      I'm stuck at these two questions:



      i)
      How many distinct elements $a in mathbb{F}_{4096}$ exist, such that $mathbb{F}_{4096}=mathbb{F}_2 left[aright]$



      ii)
      Find an irreducible $g in mathbb{F}_4 left[xright]$ such that $mathbb{F}_{16}=mathbb{F}_4/(g)$



      As for i) I know that the degree of the minimal polynomial of $a$ has to be $12$, since $2$ is prime and $4096=2^{12}$.



      As for ii) I'm lost: Does $deg(g)$ equal to $2$? If so, how would I show that $mathbb{F}_4/(g)$ indeed is $mathbb{F}_{16}$? Is $g=x^2+1$ a viable guess?







      finite-fields extension-field






      share|cite|improve this question













      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Feb 3 at 10:33









      C. BrendelC. Brendel

      638




      638






















          2 Answers
          2






          active

          oldest

          votes


















          1












          $begingroup$

          i) Hint: By a bad choice for $a$, you would end up with $Bbb F_{2048}$ or a sub-field thereof



          ii) Yes, we need $deg g=2$. However, $x^2+1$ is not irreducible: $x^2+1=(x+1)(x+1)$. In fact, any $x^2+ax+b$ with $a,binBbb F_2$ will fail to work as it can at most produce a degree 2 extension of $Bbb F_2$, i.e., it can already be factored in $Bbb F_4$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
            $endgroup$
            – C. Brendel
            Feb 3 at 11:06












          • $begingroup$
            Figured it out myself! Thanks!
            $endgroup$
            – C. Brendel
            Feb 3 at 16:04










          • $begingroup$
            Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
            $endgroup$
            – Jyrki Lahtonen
            Feb 4 at 6:35



















          1












          $begingroup$

          Because $12=2^2cdot3$, the field $Bbb{F}_{4096}$ has the following subfields
          $$
          Bbb{F}_2,Bbb{F}_4,Bbb{F}_8,Bbb{F}_{16},Bbb{F}_{64}.
          $$

          The exponents $m$ of $2^m$ here are the proper factors of $12$, namely $1,2,3,4$ and $6$.



          Of the listed subfields $K_1=Bbb{F}_{16}$ and $K_2=Bbb{F}_{64}$ contain the smaller ones. We further observe that $K_1cap K_2=Bbb{F}_4$. This lets us answer your first question:




          $Bbb{F}_2[alpha]=Bbb{F}_{4096}$ unless $alphain K_1cup K_2$. We need to exclude $$|K_1cup K_2|=|K_1|+|K_2|-|K_1cap K_2|=64+16-4=76$$
          elements. Implying that $4096-76=4020$ choices of $alpha$ will work.




          To answer your second question see the bottom quarter of this answer I prepared for referrals. You will find that with
          $Bbb{F}_4={0,1,beta,beta+1=beta^2}$ an irreducible quadratic is $g(x)=x^2+x+beta$. There are a total of six irreducible monic quadratics in $Bbb{F}_4[x]$. Anyone of them can serve in the role of $g(x)$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
            $endgroup$
            – C. Brendel
            Feb 5 at 16:29












          Your Answer








          StackExchange.ready(function() {
          var channelOptions = {
          tags: "".split(" "),
          id: "69"
          };
          initTagRenderer("".split(" "), "".split(" "), channelOptions);

          StackExchange.using("externalEditor", function() {
          // Have to fire editor after snippets, if snippets enabled
          if (StackExchange.settings.snippets.snippetsEnabled) {
          StackExchange.using("snippets", function() {
          createEditor();
          });
          }
          else {
          createEditor();
          }
          });

          function createEditor() {
          StackExchange.prepareEditor({
          heartbeatType: 'answer',
          autoActivateHeartbeat: false,
          convertImagesToLinks: true,
          noModals: true,
          showLowRepImageUploadWarning: true,
          reputationToPostImages: 10,
          bindNavPrevention: true,
          postfix: "",
          imageUploader: {
          brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
          contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
          allowUrls: true
          },
          noCode: true, onDemand: true,
          discardSelector: ".discard-answer"
          ,immediatelyShowMarkdownHelp:true
          });


          }
          });














          draft saved

          draft discarded


















          StackExchange.ready(
          function () {
          StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3098410%2fmathbbf-4096-mathbbf-16-and-mathbbf-2%23new-answer', 'question_page');
          }
          );

          Post as a guest















          Required, but never shown

























          2 Answers
          2






          active

          oldest

          votes








          2 Answers
          2






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          1












          $begingroup$

          i) Hint: By a bad choice for $a$, you would end up with $Bbb F_{2048}$ or a sub-field thereof



          ii) Yes, we need $deg g=2$. However, $x^2+1$ is not irreducible: $x^2+1=(x+1)(x+1)$. In fact, any $x^2+ax+b$ with $a,binBbb F_2$ will fail to work as it can at most produce a degree 2 extension of $Bbb F_2$, i.e., it can already be factored in $Bbb F_4$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
            $endgroup$
            – C. Brendel
            Feb 3 at 11:06












          • $begingroup$
            Figured it out myself! Thanks!
            $endgroup$
            – C. Brendel
            Feb 3 at 16:04










          • $begingroup$
            Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
            $endgroup$
            – Jyrki Lahtonen
            Feb 4 at 6:35
















          1












          $begingroup$

          i) Hint: By a bad choice for $a$, you would end up with $Bbb F_{2048}$ or a sub-field thereof



          ii) Yes, we need $deg g=2$. However, $x^2+1$ is not irreducible: $x^2+1=(x+1)(x+1)$. In fact, any $x^2+ax+b$ with $a,binBbb F_2$ will fail to work as it can at most produce a degree 2 extension of $Bbb F_2$, i.e., it can already be factored in $Bbb F_4$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
            $endgroup$
            – C. Brendel
            Feb 3 at 11:06












          • $begingroup$
            Figured it out myself! Thanks!
            $endgroup$
            – C. Brendel
            Feb 3 at 16:04










          • $begingroup$
            Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
            $endgroup$
            – Jyrki Lahtonen
            Feb 4 at 6:35














          1












          1








          1





          $begingroup$

          i) Hint: By a bad choice for $a$, you would end up with $Bbb F_{2048}$ or a sub-field thereof



          ii) Yes, we need $deg g=2$. However, $x^2+1$ is not irreducible: $x^2+1=(x+1)(x+1)$. In fact, any $x^2+ax+b$ with $a,binBbb F_2$ will fail to work as it can at most produce a degree 2 extension of $Bbb F_2$, i.e., it can already be factored in $Bbb F_4$.






          share|cite|improve this answer









          $endgroup$



          i) Hint: By a bad choice for $a$, you would end up with $Bbb F_{2048}$ or a sub-field thereof



          ii) Yes, we need $deg g=2$. However, $x^2+1$ is not irreducible: $x^2+1=(x+1)(x+1)$. In fact, any $x^2+ax+b$ with $a,binBbb F_2$ will fail to work as it can at most produce a degree 2 extension of $Bbb F_2$, i.e., it can already be factored in $Bbb F_4$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Feb 3 at 10:40









          Hagen von EitzenHagen von Eitzen

          283k23273508




          283k23273508












          • $begingroup$
            If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
            $endgroup$
            – C. Brendel
            Feb 3 at 11:06












          • $begingroup$
            Figured it out myself! Thanks!
            $endgroup$
            – C. Brendel
            Feb 3 at 16:04










          • $begingroup$
            Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
            $endgroup$
            – Jyrki Lahtonen
            Feb 4 at 6:35


















          • $begingroup$
            If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
            $endgroup$
            – C. Brendel
            Feb 3 at 11:06












          • $begingroup$
            Figured it out myself! Thanks!
            $endgroup$
            – C. Brendel
            Feb 3 at 16:04










          • $begingroup$
            Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
            $endgroup$
            – Jyrki Lahtonen
            Feb 4 at 6:35
















          $begingroup$
          If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
          $endgroup$
          – C. Brendel
          Feb 3 at 11:06






          $begingroup$
          If $a$ is in a sub-ring $K$ of $mathbb{F}_{4096}$ isomorphic to $mathbb{F}_{2048}$ does that imply that $mathbb{F}_2 left[aright] cong mathbb{F}_{2048}$ ? If so: Are the elements that satisfy this condition exactly those of $mathbb{F}_{4096} setminus K$ ? Also: I don't see how $2x=0$ in $mathbb{F}_4$. Thank you for your help!
          $endgroup$
          – C. Brendel
          Feb 3 at 11:06














          $begingroup$
          Figured it out myself! Thanks!
          $endgroup$
          – C. Brendel
          Feb 3 at 16:04




          $begingroup$
          Figured it out myself! Thanks!
          $endgroup$
          – C. Brendel
          Feb 3 at 16:04












          $begingroup$
          Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
          $endgroup$
          – Jyrki Lahtonen
          Feb 4 at 6:35




          $begingroup$
          Hmm. $Bbb{F}_{2048}$ intersects trivially with $Bbb{F}_{4096}$.
          $endgroup$
          – Jyrki Lahtonen
          Feb 4 at 6:35











          1












          $begingroup$

          Because $12=2^2cdot3$, the field $Bbb{F}_{4096}$ has the following subfields
          $$
          Bbb{F}_2,Bbb{F}_4,Bbb{F}_8,Bbb{F}_{16},Bbb{F}_{64}.
          $$

          The exponents $m$ of $2^m$ here are the proper factors of $12$, namely $1,2,3,4$ and $6$.



          Of the listed subfields $K_1=Bbb{F}_{16}$ and $K_2=Bbb{F}_{64}$ contain the smaller ones. We further observe that $K_1cap K_2=Bbb{F}_4$. This lets us answer your first question:




          $Bbb{F}_2[alpha]=Bbb{F}_{4096}$ unless $alphain K_1cup K_2$. We need to exclude $$|K_1cup K_2|=|K_1|+|K_2|-|K_1cap K_2|=64+16-4=76$$
          elements. Implying that $4096-76=4020$ choices of $alpha$ will work.




          To answer your second question see the bottom quarter of this answer I prepared for referrals. You will find that with
          $Bbb{F}_4={0,1,beta,beta+1=beta^2}$ an irreducible quadratic is $g(x)=x^2+x+beta$. There are a total of six irreducible monic quadratics in $Bbb{F}_4[x]$. Anyone of them can serve in the role of $g(x)$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
            $endgroup$
            – C. Brendel
            Feb 5 at 16:29
















          1












          $begingroup$

          Because $12=2^2cdot3$, the field $Bbb{F}_{4096}$ has the following subfields
          $$
          Bbb{F}_2,Bbb{F}_4,Bbb{F}_8,Bbb{F}_{16},Bbb{F}_{64}.
          $$

          The exponents $m$ of $2^m$ here are the proper factors of $12$, namely $1,2,3,4$ and $6$.



          Of the listed subfields $K_1=Bbb{F}_{16}$ and $K_2=Bbb{F}_{64}$ contain the smaller ones. We further observe that $K_1cap K_2=Bbb{F}_4$. This lets us answer your first question:




          $Bbb{F}_2[alpha]=Bbb{F}_{4096}$ unless $alphain K_1cup K_2$. We need to exclude $$|K_1cup K_2|=|K_1|+|K_2|-|K_1cap K_2|=64+16-4=76$$
          elements. Implying that $4096-76=4020$ choices of $alpha$ will work.




          To answer your second question see the bottom quarter of this answer I prepared for referrals. You will find that with
          $Bbb{F}_4={0,1,beta,beta+1=beta^2}$ an irreducible quadratic is $g(x)=x^2+x+beta$. There are a total of six irreducible monic quadratics in $Bbb{F}_4[x]$. Anyone of them can serve in the role of $g(x)$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
            $endgroup$
            – C. Brendel
            Feb 5 at 16:29














          1












          1








          1





          $begingroup$

          Because $12=2^2cdot3$, the field $Bbb{F}_{4096}$ has the following subfields
          $$
          Bbb{F}_2,Bbb{F}_4,Bbb{F}_8,Bbb{F}_{16},Bbb{F}_{64}.
          $$

          The exponents $m$ of $2^m$ here are the proper factors of $12$, namely $1,2,3,4$ and $6$.



          Of the listed subfields $K_1=Bbb{F}_{16}$ and $K_2=Bbb{F}_{64}$ contain the smaller ones. We further observe that $K_1cap K_2=Bbb{F}_4$. This lets us answer your first question:




          $Bbb{F}_2[alpha]=Bbb{F}_{4096}$ unless $alphain K_1cup K_2$. We need to exclude $$|K_1cup K_2|=|K_1|+|K_2|-|K_1cap K_2|=64+16-4=76$$
          elements. Implying that $4096-76=4020$ choices of $alpha$ will work.




          To answer your second question see the bottom quarter of this answer I prepared for referrals. You will find that with
          $Bbb{F}_4={0,1,beta,beta+1=beta^2}$ an irreducible quadratic is $g(x)=x^2+x+beta$. There are a total of six irreducible monic quadratics in $Bbb{F}_4[x]$. Anyone of them can serve in the role of $g(x)$.






          share|cite|improve this answer









          $endgroup$



          Because $12=2^2cdot3$, the field $Bbb{F}_{4096}$ has the following subfields
          $$
          Bbb{F}_2,Bbb{F}_4,Bbb{F}_8,Bbb{F}_{16},Bbb{F}_{64}.
          $$

          The exponents $m$ of $2^m$ here are the proper factors of $12$, namely $1,2,3,4$ and $6$.



          Of the listed subfields $K_1=Bbb{F}_{16}$ and $K_2=Bbb{F}_{64}$ contain the smaller ones. We further observe that $K_1cap K_2=Bbb{F}_4$. This lets us answer your first question:




          $Bbb{F}_2[alpha]=Bbb{F}_{4096}$ unless $alphain K_1cup K_2$. We need to exclude $$|K_1cup K_2|=|K_1|+|K_2|-|K_1cap K_2|=64+16-4=76$$
          elements. Implying that $4096-76=4020$ choices of $alpha$ will work.




          To answer your second question see the bottom quarter of this answer I prepared for referrals. You will find that with
          $Bbb{F}_4={0,1,beta,beta+1=beta^2}$ an irreducible quadratic is $g(x)=x^2+x+beta$. There are a total of six irreducible monic quadratics in $Bbb{F}_4[x]$. Anyone of them can serve in the role of $g(x)$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Feb 4 at 6:34









          Jyrki LahtonenJyrki Lahtonen

          110k13172392




          110k13172392












          • $begingroup$
            Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
            $endgroup$
            – C. Brendel
            Feb 5 at 16:29


















          • $begingroup$
            Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
            $endgroup$
            – C. Brendel
            Feb 5 at 16:29
















          $begingroup$
          Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
          $endgroup$
          – C. Brendel
          Feb 5 at 16:29




          $begingroup$
          Oh! Neat! Thanks. Already handed the assignment in... I guess in i) I goofed a little :P as for ii) in the end I just went with multiplying every possible linear factor with another to rule out any reducibles of degree 2 :) Very much appreciated!
          $endgroup$
          – C. Brendel
          Feb 5 at 16:29


















          draft saved

          draft discarded




















































          Thanks for contributing an answer to Mathematics Stack Exchange!


          • Please be sure to answer the question. Provide details and share your research!

          But avoid



          • Asking for help, clarification, or responding to other answers.

          • Making statements based on opinion; back them up with references or personal experience.


          Use MathJax to format equations. MathJax reference.


          To learn more, see our tips on writing great answers.




          draft saved


          draft discarded














          StackExchange.ready(
          function () {
          StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3098410%2fmathbbf-4096-mathbbf-16-and-mathbbf-2%23new-answer', 'question_page');
          }
          );

          Post as a guest















          Required, but never shown





















































          Required, but never shown














          Required, but never shown












          Required, but never shown







          Required, but never shown

































          Required, but never shown














          Required, but never shown












          Required, but never shown







          Required, but never shown







          Popular posts from this blog

          Can a sorcerer learn a 5th-level spell early by creating spell slots using the Font of Magic feature?

          Does disintegrating a polymorphed enemy still kill it after the 2018 errata?

          A Topological Invariant for $pi_3(U(n))$