If $G$ is linear over $mathbb{Z}$ then $operatorname{Aut}(G)$ is linear over $mathbb{Z}$ as well?












3















If $G$ is linear over $mathbb{Z}$ then $operatorname{Aut}(G)$ is linear over
$mathbb{Z}$ as well?




We have $G cong H leq GL(n, mathbb{Z})$ for some $n$ (this is what I mean when I say that $G$ is linear over $mathbb{Z}$)



Then is $operatorname{Aut}(G) cong N leq GL(n^2, mathbb{Z})$?





I need this in context of:




$G$ polycyclic, $Gamma leq operatorname{Aut}(G)$ solvable $implies Gamma$
polycyclic




If the topic assertion is correct then this can proven as:



Every polycyclic group is linear of $mathbb{Z}$, and every solvable linear group of $mathbb{Z}$ is polycyclic.










share|cite|improve this question




















  • 2




    What does " being linear over $;Bbb Z;$" mean, anyway?
    – DonAntonio
    Nov 24 at 15:24








  • 2




    @DonAntonio We're using it as saying that $G$ is isomorphic to a subgroup of $GL(n, mathbb{Z})$ for some $n$
    – Mariah
    Nov 24 at 15:25


















3















If $G$ is linear over $mathbb{Z}$ then $operatorname{Aut}(G)$ is linear over
$mathbb{Z}$ as well?




We have $G cong H leq GL(n, mathbb{Z})$ for some $n$ (this is what I mean when I say that $G$ is linear over $mathbb{Z}$)



Then is $operatorname{Aut}(G) cong N leq GL(n^2, mathbb{Z})$?





I need this in context of:




$G$ polycyclic, $Gamma leq operatorname{Aut}(G)$ solvable $implies Gamma$
polycyclic




If the topic assertion is correct then this can proven as:



Every polycyclic group is linear of $mathbb{Z}$, and every solvable linear group of $mathbb{Z}$ is polycyclic.










share|cite|improve this question




















  • 2




    What does " being linear over $;Bbb Z;$" mean, anyway?
    – DonAntonio
    Nov 24 at 15:24








  • 2




    @DonAntonio We're using it as saying that $G$ is isomorphic to a subgroup of $GL(n, mathbb{Z})$ for some $n$
    – Mariah
    Nov 24 at 15:25
















3












3








3


1






If $G$ is linear over $mathbb{Z}$ then $operatorname{Aut}(G)$ is linear over
$mathbb{Z}$ as well?




We have $G cong H leq GL(n, mathbb{Z})$ for some $n$ (this is what I mean when I say that $G$ is linear over $mathbb{Z}$)



Then is $operatorname{Aut}(G) cong N leq GL(n^2, mathbb{Z})$?





I need this in context of:




$G$ polycyclic, $Gamma leq operatorname{Aut}(G)$ solvable $implies Gamma$
polycyclic




If the topic assertion is correct then this can proven as:



Every polycyclic group is linear of $mathbb{Z}$, and every solvable linear group of $mathbb{Z}$ is polycyclic.










share|cite|improve this question
















If $G$ is linear over $mathbb{Z}$ then $operatorname{Aut}(G)$ is linear over
$mathbb{Z}$ as well?




We have $G cong H leq GL(n, mathbb{Z})$ for some $n$ (this is what I mean when I say that $G$ is linear over $mathbb{Z}$)



Then is $operatorname{Aut}(G) cong N leq GL(n^2, mathbb{Z})$?





I need this in context of:




$G$ polycyclic, $Gamma leq operatorname{Aut}(G)$ solvable $implies Gamma$
polycyclic




If the topic assertion is correct then this can proven as:



Every polycyclic group is linear of $mathbb{Z}$, and every solvable linear group of $mathbb{Z}$ is polycyclic.







abstract-algebra group-theory solvable-groups






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share|cite|improve this question













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share|cite|improve this question








edited Nov 24 at 15:46

























asked Nov 24 at 15:19









Mariah

1,282518




1,282518








  • 2




    What does " being linear over $;Bbb Z;$" mean, anyway?
    – DonAntonio
    Nov 24 at 15:24








  • 2




    @DonAntonio We're using it as saying that $G$ is isomorphic to a subgroup of $GL(n, mathbb{Z})$ for some $n$
    – Mariah
    Nov 24 at 15:25
















  • 2




    What does " being linear over $;Bbb Z;$" mean, anyway?
    – DonAntonio
    Nov 24 at 15:24








  • 2




    @DonAntonio We're using it as saying that $G$ is isomorphic to a subgroup of $GL(n, mathbb{Z})$ for some $n$
    – Mariah
    Nov 24 at 15:25










2




2




What does " being linear over $;Bbb Z;$" mean, anyway?
– DonAntonio
Nov 24 at 15:24






What does " being linear over $;Bbb Z;$" mean, anyway?
– DonAntonio
Nov 24 at 15:24






2




2




@DonAntonio We're using it as saying that $G$ is isomorphic to a subgroup of $GL(n, mathbb{Z})$ for some $n$
– Mariah
Nov 24 at 15:25






@DonAntonio We're using it as saying that $G$ is isomorphic to a subgroup of $GL(n, mathbb{Z})$ for some $n$
– Mariah
Nov 24 at 15:25












1 Answer
1






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oldest

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5














The answer to your question is no, because all free groups $F_n$ of finite rank are linear over ${mathbb Z}$, but it is proved here that ${rm Aut}(F_n)$ is not linear (over any field) for $n ge 3$.



It is proved in Chapter 2 of Dan Segal's book on polycyclic groups that solvable subgroups of ${rm GL}(n,{mathbb Z})$ are polycyclic.






share|cite|improve this answer





















  • would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
    – Mariah
    Nov 25 at 13:47











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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









5














The answer to your question is no, because all free groups $F_n$ of finite rank are linear over ${mathbb Z}$, but it is proved here that ${rm Aut}(F_n)$ is not linear (over any field) for $n ge 3$.



It is proved in Chapter 2 of Dan Segal's book on polycyclic groups that solvable subgroups of ${rm GL}(n,{mathbb Z})$ are polycyclic.






share|cite|improve this answer





















  • would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
    – Mariah
    Nov 25 at 13:47
















5














The answer to your question is no, because all free groups $F_n$ of finite rank are linear over ${mathbb Z}$, but it is proved here that ${rm Aut}(F_n)$ is not linear (over any field) for $n ge 3$.



It is proved in Chapter 2 of Dan Segal's book on polycyclic groups that solvable subgroups of ${rm GL}(n,{mathbb Z})$ are polycyclic.






share|cite|improve this answer





















  • would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
    – Mariah
    Nov 25 at 13:47














5












5








5






The answer to your question is no, because all free groups $F_n$ of finite rank are linear over ${mathbb Z}$, but it is proved here that ${rm Aut}(F_n)$ is not linear (over any field) for $n ge 3$.



It is proved in Chapter 2 of Dan Segal's book on polycyclic groups that solvable subgroups of ${rm GL}(n,{mathbb Z})$ are polycyclic.






share|cite|improve this answer












The answer to your question is no, because all free groups $F_n$ of finite rank are linear over ${mathbb Z}$, but it is proved here that ${rm Aut}(F_n)$ is not linear (over any field) for $n ge 3$.



It is proved in Chapter 2 of Dan Segal's book on polycyclic groups that solvable subgroups of ${rm GL}(n,{mathbb Z})$ are polycyclic.







share|cite|improve this answer












share|cite|improve this answer



share|cite|improve this answer










answered Nov 24 at 15:52









Derek Holt

52.3k53570




52.3k53570












  • would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
    – Mariah
    Nov 25 at 13:47


















  • would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
    – Mariah
    Nov 25 at 13:47
















would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
– Mariah
Nov 25 at 13:47




would you mind checking out my new question; its related to the one here and I will appreciate your guidance there: math.stackexchange.com/questions/3012808/…
– Mariah
Nov 25 at 13:47


















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