Questions tagged [abstract-algebra]

For questions about monoids, groups, rings, modules, fields, vector spaces, algebras over fields, various types of lattices, and other such algebraic objects. Associate with related tags like [group-theory], [ring-theory], [modules], etc. as necessary to clarify which topic of abstract algebra is most related to your question and help other users when searching.

Abstract algebra is the study of algebraic objects, i.e. sets endowed with one or more operations on the elements of those sets. In particular, the study of abstract algebra considers the algebraic structures and properties of which such operations induce. It can be considered as the generalization of the study of the algebraic structure of the integers and real numbers (arithmetic), or the study of matrices and vector spaces (linear algebra).

Some algebraic objects are monoids, groups, rings, fields, vector spaces, modules, algebras, and categories, among many other less prominent objects.

Examples

  1. The set of non-negative integers $\mathbb{N} = \{0,1,2,3,\dotsc\}$ is a monoid under the operation $+$.

  2. The integers $\mathbb{Z} = \{\dotsc,-1,0,1,\dotsc\}$ under the binary operation of $+$ form a group.

  3. Furthermore, $\mathbb{Z}$ has the structure of a ring when you consider it as being equipped with both addition and multiplication.

  4. The real numbers $\mathbb{R}$ with their usual addition and multiplication form a field.

  5. The set of $n\times n$ matrices with entries in $\mathbb{R}$ with matrix addition and multiplication form a ring.

  6. The set of $1\times n$ vectors over the real numbers, with vector addition, and multiplication by elements of the $n\times n$ real matrices on the right are an example of a module for the ring of matrices.

In addition to studying the objects themselves, abstract algebra considers homomorphisms between the objects and various constructions and tools, which are useful for studying the objects.

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Is this Cayley Diagram contradictory?

I was asked to construct a Cayley table for this Cayley diagram and it occurred to me that it will be impossible. My reasoning is that at first glance this appears to be the group $D_4$. It has to be, since it has only two generators. But now, the…
DLV
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If rings $\mathbb Z^m$ and $\mathbb Z^n$ are isomorphic then $m=n$

It is given that the rings $\mathbb Z^m$ and $\mathbb Z^n$ are isomorphic. Show that $m=n$. My try: I want to show that $m\leq n$ and $n\leq m$ . Suppose $m\leq n$.Let $\phi:\mathbb Z^m\to \mathbb Z^n$ be the given isomorphism.Then since…
Learnmore
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Let $G$ be a compact group. If $\{a^n\}_{n \in \mathbb{Z}}$ is dense in $G$, then $G$ is abelian.

It was used in the middle of a theorem's proof and I am not sure how to prove this fact.
B. Rivas
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proving that the symmetric group $S_x$ is not finitely generated where $x$ is infinite

it seems pretty trivial, but I have trouble of showing it. I also wonder of good approach of proving that a group is not finitely generated.
d_e
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Dummit & Foote's Abstract Algebra, 3rd Edition, Exercise 0.1.7

I feel awkward about my reasoning. Is it sound? Let $f:A\to B$ be a surjective map of sets. Prove that the relation $$a\sim b\quad\text{if and only if}\quad f(a)=f(b)$$ is an equivalence relation whose equivalence classes are the fibers of …
wjmolina
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Determining the cardinality of $SL_2 (F_3) $

I have been trying to determine the order of $SL_2 (F_3) $. My books says the answer is 24. But the answer that I am getting is 30. My method: Case 1: Assume that $a_{11} $ is nonzero. Then whatever be the values of the other elements, the value…
user67803
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Problem 1.3 in Martin Issacs' Algebra: A Graduate Course

Let $G$ be any group, let $r_x,l_x: G \to G$ defined by $r_x(g)=gx$, and $l_x(g)=xg$. Let $R=\{r_x:x \in G\}$ and $L=\{l_x:x \in G\}$. Show that $$L=\{f \in \mathrm{Sym}(G): \forall r \in R~~~ fr=rf\}$$ I have thought about it for hours, but I…
learner
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Find a prime $p$ such that $f(x)=x^6 - x^3 +1$ factors in to linear factors in $\mathbb{F}_p[x]$

Find a prime $p$ such that $f(x)=x^6 - x^3 +1$ factors in to linear factors in $\mathbb{F}_p[x]$ $\textbf{My attempt:}$ Notice that $f(x)$ is the $18$-th cyclotomic polynomial, $\Phi_{18}(x)$. For a prime, $p$, which does not divide $18$, the roots…
Yuugi
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Galois extension and prime number.

Let $G$ be a finite group with order $n$, i.e., $|G|=n$. Show that there is a prime number $p\geq n$ and a finite Galois extension $L/K$ with $Gal(L/K)\approx G$ and $[K:\mathbb{Q}]=p!/n$. Honestly, I have no idea!
Cgomes
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Question on Groups $G=\langle x,y|x^4=y^4=e,xyxy^{-1}=e\rangle$

Studying for an exam, a review question... Given $G=\langle x,y|x^4=y^4=e,xyxy^{-1}=e\rangle$. Show $|G|\leq16$. For this, I want to consider that $x^3=x^{-1}$ and $y^3=y^{-1}$ based on our assumptions. I am a little lost as to how to put the…
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Direct product vs direct sum of groups

What is the difference between direct sum and direct product between groups $\mathbb{Z}_n$ and $\mathbb{Z}_m$? I that the same? I found in different literature different notation and I'm very confused about that.
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What is an Integral Domain?

Okay, so almost 3 months into my abstract algebra, we just started rings. I have a few questions. A "trivial ring" is a ring with only one element. So $R={0}$ is a trivial ring. Understandable. Then a definition states: Let $R$ be a ring. If there…
Tyler Hilton
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What Is An Endomorphism Monoid?

I know why an object G gives you a group when you take all its automorphisms. But how does an object G give you a monoid when you take all its endomorphisms? What does it mean to compose two endomorphisms?
John Smith
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Prove that $Q_F$ is not a division ring.

Let F be a finite field of characteristic $p \in \{2, 3, 5\}$. Consider the quaternionic ring, $Q_F = \{a_1 + a_ii + a_j j + a_kk|a_1, a_i, a_j, a_k \in F\}$. Prove that $Q_F$ is not a division ring. I am not sure what I need to show that $Q_F$…
Simple
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Prove that $a^{m}a^{n}=a^{m+n}$ where $m < 0$ and $n > 0$

Prof. Pinter's "A Book of Abstract Algebra" presents this exercise: Let $G$ be a group and $a\in G$ Prove that $a^{m}a^{n}=a^{m+n}$ where $m < 0$ and $n > 0$ To prove $a^{m}a^{n}=a^{m+n}$ where $m < 0$ and $n > 0$, I simply wrote…