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.

85022 questions
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Use of the '*' symbol

I am looking at the definition of a 'Euclidean domain', on p.51 of the book 'Polynomial Algorithms in Computer Algebra', by F. Winkler. The definition states :- "A Euclidean domain (ED) D is an integral domain together with a degree function…
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Determining the degree of a field extension.

Let $E$ be a field extension of the field $F$. Let $a,b \in E$ and suppose that the minimal polynomial of $a$ over $F$ has degree m, the minimal polynomial of $b$ over $F$ has degree n and that gcd($m,n$)$=1$. Show that $[F(a,b):F]=m\cdot n$. Here's…
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Describe the ker and image of $\phi$

This is an exercise in Artin's Algebra (10.3.11) $\phi :\mathbb{C}[x,y] \rightarrow \mathbb{C}[t]$ is defined by $\phi(x)=t^2$ and $\phi(y)=t^3$ Prove the $\operatorname{Ker} \phi =$ the principal ideal generated by $y^2-x^3$ and describe the…
user9352
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Conditions of being a subgroup

Let $m\mathbb{Z}$ and $n\mathbb{Z}$ be subgroups of $(\mathbb{Z}, +)$. What condition on $m$ and $n$ is equivalent to $m\mathbb{Z}\subseteq n\mathbb{Z}$? What condition on $m$ and $n$ is equivalent to $m\mathbb{Z}\cup n\mathbb{Z}$ being a subgroup…
Lily
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Polynomial relation between two algebraic numbers $p$ and $q$ implies $\mathbb{Q}[q]=\mathbb{Q}[p]$

Let $\mathbb{Q}[a]=\{r \in \mathbb{R}|r \text{ is algebraic over }\mathbb{Q}(a)\}$, and $f(x)$ be a polynomial with rational coefficients such that $f(p)=q$. Thanks to the answers to my question here is now clear to me that $p$ being algebraic…
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Given a field extension $E/k$ why do the norm and trace functions of $E/k$ take values in $k$

I don't quite follow one piece of argument Lang uses about the norm and trace functions. Given a finite field extension $E/k$, he defines the norm of $E/k$ s.t. $N(a)=\Pi_{i=1}^{r} \sigma_i(a^{p^u})$ where $r$ is the degree of separability and $p^u$…
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$\mathbb Q(\sqrt2 + \sqrt3)$ is what set?

I thought $$\mathbb Q(\sqrt2 + \sqrt3) = \left\{a + b\left(\sqrt2+\sqrt3\right) | a,b \in \mathbb Q\right\}$$ I appears I am mistaken. But what set is it?
Aranka
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Fraction field of ring of even polynomials

This might be a dumb question, but I just realized that the field of rational functions $k(x)$ has a subfield consisting of rational functions which can be expressed as fractions of two even polynomials. It came to me when I was thinking about…
Gyujin Oh
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$R[X]/(X)$ is isomorphic to $R$

Let $I$ be a proper ideal of $R$. Prove that $R[X]/(X)$ is isomorphic to $R$. I have no idea how to do this.
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If a subgroup $S$ of $G$ is Abelian (the subgroup, not the entire group!) then is $S$ a normal subgroup?

I saw a glimpse of similarity in their definitions and I thought I'd try to prove or disprove it. I have a feeling that it is true but my attempts to form a proof (that given an Abelian subgroup, that group is a normal subgroup) by using $x\in S$…
Alec Teal
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Exhibiting elements of quotient group and proving isomorphism

This is problem 21 in chapter 3, section 1 of Dummit and Foote. I'm having a lot of trouble with it, so I was hoping anyone would help me out. There are two particular parts I'm struggling with: Let $G=\langle x,y \mid x^4=1=y^4, yx=xy\rangle$ and…
mathmath8128
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Splitting field of $f(x)=x^2+1$ over $F={\bf Z}_2$

Note that $f(x)=x^2+1=(x+1)^2$ has distinct two roots $1,\ i$ so that it is separable polynomial. Hence spliting field is $K={\bf Z}_2(i)=\{ 0,\ 1,\ i\}$ Over $K$, $f(x)$ has factorization $(x-1)(x-i)=x^2+x+ix+1\neq f(x)$ Why does such phenomenon…
HK Lee
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A question on advanced algebra

Let be $\mathbb{R^*}$ and $\mathbb{C^*}$ the multiplicative groups of non-zero real numbers and non-zero complex numbers respectively. Is $\operatorname{Hom}(\mathbb{Z_6},\mathbb{R^*}\oplus\mathbb{C^*})\cong\mathbb{Z_6}\oplus \mathbb{Z_2}? $ Why?
user
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Help understanding how to determine a quotient group

I would like some help in how to determine a quotient group, given two groups. An example: The group $(\mathbb{E},+) $ in $(\mathbb{Z} , +)$. I know the set of the quotient group is all left cosets of $( \mathbb{Z} , + )$ right? So the operation in…
user3200098
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Coset representation ; $\{ Hg_i \} = \{ Hg_i^{-1} \}$

This is my simple curiosity If $H$ is normal in $G$ then $H\setminus G$ is a group : $$ Ha \cdot Hb = H ab $$ But if $H$ is not normal then the coset space $H\setminus G$ is not a group, but we guess that there exists a some property which can be…
HK Lee
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