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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Showing $\mathbb{C}[U,V,W]/(V^2-UW) \cong \mathbb{C}[X,XY,XY^2].$

Let $\phi$ be the $\mathbb{C}$ algebra homomorphism from $\mathbb{C}[U,V,W] \to \mathbb{C}[X,XY,XY^2]$ that sends $U$ to $X,$ $V$ to $XY$ and $W$ to $XY^2.$ Let $I:= (V^2-UW).$ I am trying to show that $I$ is the kernel of $\phi.$ The hard direction…
Katie Dobbs
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Is the first Weyl algebra strongly $\mathbb{Z}$-graded?

Let $k$ a field of characteristic zero and $A = k\langle x , y\rangle / (xy - yx -1)$ the first Weyl algebra. Let $A$ be given a $\mathbb{Z}$-grading by setting $\deg(x) = 1$ and $\deg(y) = -1$. Is this a strong $\mathbb{Z}$-grading? (i.e. does…
YSB
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[Dummit and Foote : Algebra] 2.1 Subgroups Question 10(b) Some help/hint please

So, the question goes like this "Prove that the intersection of an arbitrary nonempty collection of subgroups of $G$ is again a subgroup of $G$ (do not assume the collection is countable)." At first, I thought of approaching this question with a…
biralol
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Automorphisms of $\mathbb Z_p[x]$

I am trying to find all automorphisms of $\mathbb Z_p[x]$ (polynomials with coefficients from $\mathbb Z_p$ where $p$ is prime). I know that automorphisms of $\mathbb Z[x]$ are $x\to x$ and $x\to -x$, but now when coefficients are in $\mathbb…
stella
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Addition of ideals

Given a ring $R$ and ideals $A,C$ suppose we have $A + B' =A + B = C.$ I was wondering then what can we say about relation between $B$ and $B'$. Clearly, $B$ may not equal $B'$, but can we say something? Does it follow that $B= B' + D$ where $D$ is…
Tom Mosher
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Find all invertible elements of $ \Bbb{Q}[x]/(x^{600}) $.

I know that invertible elements of $\Bbb{Q}[x]$ are constants, so $\Bbb{Q}$. But in $\Bbb{Q}[x]/(x^{600})$, I suppose there are more invertible elements. How to find all of them?
stella
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Consider a set equipped with two idempotent functions that commute.

Consider a set $X$ equipped and two functions $f,g : X \rightarrow X$. Assume $f$ and $g$ commute with each other. Finally, call $x \in X$ a fixed point of $f$ iff $f(x)=x.$ Then we can show that if $x$ is a fixed point of $f$, then so too is…
goblin GONE
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Help with a proof of Sharp's Steps in commutative algebra

I'm trying to understand the following part of this book I couldn't prove that $aR=\Pi_{i=1}^sRp^{t_i}_i$. $\subset$ part: $x\in aR\implies x=ar_1\implies x=up_1^{t_1}...p_s^{t_s}r_1\implies x=(ur_1)p_1^{t_1}...p_s^{t_s}, r_1\in R$, since $R$ is…
user75086
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Is $e$ a zero of power series with rational coefficients?

Since $e$ is a transcendence number, so it is certain that it is not zero of any polynomial with rational coefficients. However, I wonder can we find a power series with rational coefficient such that it is zero evaluated at $e$. If such series…
Ken.Wong
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How do I show that $\text{Sym}^k(V)\oplus\bigwedge^k(V)=V^{\otimes k}$?

I have defined both $\text{Sym}^k(V)$ and $\bigwedge^k(V)$ as quotient space of vector power $V^{\otimes k}$. So how do I understand that $\text{Sym}^k(V)\oplus\bigwedge^k(V)=V^{\otimes k}$, since elements of symmetric and exterior power are…
nakajuice
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Right and left inverse

If $AR=I$ ($R$ is the right inverse) and $LA=I$ (L is the left inverse), how can we show that $L=R$? I am a bit skeptic about the statement but stuck at the moment in terms of showing that $L=R$. Any help would be great!
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Find a subgroup of order $6$ in $U(700).$

Find a subgroup of order $6$ in $U(700).$ My attempt: $U(700)=U(2^2.5^2.7)\simeq U(2^2)\oplus U(5^2)\oplus U(7)\simeq\mathbb Z_2\oplus\mathbb Z_{5^2-5}\oplus\mathbb Z_{7-7^0}\simeq\mathbb Z_2\oplus\mathbb Z_{20}\oplus\mathbb Z_6\\\mathbb…
Sriti Mallick
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can you help me to understand this proposition?

The units of the ring F[x] are polynomials of degree 1. (i.e. nonzero constant polynomials ) I don't understand what this sentence means that. Can you give me proof or an example to understand? thank you in advance.
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Definition of a Group in Abstract Algebra Texts

Why do abstract algebra texts generally define a group something like more-or-less this... Let * denote a binary operation on a set G. For all x, y, z in G x*(y*z)=(x*y)*z There exists an element 1 in G, such that for all x in G, x*1=x For all x in…
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Gauss Lemma for Polynomials and Divisibility in $\mathbb Z$ and $\mathbb Q$.

I am working through Gauss Lemma and various corollaries of it. In the book Algebra of Michael Artin, I have a question to the proof of the following Theorem: Theorem. (a) Let $f,g$ be polynomials in $\mathbb Q[x]$, and let $f_0, g_0$ be the…
StefanH
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