Questions tagged [primary-decomposition]

For questions related to primary decomposition. In mathematics, every ideal can be decomposed as an intersection, called primary decomposition, of finitely many primary ideals (which are related to, but not quite the same as, powers of prime ideals).

In mathematics, the Lasker–Noether theorem states that every Noetherian ring is a Lasker ring, which means that every ideal can be decomposed as an intersection, called primary decomposition, of finitely many primary ideals (which are related to, but not quite the same as, powers of prime ideals).

Let $R$ be a Noetherian commutative ring. An ideal $I$ of $R$ is called primary if it is a proper ideal and for each pair of elements $x$ and $y$ in $R$ such that $xy$ is in $I$, either $x$ or some power of $y$ is in $I$; equivalently, every zero-divisor in the quotient $R/I$ is nilpotent. The radical of a primary ideal $Q$ is a prime ideal and $Q$ is said to be $\mathfrak {p}$-primary for $\displaystyle {\mathfrak {p}}={\sqrt {Q}}$.

For more, check this link.

130 questions
6
votes
1 answer

Exercise 4.19 in Atiyah-MacDonald

I'm unable to prove the last sentence in the hint to Exercise 4.19 in the book by Atiyah and MacDonald. Here is the statement of the exercise (with the notation $\subset$ instead of $\subseteq$ for inclusion): Let $A$ be a ring and $\mathfrak p$ a…
4
votes
2 answers

For which Noetherian local rings, is every associated prime ideal contained in the square of the maximal ideal?

Let $(R,\mathfrak m, k)$ be a Noetherian local ring of depth $>1$. If $a\in R$ is a zero-divisor, i.e. if $ab=0$ for some $0\ne b \in R$, then must it be true that $a\in \mathfrak m^2$? Since the collection of all zero divisors is the union of all…
4
votes
0 answers

Counterexamples to standard assertions on associated primes

I have recently started reading section 6 of Matsumura's "Commutative Ring Theory", and I have noticed that some of the results from Theorems 6.1 through 6.5 make the assumption of Noetherianness of the underlying ring while some others don't. I…
4
votes
1 answer

Intersection of two primary ideals in $\mathbb{Z}[x]$.

Consider $\mathbb{Z}[x]$, and define $I = (x(x^{2}-2),(x^{2}-2)(x^{2}+2))$, $J = (x^{2}-2)\cap(x^{3},2)$. I want to show that $I = J$. Notice that $I\subset J$ is clear since the generators of $I$ are clearly in $J$. The other direction is less…
3
votes
0 answers

Completion of primary ideal is primary

I have the following question. Suppose $(R, \mathfrak{m})$ is a local Noetherian ring, $\mathfrak{a}$ is $\mathfrak{p}$-primary ideal. Is it true that $\hat{\mathfrak{a}}$ is a primary ideal in $\hat{R}$, where $\hat{}$ mean $\mathfrak{m}$-adic…
3
votes
1 answer

Example of a nonzero ideal which is contained in every other non zero ideal.

I am searching for a ring in which $0$ ideal is irreducible but not primary. I have an idea to show that $0$ ideal is irreducible : We have to construct a ring $R$ in such a way that there exist a nontrivial ideal $J$ such that $J \subseteq I$ for…
3
votes
1 answer

Localisation map is zero or injective, then zero ideal is primary.

Question Let $M$ be an $R$ module such that for every multiplicative closed set $S\subset R$, the kernel of natural map $M\to S^{-1}M$ is $(0)$ or $M$. Show that $(0)$ is primary in $M$. Attempt I have the below proof of the above statement when $M$…
3
votes
1 answer

Hoffman and Kunze ,Linear algebra Sec 7.4 exercise 4

Construct a linear operator $T$ with minimal polynomial $ x^2(x-1)^2 $ and characteristic polynomial $x^3(x-1)^4$. Describe the primary decomposition of the vector space under $T$ and find the projections on the primary components. Find a basis in…
2
votes
1 answer

Proving an ideal is primary

I want to prove that a class of ideals are all primary ideals. It may be easier to demonstrate with an example. Let $I=(a^2,ab,ac,b^2,ad+bc,bd+c^2)$. I want to show that $I$ is $P$-primary where $P=(a,b,c)$. Set $R=k[a,b,c,d]$. Macaulay2 has…
2
votes
1 answer

Problem of finding the invariant factors and elementary divisors of a quotient group.

$\mathbf{The \ Problem \ is}:$ Let $G:= \Bbb{Z}_9\times \Bbb{Z}_9\times \Bbb{Z}_9$ and $H:= \langle(6,6,6)\rangle.$ Find the invariant factors and elementary divisors of the quotient group $G/H.$ $\mathbf{My \ Approach}:$ Note,…
2
votes
0 answers

Proving that if $J=\bigcap_{n\geq0}I^n$ then $IJ = J$

I'm having some trouble with the following exercise: Let $R$ be a Noetherian commutative ring, $I$ and ideal and $J=\bigcap_{n\geq0}I^n$. Show that $IJ = J$. (Hint: Assume that $J\not\subseteq IJ$ and consider a primary decomposition of $IJ$. Take…
2
votes
0 answers

Is every subspace can be represented as T-cyclic for some T?

Definition of $T$-cyclic subspace: Let $T$ be an linear operator on $V$. Take $v \in V$. The subspace generated by $\text{span}(\{v,T(v),T^2(v),\cdots\})$ is called $T$-cyclic subspace generated by $v$. My question is: for a subspace $W$ on $V$,…
2
votes
0 answers

Kernels of pairwise relatively prime polynomials polynomials

I'm trying to find a reference for the following theorem in linear algebra. Theorem. Let $k$ be a field, let $\mathfrak{P} \subseteq k[x]$ be a set of representatives of the irreducible polynomials in $k[x]$ (for example, if $k$ is algebraically…
Zero
  • 3,643
  • 26
  • 52
2
votes
1 answer

On local rings $(R, \mathfrak m)$ such that $\text{Spec}(R)$ is disjoint union of $\text{Ass}(R)$ and $ \{\mathfrak m \}$

Let $(R, \mathfrak m)$ be a Noetherian local ring such that $\mathfrak m \notin \text{Ass}(R)$ and $\text{Spec}(R)=\text{Ass}(R)\cup \{\mathfrak m \}$. Then, must $R$ be Cohen-Macaulay? Of course the hypothesis implies $R$ has positive depth, but I…
2
votes
1 answer

If $x\in I$ is such that $\text{Supp}(0:_M x)\subseteq V(I)$ , then how to show that $x \notin \cup_{P\in \text{Ass}_R(M)\setminus V(I)} P $?

Let $M$ be a finitely generated module over a Noetherian ring $R$. Let $I$ be an ideal of $R$. Since Ass$_R (M)$ is finite, and $I\nsubseteq P$ for all $P\in$Ass$_R (M)\setminus V(I)$, so by prime avoidance $I\nsubseteq \cup_{P\in…
1
2 3
8 9