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Algebraic varieties, stacks, sheaves, schemes, moduli spaces, complex geometry, quantum cohomology.
8
votes
Accepted
General conditions for normality of blow-up
Let $X=Spec(R)$. Blowing-up $Z=V(I)$ is the same as to look at $Proj$ of the graded ring $R[It]=\oplus_{j\geqslant 0} I^jt^j\subset R[t]$, the Rees ring associated to $I$.
Assume $R$ is a domain, inte …
7
votes
1
answer
1k
views
Automorphism groups of Hirzebruch surfaces
The Hirzebruch surfaces are the $\mathbb{P}^1$ bundles $\mathbb{F_n}$ ($n\geqslant 0$) which can be obtained projectivizing the rank $2$ vector bundles $\mathcal{O}_{\mathbb{P}^1}\oplus \mathcal{O}_{\ …
2
votes
1
answer
182
views
The target of a regular function in Non-archimedean analytic geometry
Let $(k,|\cdot|)$ be an algebraically closed field, complete wrt a (multiplicative) norm as in the framework of the Berkovich's analytic geometry. Given a commutative Banach $k$-algebra $\mathcal{A}\ …
1
vote
Accepted
The variety induced by an extension of a field
I decided to turn my comment into an answer not because it is complete but because I think it can be of use.
Let $z=(z_0:z_1:z_2)$ and $u=(u_1:\ldots:u_k)$ be homogeneous coordinates of $\mathbb{P}^2$ …
1
vote
Scheme-theoretic image and delta-invariants
Without any stronger hypothesis connecting $f$ and $g$ you should not expect that to happen.
The simplest instance is when $(X,o)$ is alrealdy non singular, say dimension 2: $(\mathbb{C}^2,o)$. In thi …
1
vote
2
answers
121
views
Rank of a linear combination of linear operators
I asked this question a few days ago in MathExchange and received no satisfatory answer. I hope it is well suited for MathOverflow.
Suppose I have two linear operators $X,\,Y$ on $\mathbb{C}^n$. Now l …