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Commutative rings, modules, ideals, homological algebra, computational aspects, invariant theory, connections to algebraic geometry and combinatorics.

38 votes
Accepted

Do there exist non-PIDs in which every countably generated ideal is principal?

No such ring exists. Suppose otherwise. Let $I$ be a non-principal ideal, generated by a collection of elements $f_\alpha$ indexed by the set of ordinals $\alpha<\gamma$ for some $\gamma$. Consid …
Hugh Thomas's user avatar
  • 6,327
1 vote
Accepted

Representation dimension of a special algebra

I don't think (*) is correctly copied from the paper. The corresponding claim in the paper is that every morphism from an indecomposable summand of $M$ except for the identity morphism from $T$ to $T …
Hugh Thomas's user avatar
  • 6,327
12 votes
2 answers
323 views

Easy way to understand theta basis for X-cluster algebras of finite type?

For $\mathcal A$-cluster algebras of finite type, it is very easy to describe the theta-basis: it consists of the cluster monomials. Is there any similarly easy way to describe the theta-basis for $\m …
Hugh Thomas's user avatar
  • 6,327
6 votes

Nonfree projective module over a regular UFD?

What about $R = \mathbb R[x,y,z]/\langle x^2+y^2+z^2-1\rangle$ and $M$ the projective module corresponding to the tangent bundle? This seems to satisfy your criteria except probably for factorialness …
Hugh Thomas's user avatar
  • 6,327
12 votes
1 answer
1k views

What is a good introduction to cluster algebras from surfaces?

What is a good reference for cluster algebras from surfaces, with a view to their connection to Teichmuller theory? In my view, that means it should start off with unpunctured surfaces (and in fact …
Hugh Thomas's user avatar
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