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1 vote

Kronecker product definition

I don't understand the definition you're using, but I'll tell you that the Wikipedia definition is correct. The point of the Kronecker product is that it is a basis-dependent form of the tensor produ …
Qiaochu Yuan's user avatar
15 votes
Accepted

Left-Module Structure on the Tensor Product ofTwo Left Modules

Let $R, S$ be two (unital and associative to be safe) algebras over a commutative ring $k$ and let $M, N$ be respectively a left $R$-module and a left $S$-module. Then we can define the tensor product …
Qiaochu Yuan's user avatar
11 votes

Can we test if an abelian group is finitely generated by taking tensor product?

First note that it's not necessary to consider the tensor products $A \otimes K$ for arbitrary fields $K$; $K$ has some prime subfield $k$, and $A \otimes K \cong (A \otimes k) \otimes_k K$, so all th …
Qiaochu Yuan's user avatar
8 votes
Accepted

Infinite dimensional irreducible representations of a tensor product

Nate's suggestion on math.SE works. We'll show that if $A = k[x, \partial_x]$ and $B = k[y, \partial_y]$ are both taken to be the Weyl algebra, then the module over $A_2 = A \otimes B \cong k[x, \part …
Qiaochu Yuan's user avatar
23 votes

Tensor product of fields over integers

Here is a self-contained argument. First, as Jeremy Rickard observes, $K \otimes K \cong K \otimes_k K$, where $k$ is the prime subfield of $K$ (so $\mathbb{Q}$ if $K$ has characteristic zero and $\ma …
Qiaochu Yuan's user avatar
5 votes

What are the basic possibilities for a tensor product of two fields?

For a), if $L$ is a finite Galois extension of $k$ with Galois group $G$, then $$L \otimes_k L \cong \prod_{g \in G} L$$ has $|G|$ prime ideals. For b), if $k = \mathbb{F}_p(a)$ and $L = k[x]/(x^p - …
Qiaochu Yuan's user avatar
8 votes
Accepted

A non-trivial probability measure on $2^{\mathbb R}$

$2^{\mathbb{R}}$, being a product of compact Hausdorff groups, is a compact Hausdorff group, so it has a normalized Haar measure ("flipping uncountably many coins").
Qiaochu Yuan's user avatar
7 votes
Accepted

Simple quotients of a triple tensor product

Both of these statements are true (at least if $H$ is semisimple). It suffices to prove the first one. By hypothesis there is a nonzero map $V_1 \otimes V_2 \otimes V_3 \to Q$. It dualizes to a nonzer …
Qiaochu Yuan's user avatar
10 votes

Why are tensors a generalization of scalars, vectors, and matrices?

I'd like to borrow a little from several of the answers given so far to give a "practical" perspective. Let $V$ be an $\mathbb{R}$-vector space. A tensor of type $(m, n)$ is an element of $V^{\otime …
4 votes

Tensor product of linear mappings versus chain complexes

It seems to me that your question is actually about something that is clearer in a more basic context than chain complexes. Fix a field $k$ and let's work instead in the category $C$ of pairs $(V, T)$ …
Qiaochu Yuan's user avatar