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Questions about the properties of vector spaces and linear transformations, including linear systems in general.

3 votes
Accepted

factorization of the product of a matrix element and its cofactor

For the main problem, we can use expansion by minors along the ith row to compute $\det(A_n) = (-1)^{i+1}(a(n)_{i1}\widetilde{a(n)_{i1}} - a(n)_{i2}\widetilde{a(n)_{i2}} + a(n)_{i3}\widetilde{a(n)_{i …
Steven Sivek's user avatar
  • 6,589
4 votes
Accepted

Conjugation in SU(2)

It's not hard to explicitly construct G using the quaternions, assuming P is not \pm Q, and I think this is worth working out in detail because I really like this picture of SU(2). Identify SU(2) wit …
Steven Sivek's user avatar
  • 6,589
4 votes
Accepted

Lifting bases for (Z/pZ)^n to Z^n

Here's a unified argument based on my comments to Scott's post that doesn't use quadratic reciprocity in any form. Suppose n=2 and p >= 5, and lift each line of slope i in Y(2,p) to a point (ai+pbi, …
Steven Sivek's user avatar
  • 6,589
15 votes

A random walk matrix has eigenvalue 1 with multiplicty 1 - why?

For large enough n, the matrix B = A + A2 + ... + An has positive entries since there's a path of length at most n connecting any two vertices. Thus by the Perron-Frobenius theorem B has a unique max …
Steven Sivek's user avatar
  • 6,589