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Aug 2, 2010 at 13:09 history edited Ryan Reich CC BY-SA 2.5
specify different eigenvalue
Aug 2, 2010 at 6:19 history edited Ryan Reich CC BY-SA 2.5
Fix fix.
Aug 2, 2010 at 5:37 comment added Ryan Reich Fixed!$ $
Aug 2, 2010 at 5:37 history edited Ryan Reich CC BY-SA 2.5
Fix construction
Aug 2, 2010 at 4:35 comment added Joel David Hamkins But what I don't see is that your basis statement is expressible in the language of matrix algebra independently of the dimension. For any fixed n it seems fine, but what we need is one statement in that language, whose truth varies as n increases.
Aug 2, 2010 at 4:23 comment added Ryan Reich I only need one basis, so I don't have to quantify over sets of vectors. That is, $e_1, \dots, e_n$ is a real basis if for all real scalars $a_1, \dots, a_n$ we don't have $\sum a_j e_j = 0$, and if for all vectors $v$ we have real scalars $a_j, b_j$ such that $\sum a_j e_j + \sum i b_j e_j = v$. Then a matrix $A$ is "real" if each $A e_j$ is in the real span of the $e_j$ and $n$ is even iff there exists a real $A$ with $A^2 e_j = -e_j$ for each vector in the real basis.
Aug 2, 2010 at 3:59 comment added Joel David Hamkins I don't follow your remarks about the basis. You can't quantify over sets of vectors, but just over vectors (and matrices and scalars).
Aug 2, 2010 at 3:03 history edited Ryan Reich CC BY-SA 2.5
Cover complex case.
Aug 2, 2010 at 1:29 history answered Ryan Reich CC BY-SA 2.5