I was playing around with Toeplitz matrices, specifically skew-symmetric Toeplitz matrices. So the diagonal is a zero, every diagonal above (resp. below) the main diagonal is a negative of its counterpart below (resp. above). The image on the left below is an example. Then I additionally constrained such a matrix to have a descendingly sorted first row (so largest values are close to the diagonal) - this looks like the image on the right below.
Skewify[mat_] :=
Module[{n, m}, {n, m} = Dimensions@mat;
Table[Which[j == k, 0, j < k, 1, j > k, -1], {j, 1, m}, {k, 1, n}]*
mat]
GraphicsRow[
With[{mm = RandomReal[{-10, 10}, 20]}, {MatrixPlot[
Skewify[N@ToeplitzMatrix@mm]],
MatrixPlot[Skewify[N@ToeplitzMatrix@Reverse@Sort@mm]]}]]
Above is the Mathematica code for that. I am looking for some explanation of the following phenomenon for the eigenvectors of such matrices: They seem to sit on ellipses/circles/spirals around the origin.
{v1, v3, v5, v7} =
Eigenvectors[
Skewify[N@
ToeplitzMatrix@
Reverse@Sort@RandomReal[{-10, 10}, 100]]][[#]] & /@ {1, 3, 5,
7};
GraphicsGrid@
Partition[
ListPlot[(Tooltip[{Re[#1], Im[#1]}] &) /@ # ,
AspectRatio -> 1] & /@ {v1, v3, v5, v7}, 2]
Can someone point to me what could be going on here? I don't even have a clue where to start. If it is too big to answer here, any references/papers would be welcome too. (I am not a mathematician, just a classically trained engineer but I can take a stab at it).
Note: The above image is generated assuming the entries in the first row of the matrix are chosen uniformly at random from a symmetric interval (the RandomReal[{-20, 20}, 100] part); one can get other interesting plots by restricting these to be positive (e.g RandomReal[{0, 20}, 100]), negative and so on. Here is an example with RandomReal[{-20, 0}, 100]).
PROGRESS:
With an intention to do something like what is done for circulant matrices, for a $n\times n$ skew-symmetric Toeplitz matrix whose first row runs as $ \{0, a_2, a_3, \dots, a_{n}\}$ I have derived the eigenvector equation to be:
$$ \sum \limits_{k=m+1}^n a_{k-m+1} v_k - \sum \limits_{k=1}^{m-1} a_{m-k+1}v_k = \lambda v_m $$ for $m=1, 2, \dots, n$ assuming $v$ is an eigenvevtor and $v_m$ is its $m$-th component.
But now stuck at this point. How do I use the fact that $a_2 \geq a_3 \geq \dots \geq a_n$?


