Let $A$ be an $n\times n$ real matrix with entries in a fixed interval $[a\_\min,a\_\max]$, with $a\_\min$, $a\_\max>0$.



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> **Question:** Are there any upper bounds on the condition number of the eigenvector matrix associated to $A$ as $n$ increases?
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The motivation of this question comes from the $n\times n$ random dense case. Indeed, with reference to this case, in [1, Page 338] it is stated that: *"[...] experiments indicate that the condition number of the associated eigenvector matrix also grows **linearly** [as $n$ increases]"*.


Hence, I wonder whether any similar result can be/has been proved for the deterministic (positive) dense case.


**[1]** L. N. Trefethen and M. Embree. *Spectra and pseudospectra: the behavior of nonnormal matrices and operators*. Princeton University Press, 2005.



Upper bounds on the condition number of the eigenvector matrix
**No, there are no such bounds.**


Let $a>0$ be a fixed real and $\varepsilon\ll a$. Take the non-diagonalizable matrix $A=\begin{bmatrix}3a & 0 & 0\\ 0 & 0 & \varepsilon \\ 0 & 0 & 0 \end{bmatrix}$. Let $V$ be a symmetric, orthogonal matrix that maps $\begin{bmatrix}\sqrt {3}\\0\\0\end{bmatrix}$ to $\begin{bmatrix}1\\1\\1\end{bmatrix}$ (for instance, a [Householder reflector](https://en.wikipedia.org/wiki/Householder_transformation)).


Now $M=VAV^{-1}$ has entries in $[a-O(\varepsilon),a+O(\varepsilon)]$ and is not diagonalizable. So the eigenvector condition number of any sequence of matrices $M\_k$ that converges to $M$ blows up.


