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2 changes: 1 addition & 1 deletion wiki/acknowledgements.md
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Expand Up @@ -19,7 +19,7 @@ permalink: /acknowledgements/
## Support

- Supported by [Centre for Theoretical Physics, Polish Academy of
Sciences](http://www.cft.edu.pl/en/).
Sciences](http://www.cft.edu.pl).

- Hosted and maitained by [Institute of Theoretical and Applied
Informatics, Polish Academy of Sciences](http://www.iitis.pl/en/).
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4 changes: 2 additions & 2 deletions wiki/index.md
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Expand Up @@ -39,12 +39,12 @@ is forming an image of $\mathbb{R}P^1 \times \mathbb{R}P^1$.

## Page created by
* [Łukasz Pawela](https://www.iitis.pl/en/person/lpawela)
* [Piotr Gawron](https://pgawron.github.io)
* [Piotr Gawron](https://piotrgawron.eu/)
* [Jarosław Adam Miszczak](https://www.iitis.pl/en/person/jmiszczak)
* [Zbigniew Puchała](https://www.iitis.pl/en/person/zpuchala)
* [Karol Życzkowski](http://chaos.if.uj.edu.pl/~karol/)
* [Paulina Lewandowska](https://www.iitis.pl/en/node/2654)
* [Ryszard Kukulski](https://iitis.pl/en/node/2619)
* [Ryszard Kukulski](https://scholar.google.pl/citations?user=Lict0ugAAAAJ&hl=en)


## Support
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4 changes: 2 additions & 2 deletions wiki/numerical-range.md
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Expand Up @@ -14,9 +14,9 @@ range* (also called *field of values* {% cite murnaghan1932field %}) as a
subset of the complex plane:

$$
W(A)=\\{ z \in \mathbb{C}: z=\bra{\psi}
W(A)=\{ z \in \mathbb{C}: z=\bra{\psi}
A\ket{\psi}, \\ \ket{\psi} \in {\mathbb{C}}^d, \\
\braket{\psi}{\psi}=1\\}.
\braket{\psi}{\psi}=1 \}.
$$

Following a common convention we denote here
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2 changes: 1 addition & 1 deletion wiki/numerical-range/examples/2x2.md
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Expand Up @@ -9,7 +9,7 @@ permalink: /numerical-range/examples/2x2/

- For a Jordan matrix $J=\begin{pmatrix}0&1\\\0&0\end{pmatrix}$ the
numerical range forms a circular disk of radius one half, $W(J) =
D(0,)$.
D(0, 0.5)$.

| Example of a circular numerical range. |
| --- |
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35 changes: 17 additions & 18 deletions wiki/numerical-range/examples/4x4.md
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Expand Up @@ -7,8 +7,7 @@ permalink: /numerical-range/examples/4x4/
---
### Example 1

A generic matrix $M=\begin{pmatrix} 1 & 1 & 1 & 1\ 0 & \ii & 1 & 1\ 0
& 0 & -1 & 1\ 0 & 0 & 0 & \ii \end{pmatrix}$ has an oval–like numerical
A generic matrix $M=\begin{pmatrix}1&1&1&1\\\0&\ii&1&1\\\0& 0 & -1 & 1 \\\ 0 & 0 & 0 & \ii \end{pmatrix}$ has an oval–like numerical
range $W (M)$.

| |
Expand All @@ -17,8 +16,8 @@ range $W (M)$.

### Example 2

The matrix $M=\begin{pmatrix} 1 & 1 & 1 & 1\ 0 & \ii & 1 & 1\ 0 & 0 & -1
& 1\ 0 & 0 & 0 & \ii \end{pmatrix}$ has a numerical range $W (M)$ with
The matrix $M=\begin{pmatrix} 1 & 1 & 1 & 1 \\\ 0 & \ii & 1 & 1 \\\ 0 & 0 & -1
& 1 \\\ 0 & 0 & 0 & \ii \end{pmatrix}$ has a numerical range $W (M)$ with
one flat part of the boundary $\partial W$.

| |
Expand All @@ -27,8 +26,8 @@ one flat part of the boundary $\partial W$.

### Example 3

The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 1\ 0 & \ii & 0 & 1\ 0 & 0 & -1
& 0\ 0 & 0 & 0 & 1 \end{pmatrix}$ has a numerical range $W (M)$ with two
The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 1 \\\ 0 & \ii & 0 & 1 \\\ 0 & 0 & -1
& 0 \\\ 0 & 0 & 0 & 1 \end{pmatrix}$ has a numerical range $W (M)$ with two
flat parts of of the boundary $\partial W$.

| |
Expand All @@ -37,8 +36,8 @@ flat parts of of the boundary $\partial W$.

### Example 4

The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 1\ 0 & \ii & 1 & 0\ 0 & 0 & -1
& 0\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ with
The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 1 \\\ 0 & \ii & 1 & 0 \\\ 0 & 0 & -1
& 0 \\\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ with
two parallel flat parts of of the boundary $\partial W$.

| |
Expand All @@ -47,8 +46,8 @@ two parallel flat parts of of the boundary $\partial W$.

### Example 5

The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 1\ 0 & \ii & 0 & 0\ 0 & 0 & -1
& 0\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ with
The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 1 \\\ 0 & \ii & 0 & 0 \\\ 0 & 0 & -1
& 0 \\\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ with
three flat parts of $\partial W$ connected with corners and one
oval–like part.

Expand All @@ -58,8 +57,8 @@ oval–like part.

### Example 6

The matrix $M=\begin{pmatrix} \ii & 0 & -1 & 0\ 0 & 0 & -1 & 0\ 1 & 1
& 1-\ii & 0\ 0 & 0 & 0 & 1 \end{pmatrix}$ has a numerical range $W (M)$
The matrix $M=\begin{pmatrix} \ii & 0 & -1 & 0 \\\ 0 & 0 & -1 & 0 \\\ 1 & 1
& 1-\ii & 0 \\\ 0 & 0 & 0 & 1 \end{pmatrix}$ has a numerical range $W (M)$
with three flat parts of $\partial W$ with only one corner and two
oval–like parts.

Expand All @@ -69,8 +68,8 @@ oval–like parts.

### Example 7

The matrix $M=\begin{pmatrix} 1 & 0 & 1 & 0\ 0 & \ii & 0 & 1\ 0 & 0 & -1
& 0\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ with
The matrix $M=\begin{pmatrix} 1 & 0 & 1 & 0 \\\ 0 & \ii & 0 & 1 \\\ 0 & 0 & -1
& 0 \\\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ with
four flat parts of $\partial W$.

| |
Expand All @@ -79,8 +78,8 @@ four flat parts of $\partial W$.

### Example 8

The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 0\ 0 & \ii & 0 & 1\ 0 & 0 & -1
& 0\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ pair
The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 0 \\\ 0 & \ii & 0 & 1 \\\ 0 & 0 & -1
& 0 \\\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ pair
of flat parts of $\partial W$ connected with a corner connected with two
oval–like parts.

Expand All @@ -90,8 +89,8 @@ oval–like parts.

### Example 9

The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 0\ 0 & \ii & 0 & 0\ 0 & 0 & -1
& 0\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ equal
The matrix $M=\begin{pmatrix} 1 & 0 & 0 & 0 \\\ 0 & \ii & 0 & 0 \\\ 0 & 0 & -1
& 0 \\\ 0 & 0 & 0 & -\ii \end{pmatrix}$ has a numerical range $W (M)$ equal
to the convex hull of eigenvalues.

| |
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26 changes: 17 additions & 9 deletions wiki/numerical-range/examples/doubly-stochastic.md
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Expand Up @@ -12,14 +12,22 @@ permalink: /numerical-range/examples/numerical-range-of-doubly-stochastic-matric
A doubly stochastic matrix $A \in \mathbb{R}^{n \times n }$ is a matrix
for which the entries are non-negative while the row and column sums are
all equal to one $\sum_{j=1}^{n} a_{ij} = 1 \text{ for } i=1,\ldots,n$
and $\sum_{i=1}^{n} a_{ij} = 1 \text{ for } j=1,\ldots,n$
and $\sum_{i=1}^{n} a_{ij} = 1 \text{ for } j=1,\ldots,n$.

### Theorem

Let A be $4\times 4$ doubly stochastic matrix. Then, $ W(A)$consists of
elliptical arcs and line segments if and only if$$ := (A) - 1 + $is an
eigenvalue of A (multiple, if $$\mu =1$$). If, in addition$ A - 1 - 3\>0
, (A -1 - 3)^2 - (A^A) + 1 +2 + ^2 \> 0 \$\$\$\$
Let A be $4\times 4$ doubly stochastic matrix. Then, $ W(A)$ consists of
elliptical arcs and line segments if and only if

$$
\mu := \tr(A) - 1 + \frac{\tr(A^3) - \tr(A^\top A^2)}{\tr(A^\top A) - \tr(A^2)}
$$

is an eigenvalue of $A$ (multiple, if $\mu =1$). If, in addition

$$
\tr(A) - 1 - 3 \mu >0, (\tr(A) -1 - 3 \mu)^2 - \tr(A^\top A) + 1 +2 \det(A) / \mu + \mu^2 > 0,
$$

then $W(A)$ also has corner points at $\mu$ and 1, and thus four flat
portions on the boundary. Otherwise, 1 is the only corner point of
Expand All @@ -29,8 +37,8 @@ elliptical arc.
### Example 1

Consider the doubly stochastic matrix : $A =
\begin{pmatrix} 0&1/3&1/4&5/12\ 1/3&0&1/2&1/6\ 1/4&9/32&1/4&1/6\ 5/12&37/96&0&19/96
\end{pmatrix}$
\begin{pmatrix} 0&1/3&1/4&5/12\\\ 1/3&0&1/2&1/6\\\ 1/4&9/32&1/4&1/6\\\ 5/12&37/96&0&19/96
\end{pmatrix}$.

Using above theorem, we compute $\mu = -1/3.$ By calculating the
characteristic polynomial and computin the conditions from Theorem we
Expand All @@ -47,8 +55,8 @@ Fig. 1 we give $W(A)$, and the horizontal ellipse it contains, $W(A_1)$.
### Example 2

Consider the doubly stochastic matrix : $A =
\begin{pmatrix} 0&1/3&1/4&5/12\ 1/3&0&1/2&1/6\ 1/4&1/8&1/4&3/8\ 5/12&13/24&0&1/24
\end{pmatrix}$ By coincidence, we again compute $\mu = -1/3$, and though
\begin{pmatrix} 0&1/3&1/4&5/12\\\ 1/3&0&1/2&1/6\\\ 1/4&1/8&1/4&3/8\\\ 5/12&13/24&0&1/24
\end{pmatrix}$. By coincidence, we again compute $\mu = -1/3$, and though
the characteristic polynomial again has $\mu$ as a root. The formulas in
inequalities on Theorem evaluate to $7/24$ and $59/576$ respectively, so
the number of flat portions is still the same. However, Fig. 2 shows
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9 changes: 4 additions & 5 deletions wiki/numerical-range/examples/ginibre.md
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Expand Up @@ -11,8 +11,7 @@ The figures below depict numerical range for large random matrices drawn
from different ensembles. Gray areas denote numerical ranges and red
dots denote spectra of matrices.

Matrices are normalized so that for every matrix $A$
$\Tr(AA^\dagger)=\dim(A)$.
Matrices are normalized so that for every matrix $A$, $\Tr(AA^\dagger)=\dim(A)$.

In the figures below

Expand All @@ -29,7 +28,7 @@ largest modulus.
Complex Ginibre matrices $G_d$ of dimention $d$ with entries $\xi_{ij}$,
where $\mathbb{E} \|\xi _{ij}\|^2 =1/d$. As we mention in the
introduction, by the circular law, the spectrum of $G_N$ is
asymptotically contained in the unit disk. Note $ \\|G\_d\\| \_{}^2=d$.
asymptotically contained in the unit disk. Note $\mathbb{E} \\|G\_d\\| \_{}^2=d$.

Upper triangular random matrices $T_d$ of dimension $d$ with entries
$T_{ij}=\xi_{ij}$ for $i \<j$ and $T_{ij}=0$ elsewhere, where
Expand All @@ -42,8 +41,8 @@ denote complex eigenvalues of $G_d$. In order to ensure the uniqueness
of the probability distribution on diagonal matrices, we assume that it
is invariant under conjugation by permutations. Note that integrating
over the Girko circular law one gets the average squared eigenvalue of
the complex Ginibre matrix, $||<sup>2=*{0}^1 2x^3 dx=1/2$. Thus,$
\\|D\_d\\| *{}</sup>2=d/2$.
the complex Ginibre matrix, $ \int \_{0}^{1} 2x^3 dx=1/2$. Thus, $
\mathbb{E} \\|D\_d\\|^2=d/2$.

Diagonal unitary matrices $U_d$ of order $d$ with entries $U_{kl}=\exp(i
\phi_k) \delta_{kl}$, where $\phi_k$ are independent uniformly
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2 changes: 2 additions & 0 deletions wiki/numerical-range/generalizations.md
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Expand Up @@ -42,5 +42,7 @@ permalink: /numerical-range/generalizations/
`B`](/numerical-range/generalizations/numerical-range-of-a-with-respect-to-b)
- [Maximal numerical
range](/numerical-range/generalizations/maximal-numerical-range)
- [Joint numerical
range](/numerical-range/generalizations/joint-numerical-range)
- [Essential numerical
range](/numerical-range/generalizations/essential-numerical-range)
2 changes: 1 addition & 1 deletion wiki/numerical-range/generalizations/c-numerical-range.md
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Expand Up @@ -83,7 +83,7 @@ we denote all $p$-Schatten-class operators defined by
\mathcal{B}^p(\mathcal{X}, \mathcal{Y}) \coloneqq \\{ C \in \mathcal{K}(\mathcal{X}, \mathcal{Y}) | \sum_{n=1}^\infty s_n(C) ^p < \infty \\}
\end{equation}

for $p \[1,\infty )$ whereas the Schatten-$p$-norm of matrix $A$
for $p \in \[1,\infty )$ whereas the Schatten-$p$-norm of matrix $A$
$$
\| A \|_p \coloneqq \left( \sum_{n=1}^\infty s_n(A)^p \right)^{1/p},
$$
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Expand Up @@ -24,9 +24,9 @@ the essential numerical range of $T$ by $W_e(T ) = \\{\lambda \in

### Properties

For any $z \in \mathbb{C}$ and let $\sigma_e(T) = \\{ \lambda \in
For any $z \in \mathbb{C}$ and $\sigma_e(T) = \\{ \lambda \in
\mathrm{C} : \exists (x_n)_{n \in \mathbb{N}} \subset \mathcal{D}(T )
\\,\\,\\, \text{with} \\,\\,\\, \|\|xn\|\| = 1, (x_n) \rightarrow 0,
\\,\\,\\, \text{with} \\,\\,\\, \|\|x\_n\|\| = 1, (x_n) \rightarrow 0,
\|\|(T- \lambda)x_n \|\| \rightarrow 0 \\}$ then we have
{% cite bogli2020essential %}

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Expand Up @@ -9,8 +9,8 @@ permalink: /numerical-range/generalizations/numerical-range-of-a-with-respect-to

### Example 1

Diagonal matrix $A=\begin{pmatrix} 1 & 0 & 0 & 0\ 0 & 1+2\ii & 0 & 0\ 0
& 0 & 3\ii & 0\ 0 & 0 & 0 & 0 \end{pmatrix}$ with respect to matrix $B
Diagonal matrix $A=\begin{pmatrix} 1 & 0 & 0 & 0\\\ 0 & 1+2\ii & 0 & 0\\\ 0
& 0 & 3\ii & 0\\\ 0 & 0 & 0 & 0 \end{pmatrix}$ with respect to matrix $B
=\1_4$.

#### Trace norm
Expand All @@ -23,15 +23,17 @@ Diagonal matrix $A=\begin{pmatrix} 1 & 0 & 0 & 0\ 0 & 1+2\ii & 0 & 0\ 0

#### Infinity norm

![]({{ "/assets/numerical-range/generalizations/nr_diagonal_id_inf.gif" | relative_url }}) Under this
![]({{ "/assets/numerical-range/generalizations/nr_diagonal_id_inf.gif" | relative_url }})

Under this
assumption, the numerical range $w_{\|\|\cdot\|\|_\infty}(A;\1_4)=
W(A)$.

### Example 2

Matrix $A=\begin{pmatrix} 6+\ii & 0.4 & 0 & -0.1\ 0.1 & 1-3\ii & -0.3\ii
& 0\ 0 & 0 & 0.5 & 0 \end{pmatrix}$ with respect to matrix
$B=\begin{pmatrix} 1.2 & 0 & 0 & 0\ 0 & \ii & 0 & 0\ 0 & 0 & -1 & 0
Matrix $A=\begin{pmatrix} 6+\ii & 0.4 & 0 & -0.1\\\ 0.1 & 1-3\ii & -0.3\ii
& 0\\\ 0 & 0 & 0.5 & 0 \end{pmatrix}$ with respect to matrix
$B=\begin{pmatrix} 1.2 & 0 & 0 & 0\\\ 0 & \ii & 0 & 0\\\ 0 & 0 & -1 & 0
\end{pmatrix}$

#### Trace norm
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Expand Up @@ -17,10 +17,14 @@ and [numerical range of rectangular
matrices]({{ "/numerical-range/generalizations/numerical-range-of-a-with-respect-to-b" | relative_url }}).

Let $M,N$ be positive integers, that satisfy $M \geq N$. For every $k
\in \\{1,\ldots,N\\}$ define the following set: $\mathcal{X}= \left\\{
\in \\{1,\ldots,N\\}$ define the following set:

$$
\mathcal{X} = \left\\{
(X,Y): X \mbox{ is } N \times (N-k+1) \mbox{ isometry matrix },
Y=\left\[ \begin{array}{c\|c} X & 0\ \hline 0 & U \end{array} \right\],U
\in \mathcal{U}_{M-N} \right\\}.$
\in \mathcal{U}_{M-N} \right\\}.
$$

## Definition

Expand Down Expand Up @@ -60,20 +64,20 @@ induced matrix norm and for every unit vector $z$ and for all $(X,Y) \in

## Example 1

Diagonal matrix $A=\begin{pmatrix} 1 & 0 & 0 & 0\ 0 & 1+2\ii & 0 & 0\ 0
& 0 & 3\ii & 0\ 0 & 0 & 0 & 0 \end{pmatrix}$ with respect to matrix $B
=\1_4$ with $\|\|\cdot\|\| = \|\|\cdot\|\|_\infty$. Then,
$\Lambda_{k,\|\|\cdot\|\|}(A;B) = \Lambda_k(A)$ is $k$--numerical range
Diagonal matrix $A=\begin{pmatrix} 1 & 0 & 0 & 0\\\ 0 & 1+2\ii & 0 & 0\\\ 0
& 0 & 3\ii & 0\\\ 0 & 0 & 0 & 0 \end{pmatrix}$ with respect to matrix $B
=\1\_{4}$ with $\|\| \\cdot \|\| = \|\| \cdot \|\|_\infty$. Then,
$ \Lambda\_{k,\|\|\cdot\|\|}(A;B) = \Lambda\_k(A)$ is $k$--numerical range
of $A$. In this case, $k=2$.

![]({{ "/assets/numerical-range/generalizations/2k_nr_diagonal.png" | relative_url }})

## Example 2

Matrix $A=\begin{pmatrix} 6+\ii & 0.4 & 0 & -0.1\ 0.1 & 1-3\ii & -0.3\ii
& 0\ 0 & 0 & 0.5 & 0 \end{pmatrix}$ with respect to matrix
$B=\begin{pmatrix} 1.2 & 0 & 0 & 0\ 0 & \ii & 0 & 0\ 0 & 0 & -1 & 0
\end{pmatrix}$ with $|||| = ||||\_$and$k=1$. Then,
Matrix $A=\begin{pmatrix} 6+\ii & 0.4 & 0 & -0.1\\\ 0.1 & 1-3\ii & -0.3\ii
& 0\\\ 0 & 0 & 0.5 & 0 \end{pmatrix}$ with respect to matrix
$B=\begin{pmatrix} 1.2 & 0 & 0 & 0\\\ 0 & \ii & 0 & 0\\\ 0 & 0 & -1 & 0
\end{pmatrix}$ with $\|\| \cdot \|\| = \|\| \cdot \|\|\_2$ and $k=1$. Then,
$\Lambda_{1,\|\|\cdot\|\|}(A;B) = w_{\\\| \cdot \\\|}(A; B)$.
![]({{ "/assets/numerical-range/generalizations/1k_nr_rectangular.png" | relative_url }})

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Expand Up @@ -78,7 +78,7 @@ when:
## Theorem for Hermitian matrices

Let $A$ will be Hermitian matrix of dimenasion $n$ and let $pk \le n$. The
set $\Lambda_{p,k}(A) \emptyset $ if and only if $\lambda_{jk}(A) \geq
set $\Lambda_{p,k}(A) \neq \emptyset $ if and only if $\lambda_{jk}(A) \geq
\lambda_{n-(p-j+1)k+1}(A) \quad \text{for } j=1,\ldots,p.$

Furthermore, for a given matrix $B \in M_n$ we can obtain
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Expand Up @@ -35,7 +35,7 @@ properties of $W(p:A)$.
Let $A \in M_n$ will be any matrix of dimension $n$, then in general
case the set $W(p:A)$ is non-convex {% cite thompson1987research %}. The
following theorems (see {% cite li1991k %}) give us the conditions to
matrix $A$ and its eigenvalues so as to the set $W(p:A) will be convex.
matrix $A$ and its eigenvalues so as to the set $W(p:A)$ will be convex.

### Theorem

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2 changes: 1 addition & 1 deletion wiki/numerical-range/generalizations/q-numerical-range.md
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Expand Up @@ -28,7 +28,7 @@ Properties of $W_q(A)$ of a matrix $A$ of dimension $d \times d$
## Example

The numerical aproximation of $W_{13/14}(A)$, where $A =
\begin{pmatrix} 0&1&1/2\ 0&0&1\ 0&0&0 \end{pmatrix}.$
\begin{pmatrix} 0&1&1/2\\\ 0&0&1\\\ 0&0&0 \end{pmatrix}.$

![]({{ "/assets/numerical-range/qnr1.png" | relative_url }})

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Expand Up @@ -9,7 +9,7 @@ permalink: /numerical-range/generalizations/restricted-numerical-range/

## Definition

Restricted numerical range of an $d \times d$ matrix $A$ is defined as:
Restricted numerical range of an $d \times d$ matrix $A$ is defined as
$W_\mathrm{R}(A) = \left\\{ \mathrm{Tr}A\rho, \\; \rho \in
\Omega_\mathrm{R} \subset \Omega \right\\}$. The symbol
$\Omega_\mathrm{R}$ denotes any arbitrary subset of set $\Omega$ of all
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