线性代数入门 Introductory Linear Algebra MATH106001

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这是一份leeds利兹大学MATH106001作业代写的成功案例

线性代数入门 Introductory Linear Algebra MATH106001
问题 1.

Let $F$ be the given hermitian matrix (3.4.14) and $w \in C$. Assume that
$d_{1}:=\operatorname{det} F(1, \ldots, n-1) \neq 0, \quad d_{2}:=F(2, \ldots, n) \neq 0, \quad d_{3}:=\operatorname{det} F(2, \ldots, n-1) \neq 0 .$
Then
$$
\operatorname{det} F(w)=\frac{d_{1} d_{2}}{d_{3}}\left(1-\frac{\left|w-w_{0}\right|^{2} d_{3}^{2}}{d_{1} d_{2}}\right)
$$

证明 .

where
$$
w_{0}=\frac{1}{w_{1 n}} \sum_{j=2}^{n-1} f_{n j} w_{j n}
$$
and
$$
[F(1, \ldots, n-1)]^{-1}=\left(w_{j k}\right)_{j, k=1}^{n-1} .
$$

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MATH106001 COURSE NOTES :

It follows from these equations that
$$
\rho_{n}=\frac{\operatorname{det} F(w)}{d_{2}} \text { and } \mu_{n}=\frac{\operatorname{det} F(w)}{d_{1}} .
$$
Hence $\rho_{n}=\rho_{n-1}\left(1-\varphi_{n} \psi_{n}\right)$ and $\mu_{n}=\mu_{n-1}\left(1-\varphi_{n} \psi_{n}\right)$.
If we define (this is the same $w_{0}$ as in formula (3.4.15))
$$
w_{0}=-\sum_{j=2}^{n-1} f_{n j} \nu_{j}=\overline{-\sum_{j=2}^{n-1} f_{1 j} \mu_{j}}
$$
then $\delta_{n}=w-w_{0}, \Delta_{n}=\overline{w-w_{0}}$ and
$$
\left|w-u_{0}\right|^{2}=\varphi_{n} \psi_{n} \rho_{n-1} \mu_{n-1} .
$$








线性代数入门 Introductory Linear Algebra MATH106001

0

这是一份leeds利兹大学MATH106001作业代写的成功案例

线性代数入门 Introductory Linear Algebra MATH106001
问题 1.


$$
T=\left(\begin{array}{ll}
3 & 2 \
0 & 1
\end{array}\right)
$$
we take it as the representation of a transformation with respect to the standard basis $T=\operatorname{Rep} \varepsilon_{2}, \mathcal{\varepsilon}{2}(t)$ and we look for a basis $B=\left\langle\vec{\beta}{1}, \vec{\beta}{2}\right\rangle$ such that $$ \operatorname{Rep}{B, B}(t)=\left(\begin{array}{cc}
\lambda_{1} & 0 \
0 & \lambda_{2}
\end{array}\right)
$$
that is, such that $t\left(\vec{\beta}{1}\right)=\lambda{1} \vec{\beta}{1}$ and $t\left(\vec{\beta}{2}\right)=\lambda_{2} \vec{\beta}{2}$. $$ \left(\begin{array}{ll} 3 & 2 \ 0 & 1 \end{array}\right) \vec{\beta}{1}=\lambda_{1} \cdot \vec{\beta}{1} \quad\left(\begin{array}{ll} 3 & 2 \ 0 & 1 \end{array}\right) \vec{\beta}{2}=\lambda_{2} \cdot \vec{\beta}_{2}
$$

证明 .

We are looking for scalars $x$ such that this equation
$$
\left(\begin{array}{ll}
3 & 2 \
0 & 1
\end{array}\right)\left(\begin{array}{l}
b_{1} \
b_{2}
\end{array}\right)=x \cdot\left(\begin{array}{l}
b_{1} \
b_{2}
\end{array}\right)
$$
has solutions $b_{1}$ and $b_{2}$, which are not both zero. Rewrite that as a linear system.
$$
(3-x) \cdot b_{1}+\begin{array}{r}
2 \cdot b_{2}=0 \
(1-x) \cdot b_{2}=0
\end{array}
$$

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MATH106001 COURSE NOTES :


$$
S=\left(\begin{array}{ll}
\pi & 1 \
0 & 3
\end{array}\right)
$$
(here $\pi$ is not a projection map, it is the number $3.14 \ldots$ ) then
$$
\left|\left(\begin{array}{cc}
\pi-x & 1 \
0 & 3-x
\end{array}\right)\right|=(x-\pi)(x-3)
$$
so $S$ has eigenvalues of $\lambda_{1}=\pi$ and $\lambda_{2}=3$. To find associated eigenvectors, first plug in $\lambda_{1}$ for $x$ :
$$
\left(\begin{array}{cc}
\pi-\pi & 1 \
0 & 3-\pi
\end{array}\right)\left(\begin{array}{l}
z_{1} \
z_{2}
\end{array}\right)=\left(\begin{array}{l}
0 \
0
\end{array}\right) \quad \Longrightarrow \quad\left(\begin{array}{l}
z_{1} \
z_{2}
\end{array}\right)=\left(\begin{array}{l}
a \
0
\end{array}\right)
$$
for a scalar $a \neq 0$, and then plug in $\lambda_{2}$ :
$$
\left(\begin{array}{cc}
\pi-3 & 1 \
0 & 3-3
\end{array}\right)\left(\begin{array}{l}
z_{1} \
z_{2}
\end{array}\right)=\left(\begin{array}{l}
0 \
0
\end{array}\right) \quad \Longrightarrow \quad\left(\begin{array}{l}
z_{1} \
z_{2}
\end{array}\right)=\left(\begin{array}{c}
-b /(\pi-3) \
b
\end{array}\right)
$$
where $b \neq 0$.