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- \title{Analiticka geometrija \textbf{ispitni zadatak}}
- \author{Lazar Savic(dobio savete*pomoc oko uvoznih listi) }
- \begin{document}
- \pagestyle{empty}
- the coset space. For any measurable subset $E\subset G/H$ , we may easily choose
- a measurable function $\delta_E:G\to\mathbb{C}$ so that
- %prva formula/ koriscenje arraya{};
- \begin{equation}
- \nonumber
- \delta_E(g)=\delta_E^H(gH) = \left\{
- \begin{array}{l l}
- 1 & \quad \text{if $gH\in E$,}\\
- 0 & \quad \text{if $gH\notin E$.}
- \end{array} \right.
- \end{equation}
- %kraj prve formule
- We may then define an $H$–invariant quotient measure $\tilde{\mu}$ satisfying:
- %integrlana f 1
- \begin{equation}
- \nonumber
- \tilde{\mu}=\int_G \delta_E(g)d\mu(g) = \int_{G/H} \delta_E^H(gH)d\tilde{\mu}(gH),
- \end{equation}
- %kraj integralne f 1
- and
- %pocetak integralne f 2
- \begin{equation}
- \nonumber
- \int_Gf(g)d\mu(g)=\int_{G/H}f^H(gH)d\tilde{\mu}(gH),
- \end{equation}
- %kraj integralne f2
- for all integrable functions $f:G\to\mathbb{C}$. \hfill $\square$
- \textbf{Remarks} There is an analogous version of Theorem 1.5.1 for left coset spaces $H\backslash G$. Note that we are not assuming that $H$ is a normal subgroup of $G$. Thus $G/H$ (respectively $H\backslash G$) may not be a group.
- \textbf{Example 1.5.2} (\textbf{Left invariant measure on} $GL(n,\mathbb{R})/(O(n,\mathbb{R})\cdot \mathbb{R}^x)$)
- For $n\geq 2$, we now explicitly construct a left invariant measure on the generalized upper half-plane $\mathfrak{h}^n=GL(n,\mathbb{R})/(O(n,\mathbb{R})\cdot \mathbb{R}^x)$.Returning to the Iwasawa decomposition (Proposition 1.2.6), every $z\in\mathfrak{h}^n$ has a representation in the form $z = xy$ with
- %pocetak formule/matrica x{zavrseno};
- \begin{equation}
- \nonumber
- z = \begin{pmatrix}
- 1 & x_{1,2} & x_{1,3} & \cdots & & x_{1,n}\\
- & 1 & x_{2,3}& \cdots & & x_{2,n}\\
- & & & \ddots && \vdots\\
- &&&&1&x_{n-1,n}\\
- &&&&&1
- \end{pmatrix},
- y=\begin{pmatrix}
- y_1y_2\cdots y_{n-1}&&&&\\
- &y_2y_3\cdots y_{n-2}&&&\\
- &&\ddots&&\\
- &&& n &\\
- &&&&1
- \end{pmatrix},
- \end{equation}
- %kraj formule/matrica
- with $x_{i,j}\in\mathbb{R}$ for $1\leq i\leq j\leq n$ and $y_i>0$ $1\leq i\leq n$. Let $d^*z$ denote the left invariant measure on $\mathfrak{h}^n$. Then $d^*z$ has the property that
- %pocetak zvezdica formule
- \begin{equation}
- \nonumber
- d^*(gz)=d^*z
- \end{equation}
- %kraj zvezdica formule
- for all $g\in GL(n,\mathbb{R}).$
- \textbf{Proposition 1.5.3} \emph{The left invariant $GL(n,\mathbb{r})-$measure $d^*z$ on $\mathfrak{h}^n$ can be given explicitly by the formula \[d^z=d^*xd^*y\] where \[d^*x = \prod_{1\leq i\leq j\leq n}dx_{i,j}, \>\>\> d^*y = \prod_{k=1}^{n-1}y_k^{-k(n-k)-1}dy_k. \tag{1.5.4}\]}
- For example, for $n=2$, with $z = \begin{pmatrix}
- y & x\\
- 0 & 1
- \end{pmatrix}$,we have $d^*z = \frac{dxdy}{y^2}$ while for $n=3$ with
- %formula zagrada k_m
- \begin{equation}
- \nonumber
- z= \begin{pmatrix}
- y_1y_2 & x_{1,2} y_1 & x_{1,3}\\
- 0 & y_1 & x_{2,3}\\
- 0&0&1
- \end{pmatrix},
- \end{equation}
- %kraj formule zagrada k_m
- we have
- %pocetak formule laka
- \begin{equation}
- \nonumber
- d^*z = dx_{1,2}dx_{1,3}dx_{2,3}\frac{dy_1dy_2}{(y_1y_2)^3}.
- \end{equation}
- $kraj formule laka
- \emph{Proof} We sketch the proof. The group $GL(n,\mathbb{R})$ is generated by diagonal matrices, upper triangular matrices with 1s on the diagonal, and the Weyl group $W_n$ which consists of all $n\times n$ matrices with exactly one 1 in each row and column and zeros everywhere else. For example,
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