diff --git a/PMATH370/figures-cache/cobweb-26.dpth b/PMATH370/figures-cache/cobweb-26.dpth new file mode 100644 index 0000000..e69de29 diff --git a/PMATH370/figures-cache/cobweb-26.md5 b/PMATH370/figures-cache/cobweb-26.md5 new file mode 100644 index 0000000..d5bbc08 --- /dev/null +++ b/PMATH370/figures-cache/cobweb-26.md5 @@ -0,0 +1 @@ +\def \tikzexternallastkey {3D43B2100354074698CE67826ED7EC03}% diff --git a/PMATH370/figures-cache/cobweb-26.pdf b/PMATH370/figures-cache/cobweb-26.pdf new file mode 100644 index 0000000..7b97147 Binary files /dev/null and b/PMATH370/figures-cache/cobweb-26.pdf differ diff --git a/PMATH370/notes.pdf b/PMATH370/notes.pdf index d4836ce..2c81ea7 100644 Binary files a/PMATH370/notes.pdf and b/PMATH370/notes.pdf differ diff --git a/PMATH370/notes.tex b/PMATH370/notes.tex index acfc071..4372bb9 100644 --- a/PMATH370/notes.tex +++ b/PMATH370/notes.tex @@ -2439,8 +2439,8 @@ \section{Generated iterated function systems} \end{prf} \chapter{Complex Functions} +\refstepcounter{section} -\section{Foundations} \begin{defn*}[complex derivative] Let $f : \C \to \C$. Then, \begin{enumerate} @@ -2656,8 +2656,104 @@ \section{Construction} Then, $H(z) = H(e^{i\theta}) = e^{i\theta} + e^{-i\theta} = 2\cos\theta \in [-2,2]$. Therefore, $H$ is well-behaved (i.e., invertible) on $R \to \C \setminus [-2,2]$. + + \lecture{Mar 13} + Consider now $H(Q_0(z)) = H(z^2) = z^2 + \frac{1}{z^2}$. + Note that $Q_{-2}(H(z)) = (z+\frac{1}{z})^2 - 2 = z^2+\frac{1}{z^2}$. + Hence, $H(Q_0^n(z)) = Q_{-2}^n(H(z))$. + + This looks quite similar to $S(Q_c^n(x)) = \sigma^n(S(x))$ in $\R$. + We can say that $H$ plays a similar role as $S$. + In fact, (not course content), $Q_0$ and $Q_{-2}$ are \term*{conjugate} + because $H$ is a homeomorphism between them. + + Let $z_n$ be a diverging sequence $\abs{z_n} \to \infty$. + Note that $\abs{H(z_n)} = \abs{z_n + \frac{1}{z_n}} \geq \abs{z_n} - \frac{1}{\abs{z_n}} \to \infty$ + Therefore, the image of the sequence $|H(z_n)| \to \infty$ also diverges. + + Let $z \in \C \setminus [-2, 2]$. + Since $H$ is surjective, we know there exists a $w \in R$ such that $z=H(w)$, + and see that + \[ + \abs{Q_{-2}^n(z)} + = \abs{Q_{-2}^n(H(w))} + = \abs*{H\underbrace{(Q_0^n(w))}_{\to \infty}} \to \infty + \] + by the previous claim. + Hence, $z \not\in K_{-2}$ and we have that $K_{-2} \subseteq [-2,2]$. + + Finally, let $z \in [-2, 2]$. + By graphical analysis, + \begin{center} + \cobweb[1.7][domain=-2:2,ymin=-2,ymax=2]{(\x)^2 - 2}{25} + \end{center} + there is no way to escape the box. + That is, $z \in K_{-2}$, i.e., $[-2,2] \subseteq K_{-2}$. + + Therefore, $K_{-2} = [-2, 2]$, and we have that $J_{-2} =[-2,2]$. \end{sol} +\begin{prop}[Escape Criterion]\label{prop:esc} + If $\abs{z} \geq \abs{c} > 2$, then $\abs{Q_c^n(z)} \to \infty$. + In particular, $z \not\in K_c$. +\end{prop} +\begin{prf} + We can write + \[ \abs{Q_c(z)} = \abs{z^2+c} \geq \abs{z}^2 - \abs{c} \geq \abs{z}^2 - \abs{z} = \abs{z}(\abs{z}-1) \] + Suppose $\abs{z} > 2 + \lambda$ for some $\lambda > 0$. + Then, we have that $\abs{z} - 1 > 1+\lambda$. + Therefore, $\abs{Q_c(z)} \geq \abs{z}(1+\lambda)$. + + Iterating, we see that $\abs{Q_c^n(z)} \geq \abs{z}(1+\lambda)^n \to \infty$. +\end{prf} + +\begin{corollary} + Suppose $\abs{c} > 2$. Then, $\abs{Q_c^n(0)} \to \infty$ and $0 \not\in K_c$. +\end{corollary} +\begin{prf} + Let $z = Q_c(0) = c$ and $\abs{z} = \abs{c} > 2$. + By the \nameref{prop:esc}, $|Q_c^n(0)| \to \infty$. +\end{prf} + +\begin{corollary} + Let $M = \max\{\abs{c}, 2\}$. + If $\abs{z} > M$, then $\abs{Q_c^n(z)} \to \infty$. + That is, we have that $K_c \subseteq \{z : \abs{z} \leq M\}$. +\end{corollary} +\begin{prf} + We have $\abs{Q_c^n(z)} \geq (1+\lambda)^n\abs{z} \to \infty$ + by the proof of the Escape Criterion + (not the Escape Criterion itself because we don't know if $\abs{z} < 2$). +\end{prf} + +\begin{remark}[assignment hint!] + The fact that $K_c$ is inside this bounded disc will help with the proof of its closedness. +\end{remark} + +\begin{corollary} + If there exists a $k$ such that $\abs{Q_c^k(z)} > \max\{\abs{c}, 2\}$, + then $\abs{Q_c^n(z)} \to \infty$. + That is, $z \not\in K_c$. +\end{corollary} + +Based on these results, we can develop the + +\begin{algorithm}[H] + \caption{Filled Julia set algorithm} + \begin{algorithmic}[1] + \State Choose a large $N \in \N$. + \For{points $z$} + \If{$\abs{Q_c^i(z)} > \max\{\abs{c},2\}$ for any $i \leq N$} + \State Colour $z$ white + \ElsIf{$\abs{Q_c^i(z)} \leq \max\{\abs{c},2\}$ for all $i \leq N$} + \State Colour $z$ black + \EndIf + \EndFor + \end{algorithmic} +\end{algorithm} + +whose black-shaded region approximates $K_c$. + \pagebreak \phantomsection\addcontentsline{toc}{chapter}{Back Matter} \renewcommand{\listtheoremname}{List of Named Results} diff --git a/latex/agony-pmath370.tex b/latex/agony-pmath370.tex index 55d54f5..928dd84 100644 --- a/latex/agony-pmath370.tex +++ b/latex/agony-pmath370.tex @@ -27,6 +27,8 @@ \usetikzlibrary{hobby,arrows.meta,decorations.fractals,lindenmayersystems} \RequirePackage{pstricks,pst-fractal} % for Sierpinski +\RequirePackage{algorithm,float} +\RequirePackage[noEnd]{algpseudocodex} \pgfdeclarelindenmayersystem{box fractal}{ \rule{F -> F+F-F-F+F}