From 84594916dd6f7d67b54a8ff078b5e1afffe56682 Mon Sep 17 00:00:00 2001
From: Zheyuan Wu <60459821+Trance-0@users.noreply.github.com>
Date: Fri, 24 Jan 2025 11:48:20 -0600
Subject: [PATCH] update

---
 pages/CSE559A/CSE559A_L3.md   |   0
 pages/CSE559A/CSE559A_L4.md   |   0
 pages/CSE559A/_meta.js        |   6 +-
 pages/Math4121/Math4121_L5.md | 120 +++++++++++++++++++++++++++++++++-
 4 files changed, 123 insertions(+), 3 deletions(-)
 create mode 100644 pages/CSE559A/CSE559A_L3.md
 create mode 100644 pages/CSE559A/CSE559A_L4.md

diff --git a/pages/CSE559A/CSE559A_L3.md b/pages/CSE559A/CSE559A_L3.md
new file mode 100644
index 0000000..e69de29
diff --git a/pages/CSE559A/CSE559A_L4.md b/pages/CSE559A/CSE559A_L4.md
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diff --git a/pages/CSE559A/_meta.js b/pages/CSE559A/_meta.js
index 2d3ca47..e6563d1 100644
--- a/pages/CSE559A/_meta.js
+++ b/pages/CSE559A/_meta.js
@@ -3,6 +3,8 @@ export default {
     "---":{
         type: 'separator'
     },
-    CSE559A_L1: "Cmputer Vision (Lecture 1)",
-    CSE559A_L2: "Cmputer Vision (Lecture 2)",
+    CSE559A_L1: "Computer Vision (Lecture 1)",
+    CSE559A_L2: "Computer Vision (Lecture 2)",
+    CSE559A_L3: "Computer Vision (Lecture 3)",
+    CSE559A_L4: "Computer Vision (Lecture 4)",
 }
diff --git a/pages/Math4121/Math4121_L5.md b/pages/Math4121/Math4121_L5.md
index 23c2f01..1a399f5 100644
--- a/pages/Math4121/Math4121_L5.md
+++ b/pages/Math4121/Math4121_L5.md
@@ -1 +1,119 @@
-# Lecture 5
\ No newline at end of file
+# Lecture 5
+
+## Continue on differentiation
+
+### L'Hôpital's Rule
+
+Suppose $f$ and $g$ are real differentiable on $(a,b)$ and $g'(x)\neq 0$ for all $x\in (a,b)$.
+
+Suppose $\frac{f'(x)}{g'(x)}\to A$ as $x\to a$,
+
+If $f(x)\to 0$ and $g(x)\to 0$ as $x\to a$,
+
+or $g(x)\to \infty$ as $x\to a$,
+
+then $\frac{f(x)}{g(x)}\to A$ as $x\to a$.
+
+Proof:
+
+**Main step: Let $-\infty<a<b<\infty$.for any $q>A$, there exists $c\in (a,b)$ such that $\frac{f(x)}{g(x)}<q$ for all $x\in (a,c)$.**
+
+> Topological definition of limit:
+>
+> $h(x)\to A$ as $x\to a$ if $\forall \epsilon>0$, $\exists \delta>0$ such that $|x-a|<\delta$ implies $|h(x)-A|<\epsilon$.
+>
+> In other words, if for any open neighborhood $V$ of $A$, there exists an open neighborhood $U$ of $a$ such that $h(U)\subseteq V$.
+
+Case 1: $A=-\infty$, for any $q>A$, there exists $\delta>0$ such that $x\in (a,a+\delta)$ implies $\frac{f(x)}{g(x)}<q$.
+
+Case 2: $A=\infty$, we change the function $F(x)=-f(x)$ and apply the case 1.
+
+Case 3: $A\in \mathbb{R}$, Let $\epsilon>0$ and take $q=A+\epsilon$. $\exists c_1\in (a,b)$ such that $\forall x\in (a,c_1)$, $\frac{f(x)}{g(x)}<q$.
+
+Set $F(x)=-f(x)$. and $q=-A+\epsilon>-A$. Apply main step, $\exists c_2\in (a,b)$ such that $\forall x\in (a,c_2)$, $\frac{F(x)}{g(x)}<-A+\epsilon$. so $\forall x\in (a,c_2)$, $\frac{f(x)}{g(x)}>A-\epsilon$.
+
+We take $c=\min(c_1,c_2)$. Then $\forall x\in (a,c)$, $\frac{f(x)}{g(x)}<q$.
+
+EOP
+
+### Higher Order Derivatives
+
+#### Definition 5.14
+
+If $f$ is differentiable on $(a,b)$, then we define $f'(x)=\lim_{t\to x}\frac{f(t)-f(x)}{t-x}$.
+
+If $f'$ is differentiable on $(a,b)$, then we define $f''(x)=(f')'(x)$.
+
+If $f^{(k)}$ is differentiable on $(a,b)$, then we define $f^{(k+1)}(x)=(f^{(k)})'(x)$.
+
+#### Theorem 5.15 Taylor's Theorem
+
+Let $f:[a,b]\to \mathbb{R}$, and $n$ be a positive integer.
+
+Let $f^{(n-1)}$ be continuous on $[a,b]$, and differentiable on $(a,b)$.
+
+For $\alpha\in [a,b]$, define the Taylor polynomial of order $n-1$ at $\alpha$ by
+
+$$
+P(t)=\sum_{k=0}^{n-1}\frac{f^{(k)}(\alpha)}{k!}(t-\alpha)^k
+$$
+
+Example:
+
+When $n=1$, $P(t)=f(\alpha)$.
+
+When $n=2$, $P(t)=f(\alpha)+f'(\alpha)(t-\alpha)$.
+
+When $n=3$, $P(t)=f(\alpha)+f'(\alpha)(t-\alpha)+\frac{f''(\alpha)}{2}(t-\alpha)^2$.
+
+**Key property:**
+
+$$
+P^{(k)}(\alpha)=f^{(k)}(\alpha)\quad \forall k=0,1,\cdots,n-1
+$$
+
+For each $\beta\in [a,b]$, there exists $x$ between $\alpha$ and $\beta$ such that
+
+$$
+f(\beta)=P(\beta)+\frac{f^{(n)}(x)}{n!}(\alpha-\beta)^n
+$$
+
+_On rudin, it is_
+
+$$
+f(\beta)=P(\beta)+\frac{f^{(n)}(x)}{n!}(\beta-\alpha)^n
+$$
+
+Proof:
+
+Let $M=\frac{f(\beta)-P(\beta)}{(\beta-\alpha)^n}$.
+
+So that $f(\beta)=P(\beta)+M(\beta-\alpha)^n$.
+
+Need to show that $n!M=f^{(n)}(x)$. for some $x\in (\alpha,\beta)$. Defined $g(t)=f(t)-P(t)-M(t-\alpha)^n$.
+
+By our choice of $M$, $g(\alpha)=g(\beta)=0$.
+
+$$
+g(t)=f(t)-P(t)-M(n(n-1)(n-2)\cdots(n-k+1)(t-\alpha)^{n-k})
+$$
+
+for $k=1,2,\cdots,n-1$. And when $k=n$, $g^{(n)}(t)=f^{(n)}(t)-0-M(n!)$.
+
+Need to show that $\exists x\in (\alpha,\beta)$ such that $g^{(n)}(x)=0$.
+
+By Mean Value Theorem, $\exists x_1\in (\alpha,\beta)$ such that $g'(x_1)=0$.
+
+By Mean Value Theorem, $\exists x_2\in (\alpha,x_1)$ such that $g''(x_2)=0$.
+
+By Mean Value Theorem, $\exists x_3\in (\alpha,x_2)$ such that $g^{(3)}(x_3)=0$.
+
+$\cdots$
+
+By Mean Value Theorem, $\exists x_n\in (\alpha,x_{n-1})$ such that $g^{(n)}(x_n)=0$.
+
+Since $g^{(n)}(\alpha)=0$ for $k=0,1,2,\cdots,n-1$, we can find $x_n\in (\alpha,x_{n-1})$ such that $g^{(n)}(x_n)=0$.
+
+EOP
+
+## Chapter 6: Riemann-Stieltjes Integral