Introduction to Analysis II¶
Notes for Introduction to Analysis II. The screenshots are from the lecture notes of Prof. MC Li.
- Introduction to Analysis II
- week 1-1 (3/3/2020)
- Week 1-2
- Week 1-3(3/5/2020)
- part 1 (pdf 32)
- Theorem 32.4 : continuity on a closed interval => integrability
- Theorem 32.5 (the Intergrability Theorem)
- Definition 32.6 (content zero and measure zero)
- Theorem 32.7 (contious except content zero implies integrability)
- Theorem 32.8 (the Riemann-Lebesgue theorem in one variable: Lebesgue’s criterion for Riemann-integrability)
- Week 2-1(03/10/2020)
- Week 2-2
- Week 2-3(2020/3/12)
- HW1
- Week 3-1
- Week 3-2
- Week 3-2
- Week 4-1
- Week 4-2
- Week 4-3 (X)
- Week 5-1 5-2
- The course turn online
- Week 9 - 2020/4/28 TA class
- Patition to 2 part need theorem
- Week 12(2020/5/20) - Self study for exam 2
- Ch40. - Inproper Integral I (S is not bounded)
- Ch 41. - Inproper Integral II (f(S) is not bounded)
- Ch 42. - Dirichlet's test / Absolute convergence / Cauchy principle value
- Ch 43. - Improper Integral on \(R^k\)
- Ch 44. - Lebesgue measure / Lebesgue measurable (Definition)(Key!)
- Ch 45. - Lebesgue Integral
- Ch 46. - Riemann-Stieltjes integral
- Ch 47-48
- Review of FTC
- Ch 49. - Green's theorem(2D proj.)
- Ch 50-51. - Surface Area and Surface Integral
- Ch 52. - Vector derivatives
- Ch 53. Gauss' Divergence Theorem
- Ch 54. Stroke's Theorem
- Ch 55-56. Higher Dimension
- Week 12 - Exam 2
- Week 15 - for exam 3
- Week 15 - Series
- Week 15 - Sequence of functions
- Sery of function
week 1-1 (3/3/2020)¶
Reimann Intergral¶
partition and refinement¶
- refinement = add points to partition
- definition of Reimann sum (\(U_f(P), L_f(P), R_f(P)\))
- show \(L_f(P) \le L_f(Q)\) and \(U_f(P) \ge U_f(Q)\)
- hint : \(Q = P \cup (Q-P)\)
- Reimann intergral
- Reimann intergrability :::info Proof of Prop. 31.3
31.3.1 since f is \(bounded\), by the \(completeness\) of \(R\), \(m_i \le f(x_i) \le M_i\) are all well defined.
31.3.2
:::
Week 1-2¶
Reimann Intergrability¶
- http://home.iitk.ac.in/~psraj/mth101/lecture_notes/lecture15-16.pdf
- inf and suf and reimann intergral definition
refinement¶
Note: proof of equivalence part use the property of inf and sup
boundedness and monotonicity => integrability¶
- P = \(\{a=x_0<x_1<...<x_n=b\}\) where \(x_i = a+i\frac{b-a}{n}\)
- \(U_f(P) - L_f(P) = \frac{b-a}{n}[f(b)-f(a)]\)
- Q.E.D
- end of class
Week 1-3(3/5/2020)¶
part 1 (pdf 32)¶
Theorem 32.4 : continuity on a closed interval => integrability¶
- closed and bounded on \(R\) \(\implies\) compact
- teacher hint : continuity and compact relation
- review: compact - f(cont.) -> compact
- not used here
- Theorem 11.3 says f is continuous on a compact space then it is uniformly continuous
- \(f\) is \(uniformly\ continuous\) on \([a, b]\)
- the left is trivial
- let P be a partition with \(|x_{i+1}-x_i|\lt\delta\)
- then \(M_i-m_i \le \epsilon\ \forall i\) by uniform continuouity
- (actually) \(\forall \epsilon\ \exists \delta\)
- then \(U_f(P) - L_f(P) = \sum (M_i-m_i)*(x_i-x_{i-1})\)
- \(\le \epsilon \sum (x_i-x_{i-1})\)
- \(= \epsilon (b-a)\)
- then for more formal proof replace \(\epsilon\) with \(\frac{\epsilon}{3*(b-a)}\)
- \(Q.E.D.\)
Theorem 32.5 (the Intergrability Theorem)¶
- \(If\ f\ :\ [a, b]\rightarrow\mathbb{R}\ be\ continous\ at\ all\ except\ finite\ many\ points\ in\ [a,b]\)
- \(then\ f\ is\ Reimann\ integrable\ on\ [a,b]\)
- proof:
- key idea : remove not continous points
- let M, m be global \(suf\) \(inf\)
- reduce to \(((M-m)+(b-a))*\epsilon\)
- To review, when will \(Min, Max\) exist
- compact in \(\mathbb{R}\), closed and bounded
- idea : proof \(I\) bounded + \(sup/inf \in I\)?
Definition 32.6 (content zero and measure zero)¶
- see pdf definition
- show \(\{\frac{1}{n}\mid n\in\mathbb{N}\}\) is content zero
- only finite elements out of \(epsilon\) range
- show Q is measure zero
- show that length of \({\bigcup^{\infty}_{0}}I_i\) is finite(by \(\epsilon(1+\frac{1}{2}+\frac{1}{4}+...)\) trick
Theorem 32.7 (contious except content zero implies integrability)¶
- similar method with 32.5
- sketch of proof
- try to remove the points like we did in Theorem 32.5
- use definition of content zero
- show \([a,b]-{\bigcup^{k}_{0}}I_i\) is compact by removing boundary of \(I_i\)
Theorem 32.8 (the Riemann-Lebesgue theorem in one variable: Lebesgue’s criterion for Riemann-integrability)¶
- mentioned, will cover if have time
- Theorem 32.9 : my guess by substraction and 32.5
- Theorem 33.1 (the fundamental theorem of calculus)
Week 2-1(03/10/2020)¶
Theorem 33.1 (the fundamental theorem of calculus)¶
- part1
- proof sketch:
- Riemann integrable \(\implies\) bounded on \([a,b]\)
- \(\exists M > 0 \ni |f(t)| \le M \forall t \in (a,b)\)
- then uniform continuity on \([a, b]\) is trivial
- \(\forall x,y \in [a,b] \ni |x-y|<\delta\)
- \(|\int_{a}^{x}f(t)dt - \int_{a}^{y}f(t)dt| \le M*\delta\)
- \(\epsilon - \delta\) trick, M is constant
- def of f continuous
- \(for\ x \in [a,b] \ni x > x_0\)
- express \(f(x_0)\) as \(f(x_0)\frac{\int_{x0}^{x}1dt}{x-x_0} = \frac{\int_{x0}^{x}f(x_0)dt}{x-x_0}\)
- we have \(\frac{\int_{a}^{x}f(t)dt - \int_{a}^{x0}f(t)dt}{x-x_0} - f(x_0) = \frac{\int_{a}^{x}f(t)dt - \int_{a}^{x0}f(t)dt}{x-x_0} - \frac{\int_{x0}^{x}f(x_0)dt}{x-x_0}\)
- thus if \(x \in [a,b] \ni x_0<x<x_0+\delta\)
- then \(|\frac{\int_{a}^{x}f(t)dt - \int_{a}^{x0}f(t)dt}{x-x_0} - \frac{\int_{x0}^{x}f(x_0)dt}{x-x_0}| = |\frac{\int_{x_0}^{x}f(t)-f(x_0)dt}{x-x_0}| \le \frac{\int_{x_0}^{x}|f(t)-f(x_0)|dt}{|x-x_0|}\)
- since f is continuous
- \(\frac{\int_{x_0}^{x}|f(t)-f(x_0)|dt}{|x-x_0|} < \frac{\int_{x_0}^{x} \epsilon dt}{x-x_0} = \epsilon\)
- \(x < x_0\) case can be done similarly
- above proves \(\(\frac{d}{dt}(\int_{a}^{x}f(t)dt)\mid_{x=x_0} = f(x_0)\ \forall x_0\ at\ which\ f\ is\ continous\)\)
- part2 : \(\int_{a}^{b}f(t)dt = F(b)-F(a)\)
- proof sketch:
- by def \(\forall \epsilon \exists\ partition\ P \ni U_f(P)-L_f(P) < \epsilon\)
- make a refinement Q of P to exlude finite indifferentiable points
- apply MVT(mean value theorem) to intervals
- \(F(b)-F(a) = \sum F(x_i)-F(x_{i-1})\)
- = \(\sum F^{'}(t_i)(x_i-x_{i-1})\)
- = \(\sum f(t_i)(x_i-x_{i-1})\)
- \(L_f(Q) \le F(b)-F(a) \le U_f(Q)\)
- \(L_f(P) \le \int_{a}^{b}f(t)dt \le U_f(P)\)
- then \(|\int_{a}^{b}f(t)dt-(F(b)-F(a))| < \epsilon\)
Week 2-2¶
- pass
the Generalized Mean Value Theorem for Integrals¶
Integration by parts¶
advanced practice problem¶
Week 2-3(2020/3/12)¶
Several variables¶
- rectangle
- def is similar with 2d rectangle partition
- for general bounded region
- for such S, use rectangle "disk" \(D\supseteq S\) + characteristic function \(\chi_S(x, y)\)
- def characteristic function \(\chi_S(x, y) : \mathbb{R}^2 \rightarrow \{0,1\}\)
- then can define \(\iint_SfdA = \iint_D(f_{\chi _S})dA\)
- fact : \(S1 \cup S2\) is Reimann intergrable doesnt \(\implies\) \(S1\ and\ S2\) are
- consider s1 + s2 = 0
Jordan Measurable sets and Riemann Intergrability¶
content zero and Jordan measurable sets¶
content zero¶
- bounded and \(\subset \mathbb{R}^k\)
- if for any \(\epsilon\) > 0 there exists a finite collection of k-dimensional rectangular boxes \(D_1, D_2, ..., D_n \ni Z \subseteq \cup_{i=1}^{n}D_i\) and \(\sum volume(D_i)<\epsilon\)
! Jordan measurable¶
- A bounded set \(S \subset \mathbb{R}\)
- \(\mathbb{\delta} S\) is content zero
Case study¶
consider \(\mathbb{Q}\) / Cantor Set / Fat Cantor Set / set bounded by Sierpinski Curve all of them are not Jordan measurable
continuity except content zero implies Riemann integrability on a rectangle¶
sufficient conditions for content zero¶
- set relationship
- subset => ok
- finite union => ok
- countable union => content X, measure V
- let \(f : (a,b)\rightarrow \mathbb{R}^2\ be\ C^1\ function\)
-
\(f([c,d])\) is content zero when \([c,d] \in (a,b)\) ::: info \(C^1 \implies M = max\{|f'(x)| \mid x \in [c,d]\}\) exists let \(\epsilon>0\), Take \(n \in \mathbb{N} \ni \frac{?}{n} \lt \epsilon\) partition [c, d] to n equal-length parts let \(f = (f_1,f_2)\), by MVT to \(f_1\) and \(f_2\) \(|f_k(x)-f_k(x_i)| \le M*(x_{i}-x) \forall x \in [x_{i-1}, x]\) \(|f_k(x)-f_k(x_i)| \le M*\frac{d-c}{n}\) Hence \(f([x_{i-1},x_i])\) is contained in the rectangle \(D_i\) centered at \(\vec{f(x_i)}\) with side length \(\frac{2M(d-c)}{n}\) then volume of cover is \((\frac{2M(d-c)}{n})^2*n \lt \epsilon\) :::
-
case for \(C^0\) not holds
- Peano Curve : \(C^0(\mathbb{R}, \mathbb{R}^2)\)
- Cantor function restrictedto the Cantor set of measure zero
sufficient conditions for Riemann integrability on a bounded region¶
zero Riemann integral and its corollaries¶
Inter and Outer Areas¶
HW1¶
Reference¶
My part - Theorem 32.7 - Continuity except content zero -> intergrability¶
:::info proof: by the definition of content zero proof by content zero intergral = 0 not the cutting technique \(\int_{[a,b]}f = \int_{S}f + \int_{S^{'}}f\) where \(S^{'}\) is the content zero part proof each part of S' is intergrable and sum of them abs <= 0 , hint : use \(max(|M|, |m|)\epsilon\) => \(\int_{[a,b]}f\) is well defined Q.E.D. :::
:::spoiler the picture solution is not that correct should deal with closed interval more carefully and use \(max(|M|, |m|)\epsilon\) to proof eq 0 :::
Week 3-1¶
Practice Class¶
! 35.4 sufficient conditions for Riemann integrability on a bounded region¶
- union of 2 content zero is content zero
- the discontinuous parts are \(\delta S\) and \(Z\) so \(D\) is still intergrable
35.5 zero Reimann intergral¶
content zero and f bounded => intergrable and intergral = 0
- end of class
Week 3-2¶
Inner Area and Outer Area¶
- concept : lattice
!Theorem 33.3 norm Partition can bound difference to U, L, R¶
- will be useful for future proof
- \(\forall \epsilon >0 \exists \delta > 0\) s.t. if P is a partition with \(norm( P ) < \delta\), \(max\{|\int_a^bf(x)dx - R_f(P)|, \int_a^bf(x)dx - U_f(P)|, \int_a^bf(x)dx - L_f(P)|\} < \epsilon\)
- proof sketch(U part)
- by theorem 32.1 equivalent condition for Riemann integrability
- => get a partition \(Q\) s.t. \(U-L < \frac{\epsilon}{2}\)
- let the norm-limited partition be \(P\)
- \(\lambda\) for \(P\) can be generated from \(\epsilon\) and \(|Q|\)
- key
- refer to P's refinement \(P\cup Q\), and the fact that \(|Q|\) is finitely given by \(\epsilon\)
- see \(P\cup Q\) as \(Q\) injected to \(P\)
- make \(\delta\) bounded by \(\frac{\epsilon}{4*M*|Q|}\)(teacher's version) or \(\frac{\epsilon}{2*(M-m)*|Q|}\)
- \(U_f(P) - U_f(P\cup Q) \le (M-m)\delta*|Q|\)
- \(U_f(P) \le U_f(P\cup Q) + \frac{\epsilon}{2}\)
- \(U_f(P) \le \int_a^bf(x)dx + \frac{\epsilon}{2} + \frac{\epsilon}{2}\)
- by choice of \(Q\) and \(P\cup Q\) is refinement
- \(U_f(P) \ge \int_a^bf(x)dx - \epsilon\) by definition of intergral
- \(|\int_a^bf(x)dx - U_f(P)| \le \epsilon\)
Week 3-2¶
MVTs¶
Theorem 36.1¶
- proof sketch:
- f is continuouson S and S compact
- Extreme Value Theorem => Max and Min Exists
- i.e. \(\exists p, q \in S \ni f(p) = sup, f(q) = inf\)
- https://en.wikipedia.org/wiki/Extreme_value_theorem
- see the generalized version
- \(mg(x) \le f(x)g(x) \le Mg(x)\)
- since both f and g are continuous on S and S is Jordan measurable
- so \(m\int_Sg(x)d^kx \le \int_S f(x)g(x)d^kx \le M\int_Sg(x)d^kx)\)
- if \(\int_Sg(x)d^kx = 0\) always hold, take any \(c \in S\)
- else by corollary 10.4 (IVT for several variables)
- S is connected, f is continous on S
- \(m \le \frac{\int_S f(x)g(x)d^kx}{\int_S g(x)d^kx} \le M\)
Iterated Intergral and Funini's Theorem¶
definition of iterated intergrals¶
Week 4-1¶
IIS meeting => not attended
Week 4-2¶
Change of Valriables¶
Lebesgue's Criterion for integrablility(go back)¶
::: success - definition of oscillation of f of an interval/at a point x - \(\omega f(I) = sup\{|f(a)-f(b)|:a,b\in I\}\) - \(\omega _f(x) = inf\{\omega f(B(x, \delta)):\delta>0\}\) - trivial to see \(\omega _f(x)=0\) when f is continuous - exercise :::
::: info (integrable => measure 0 discontinuous points) - let discontinuous set be \(D\) - let \(N(\alpha) = \{x\in[a,b] : \omega f(x) \ge \alpha\}\) - since \(D = \cup_{k=1}^{\infty}N(\frac{1}{k})\) - the left is to proof \(N(\alpha)\) is \(measure\ zero\) - then by integrability for \(\alpha\) exist partition that \(diff \le \alpha\epsilon/2\) - done by definition of \(N(\alpha)\) - can show \(len(N(\alpha)) \lt \epsilon\) (integrable <= measure 0 discontinuous points) - let discontinuous set be D - let \(\epsilon = len(D)\) - let - devide into two parts - E, \(\omega f(J) >= \epsilon\) - still measure zero by subset - compact by closed and bounded - K = [a, b]\E, \(\omega f(J) < \epsilon\) - compact - both part is compact - => has finite subcover - by \(len(E) < \epsilon\) and \(\omega f(K) < \epsilon\)
:::
Week 4-3 (X)¶
Week 5-1 5-2¶
Change of Variables¶
Theorem 39.1¶
- part2 proof - \(\forall\ \bar{x} \in S,\ \exists\ r > 0 \ni B_r(\bar{x}) \subset S\) - \(h_i = (0, ... ,|h_i|, ...0)\) s.t. \(h_i < r\) - for each \(y \in T\), \(f(x, y)\) is \(C^1\), apply MVT - \(\exists t_i \ni f(\bar{x}+h, y) - f(\bar{x},y) = \nabla f(\bar{x}+t_ih,y)h\) - uniform continuity of \(\frac{\partial f(x, y)}{\partial x_i}\) on \(\bar{B_r(\bar{x})} \times T\)
39.2¶
- proof, apply chain rule directly, y is i.d. variable, view as constant
39.3 the bounded convergence theorem(wait, graduate level class content)¶
39.4¶
- apply 39.3
ch 40, 41 Improper Itergral¶
- Type 1 : infinity
- Type 2 : undefined
- tests:
- comparison test
The course turn online¶
Week 9 - 2020/4/28 TA class¶
proof of 42.1¶
- link
- MVT-2 of integral
Patition to 2 part need theorem¶
Week 12(2020/5/20) - Self study for exam 2¶
Ch40. - Inproper Integral I (S is not bounded)¶
- Inproper Integral I (S is not bounded)
- comparison test
- 40.2 proof sketch:
- two part(g>=f and limitied)
- 40.3 use definition of limit
- poly functions
- by direct calculation
- Care:
- condition, >0
Ch 41. - Inproper Integral II (f(S) is not bounded)¶
- Inproper Integral II (f(S) is not bounded)
- silmilar to 40
- Care:
- different conclusion on \(cx^{-p}\) at x -> 0
Ch 42. - Dirichlet's test / Absolute convergence / Cauchy principle value¶
- 42.1 Dirichlet's test for improper integral
- bounded and decay to 0
- 42.2 Define improper integral to Complex number
- absolute convergence for C
- \(\sqrt{Re^2 + Im^2}\)
- absolute convergence for C
- 42.3 Absolute convergence implies convergence
- counter example for opposite direction
- sinx/x
- counter example for opposite direction
- 42.4 Cauchy principle value (P.V.) definition
- \(+- \infty\)
- \(|f(x->c)| = \infty\) and want \([a,c) \cup (c,b]\)
- 42.5 how to use
- If improper integral is convergent, P.V. = its value
- It's possible that improper integral is convergent but P.V. is not
- 42.6
- Let a < 0 < b and f ∶ [a,b] → R be continuous on [a,b] and differentiable at 0,
- then P.V.∫baf(x)/xdx exists
Ch 43. - Improper Integral on \(R^k\)¶
- 43.1 Limit indeppendent of choice of \(K_n\)
- may converge or diverge(only has case \(+\infty\))
- 43.2 Definition
- 43.1 shows 43.2 well-defined
- 43.3 Higher order 1/|x|^p
- evaluation of function with no anti-derirative by higher dimension improper intergral + fubini
Ch 44. - Lebesgue measure / Lebesgue measurable (Definition)(Key!)¶
- Key: cut in range not domain
- Key: Preimage, Tiled
- Key: closed/open/general/for Rk
- Key: Countable(seq of)
- See as a extension of Jordan measurable
- Jordan measurable - Reimann Integrability <=> Lebesgue measurable - Lebesgue Integrability
- Review of Jorndan Measurable
Lebesgue measurable but not Jordan measurable¶
Review of Jorndan Measurable¶
- Note: Riemann-Lebesgue Theorem
Ch 45. - Lebesgue Integral¶
- define on function
- if for all integral I, pre-image(I) is L.M.
- continous => f is lebesgue measurable
- (similar to ) bounded convergence theorem (\(\forall x, f(x) = lim f_i(x)\))
45.5.2 Comment is important for complete understanding¶
- https://drive.google.com/file/d/1-YLPdabFXtcVg3-nxqRzJbtVwzWPYGEN/view
- around 45:00
banach tarski paradox(supplement)¶
- search => related to A.C. (Axiom of Choice)
Ch 46. - Riemann-Stieltjes integral¶
- Noun: finer(is improvement of)
- Key Concept: S(f, g, P)
- EQ criterien (similar to R.I.)
- cases (Step function, Bounded Variant)
- intergrant f , inegrator g, partition P, dummy variable x
Ch 47-48¶
Arc Length / Work¶
- C1 curve (vector-valued function)
- dr = dg'(t), ds = d|g'(x)|
Line Integral / Work¶
- real function \(f : U \supset C \to R~and~C1 curve C\)
- \(U~open\)
- \(C\subset U\subset R^k\)
- \(f:U \to R continous\)
- vector function f
- field f
- use dot product
differential form (a way to write work??)¶
- Q
Rectifiable (48.4)¶
- contious, not necissarily injective
- define on C1 curve, Reiemann similar sum + sup
- proof https://drive.google.com/file/d/1UzJXLamXOVOZJ_bJlGczmPjAc9w7DhLi/view
Review of FTC¶
Ch 49. - Green's theorem(2D proj.)¶
- regular region
- is its interior's closure
- i.e. remove single point
- is its interior's closure
- simple closed curve
- piecewise smooth boundary with positive orientation(D on the left)
Use Green's to proof corollaries¶
- \(e^{i\pi}\) rotation or (-b, a) of g => (-Q, P)
convervative filed¶
- g is C2
- gradient of g is f
- results
proof of greens (Case)¶
https://drive.google.com/file/d/1N1tIY2vqZo4K9mbXG6-wf6WlJKmjP_aP/view?pli=1
Ch 50-51. - Surface Area and Surface Integral¶
Area¶
- D->E
- cross dg(x,y)dx dg(x,y)dy (D1)
- special case of g(x,y) = (x,y,h(x))
Integral¶
- integral>
- f: D->E->Real
Vector-valued¶
- orientation of E
- n
- physic meaning : flux
Ch 52. - Vector derivatives¶
- gradient
- apply for each dimension
- curl
- cross
- divergence
- dot
- laplace
- propositions
Ch 53. Gauss' Divergence Theorem¶
- jordan measurable for low to high dimension
- remark: divergence can be given a phiysic meaning by small ball and divergence theorem
Ch 54. Stroke's Theorem¶
- cosistent positive orientatio
- Right Hand Princile
Ch 55-56. Higher Dimension¶
- skip
Week 12 - Exam 2¶
Week 15 - for exam 3¶
Week 15 - Series¶
- https://www.math.ucdavis.edu/~hunter/intro_analysis_pdf/ch4.pdf
Definition of Convergence¶
- definition is always important
Cauchy Criterien¶
- a nice eq form
linearity of c. series¶
Absolute convergence(a.c.) and a+, a-¶
- introduce a+, a-
Comparison Test / Ratio Test / Root Test (for a.c.)¶
- comparison
- ratio/root is to compare to geometric seq
Raabe’s test¶
Test Conclusion¶
Conditional convergence c.c.¶
Alternating sequence¶
- convergence to 0 if
- decreasing
- alternating
- a_n to 0 b
Dirichlet’s test¶
- bi be a bounded above complex sery
- ai be a decrease to 0 sery
- aibi is c.
Abel’s test¶
- bi be a c. sery
- ai be a decrease to 0 sery
- aibi is c.
Rearrangement¶
- definition
- bijection of indices
- magic!
- Note: Q, the statement that not abs convegent is not formal
- i.e. why \(a^+, a^-\), one diverge another dont => diverge
Rearrangement of a.c. series¶
- prove by \(sup(\sigma^{-1}(\{1...n\}))\) exist as m
- use this + cauchy
Rearrangement of c.c. series¶
- any sum
Double Series!!!¶
- define absolute convergence of double series
- by an ordering is a.c.
- if a.c.(an ordering is )
- a.c. <=> all ordering is a.c.
- a.c. <=> iterated sum is a.c.
- if not a.c. ( a+, a- discussion)
- \(a+ = \infty, a- \lt \infty\)
- diverge to \(\infty\)
- \(a+ = \infty, a- = \infty\)
- various ordering can converge to any real number
- my proof(by expand to 1 d, use + - part to make S(if cannot => c.), and \(\sigma^{-1}\) can find k to dominate 0,0 to N,N)
- various ordering can converge to any real number
- \(a+ = \infty, a- \lt \infty\)
Product of a.c. series is a.c.¶
Cauchy Product¶
- ai, bi c. to A, B
- if one of ai, bi is a.c.
- Cauchy product is c. with sum AB
- else
- Cauchy product may d.
Week 15 - Sequence of functions¶
pt. uni. uni cauchy.¶
eq def of uni. conv¶
uni + cont. => target cont.¶
- lim f uni and all fn cont. => cont.
- cont. [] for all delta for above => () f cont.
Weierstrass approximation¶
- cont. has poly seq uni. approx
- http://www.math.univ-toulouse.fr/~lassere/pdf/2012INPsuitesD1bis.pdf
Dini's¶
- for each x , fx is bounded monotone
- x to lim f x is well defined and cont.
- then lim f is uni approx
Sery of function¶
- pt.
- abs.
- uni.
cauchy for uni conv¶
condition of swapping¶
- limit and int/de
- R.I. uni.
- fn pt. C1, fn' uni.
- seri
- same
Hint of final¶
- one mutant one time proof (1/2)
abel
Arzela-Ascoli theorem, the Heine-Borel theorem for functional spaces
S compact C0 F closed bounded uni equconti