Notes, podcasts etc. from the lectures

Monday, August 19. Started with a mixture of sections 1.1 and 1.2. Introduced\(\sigma\)-algebras and probability measures and went through the results in Remark 1.2 and Section 1.2. Next time I shall return to Section 1.1 and the heavier results around the Monotone Class Theorem. Podcast. Notes from the lecture (in Norwegian).

Thursday, August 22. Continued lecturing on a mixture of sections 1.1 and 1.2. The only thing left now is the proof of the Monotone Class Theorem which I'll do on Monday. I'll not cover section 1.3 in class (it consists mainly of examples, some of which I'll done already), but will continue with sections 1.4 and 1.5. Podcast. Notes

Monday, August 26. I first finished the first two sections by proving the Monotone Class Theorem and continued by introducing conditional probabilities and proving Bayes Theorem. Finally, I introduced the (important!) notion of independence and showed by example that a pairwise independent set of events need not be independent. On Thursday, I'll start Chapter 2. Podcast, part 1. Podcast, part 2Notes

Thursday, August 29. Before the break, I went through Section 2.1 up to (and including) the definition of distribution functions, filling in some details along the way. After the break, I did a selection of this week's exercises: 1.5, 1.6, 1.8, 1.9, 1.16, and 1.18. Podcast. Notes.

Monday, September 2. The physical lecture was canceled, but I covered the material through podcacts. The first podcast deals with the results on page 41 and 42. The second covers the rest of Section 2.1 plus section 2.2 and 2.3.

Podcast, part 1, Notes, part 1.

Podcast, part 2 Notes, part 2.

Thursday, September 5. Went quickly through Section 2.4 and started Section 2.5 where I got to the bottom of page 55. After the break, I did a selection of this week's problems: 1.31, 1.34, 1.42, 1.44 and the beginning of 2.2. As there seemed to be interest in a full solution of exercise 2.2, I have made one available here. Podcast. Notes.

Monday, September 9. I started by proving Theorem 2.28. Then I went straight to section 3.1 to cover the expectation of a general stochastic variable while we still had Theorem 2.28 fresh in mind. I gave the definition of the expectation in the general case and proved theorem 3.4. Next time, I will first pick up a few bits and pieces from sections 2.5 and 2.6 before I continue with the (very important) Theorem 3.5. PodcastNotes.

Thursday, September 12. Went back to section 2.6 to pick up the definitions of moments, variance, and standard deviation, before I continued with Theorem 3.5 on the expectation of products of random variables and its corollary 3.6. After the break I did problems 2.11, 2.16, 2.17, and 2.20.  On Monday I shall continue with Section 3.2 (which I'll treat in a rather cursory fashion) and sections 3.3 and (the beginning of) 3.4. Notes. Podcast lecture. Podcast problems.

Monday, September 16. A most productive day! I first went quickly through Section 3.2, leaving the proof of Theorem 3.9 as self-study, and then continued with sections 3.3 and 3.4, following the book quite closely. This means that I have caught up with the schedule and will start Chapter 4 next time. Notes Podcast.

Thursday, September 19. Lectured on Section 4.1 up to and including Proposition 4.6. After the break I did exercises 3.3, 3.5, 3.4, and one half of 3.6 (in that order). If you thought they were tough, so did I! Notes. Podcast

Monday, September 23. I started the lecture with a little detour to sort out the relationship between \(\sum_{n=1}^{\infty}P(A_n)=\infty\) and \(\prod_{n=m}^{\infty}(1-P(A_n))=0\) that is needed in the proof of the second half of Borel-Cantelli's lemma. I then followed the book rather closely from Definition 4.8 up to and including Lemma 4.11. Notes. Podcast.

Thursday, September 26: Before the break, I lectured on the Monotone Convergence Theorem and Fatou's Lemma (and the corollary in-between). After the break, I did problems 2.40, 2.41, 2.43, and 2.50. Notes. Podcast. (For some reason, the microphone fell out for about a minute around 1.03).

Monday, September 30. Finished Chapter 4 by proving Theorem 4.18 (Dominated Convergence) and its corollaries and sketching the argument in Section 4.3. After the break I talked a little bit about different laws of large numbers and proved theorems 5.1 and 5.2. Next time I shall continue with section 5.4. Notes. Podcast of first half. Podcast from second half.

Thursday, October 3. Before the break, I covered section 5.4. After the break I did exercises, concentrating on the convergence in probability part of exercise 4.4, which is technically quite challenging. Notes. Podcast.

Monday, October 7. The physical lecture was canceled, but I covered the material through a podcast. I first finished Chapter 5 by covering sections 5.5 and 5.6. (In section 5.6, I also proved in detail that a random variable that is measurable with respect to the tail field \(\mathcal{F}_{\infty}^*\)is almost surely constant). I then started Chapter 6 by introducing complex valued random variables Z and their expectations E(Z). I also proved the important inequality |E(Z)| ≤ E(|Z|), which is just stated without proof in the book. Notes. Podcast.

Thursday, October 10: Before the break, I proved Theorem 6.3 and most of Theorem 6.4. After the break, I did problems 4.12b)c), 4.13, 4.23, and (most of)  4.28. Notes. Podcast.

Monday, October 14: Today I covered the rest of Section 6.1, inserting an informal explanation of the Fourier Inversion Theorem along the lines of these notes. Notes. Podcast.

Thursday, October 17: Before the break I lectured from Section 6.2, and made it halfway through the proof of Theorem 6.17 (I'll take the second half on Monday). After the break I tried to do problems 5.11 and 5.12, but the Smartboard acted up and I lost concentration towards the end. Notes. Podcast.

Monday, October 21: Completed section 6.2, including a survey (without proofs) of subsection 6.2.1. I hope to do most of the important Section 6.3 on Thursday. Notes. Podcast.

Thursday, October 24: Before the break I covered Section 6.3 on Lévy's Continuity Theorem. After the break I did problems 6.6 and 6.8. Notes. Podcast.

Monday, October 28: Initially we had some problems with the microphones and as the lecture started a little late, I didn't have time to cover all the material I had planned. Most of the time was spent on Section 6.4 and the Central Limit Theorem. I followed the approach in the book, but tried to make the ideas behind Lyapounov's theorem more transparent by structuring the proof differently. In the last ten minutes I covered Section 7.1, which means that I shall start with Section 7.4 next time. After that we move to Chapter 8. Notes. Podcast.

Thursday, October 31: Technical problems made the lecture a bit difficult, but I covered Section 7.4 before the break. After the break I did problems 6.9 and 6.11 and sketched two possible solutions of 6.12 (which seems hard to do completely rigorously with the methods we have available). Notes. There is a mysterious part of the podcast from minutes 8 to 12 when the Smartboard screen went black, but the screen on the wall still functioned. Podcast.

Monday, November 4: Covered all of Chapter 8, except Jensen's inequality for conditional expectations. Will say something about this on Thursday, but may not give the full proof. Notes. Podcast.

Thursday, November 7: I talked briefly about Jensen's inequality for conditional expectations (Theorem 8.7), before turning to Chapter 9 where I introduced martingales and sub- and supermartingales, and gave a few examples (essentially examples 1 and 3 on page 279). After the break, I did problems 6.29 and 6.34. Notes. Podcast.

Monday, November 11: Continued with Chapter 9. I first finished Section 9.1 by proving Proposition 9.6 and Theorem 9.7 (Doob Decomposition), before I continued with Section 9.2 and Theorems 9.8-9.11. I followed the exposition in the book, but tried to make the technical tools a bit more visible. Notes. Podcast.

Thursday, November 14: Before the break, I completed Section 9.2 by proving Theorem 9.12-9.18. After the break, I did problems 8.1 and (most of) 8.7. Unfortunately, the first part of the lecture (before the break) was rather messy with a lot of misprints and false starts, The second part (the problems) is better. Notes. Podcast.

Monday, November 18:  Before the break, I covered Section 9.3, but skipped the part on backward martingales. After the break, I started on Section 9.4 on uniform integrability where I made it to the statement (but not the proof) of the main theorem 9.28. Along the way I solved Exercise 9.14 which is a bit too important to be left along the roadside. Be aware that I made a notational error before the break: I used \(a\wedge b \) instead of \(a\vee b\) for the maximum of \(a \mbox{ and } b\) (this corrected in the notes, but not in the podcast). Except for the notation, everything is correct. Notes. Podcast.

Thursday, November 21: Rounded off the ordinary lectures by proving Theorem 9.28 and (most of) Theorem 9.31. Next week, I shall only be reviewing. After the break, I did problems 9.7, 9.8, and 9.9. Unfortunately, I did not have time for 9.10, and I may make a separate recording of it later. Notes. Podcast. Notes for problem 9.10. Podcast of problem 9.10.

Monday, November 25: Reviewed material about \(\sigma\)-algebras, filtrations, measures, expectations, distributions and modes of convergence. Will continue next time. Notes. Podcast.

Thursday, November 28: This was the last lecture, and I reviewed convergence theorems, limit theorems (laws of large numbers, central limit theorems), tail events, inequalities, and martingales. Notes. Podcast.

Published Aug. 19, 2019 2:29 PM - Last modified May 12, 2020 6:55 AM