Frequently Asked Questions

Given the nature of the online quarter, we've compiled a list of Frequently Asked Questions (FAQs) below. . This FAQ should give you a good idea of what to expect this quarter.

For more details, see the Syllabus or email the staff list at gili @


Is CS103/CS106B/MATH51 a hard prerequisite for this course? CS103 is a "soft" prerequisite for CS109 in that we hope that you have the requisite mathematical maturity—that is, the basics of set theory, familiarity with basic proof techniques, and ability to learn new math notation. CS106B, on the other hand, is a "hard" prerequisite, because we would like you to fully understand concepts like hash tables and recursion, and we expect you to be able to translate word problems into Python programs. We only require programming at the level of CS106B; many students take CS107 and CS109 concurrently. Math 51 is also a "hard" prerequisite because we expect you to know calculus (integration/differentiation) and linear algebra (basic operations on vectors and matrices). If you have seen multivariable calculus and are comfortable with the chain rule of calculus, you should be good on the calculus front.

Okay, I plan to take CS103, CS106B, and CS109 concurrently this quarter. Is this a good idea? This sounds like a LOT of work (both time-wise and concept-wise), but if you are up to the challenge....well, don't say we didn't warn you. Some students have succeeded taking a strict subset of these courses concurrently.


How do I attend live lecture? You must log in to Zoom through Canvas; you must log in to Zoom with your Stanford account. The Zoom link will be accessible through the course website and Canvas (which will be published soon).

Am I seriously going to have to sit through three 80-minute synchronous Zoom sessions a week? No. We are cutting down each lecture meeting to 50 minutes so we will meet MWF, 10:30AM-11:50AM Pacific. We are utilizing about 30 minutes of pre-recorded videos that cover introductory material for each lecture. You should watch and be familiar with this material prior to attending the live component, which is dedicated to interactive problem solving and advanced concept learning. To encourage lecture viewing in a timely manner and to ensure that you can effectively participate in these live sessions, we will have required, short self-tests on the pre-recorded content. These "concept checks" will count towards your grade.

What if I don't watch the pre-recorded lecture videos? Can I still come to class? Yes, absolutely. The concept checks are there to make sure you are familiar with the definitions and introductory material covered in the videos so that you can actively participate in the live lecture, where you may discuss problem solving techniques with other students in Breakout Rooms. If you learn better by skimming the Lecture Notes before class (as opposed to watching the short videos), great. You also have the opportunity to submit concept checks post-lecture (more details coming soon).

Will I have to complete Lecture 1's concept check before class on Monday 6/22? Lecture 1's pre-recorded content is intended to be watched after lecture; the Gradescope assignment (covering Lectures 1 and 2) will be posted after class, in the evening PT.

I can't make the live lecture times. Are lectures recorded? Yes. We realize that this is an online course, and many of you will have various constraints on your schedule due to timezones, family, jobs, etc. All Zoom recordings will be posted to Canvas shortly after lecture. However, we strongly encourage you to attend the live lecture times if you are able.

Tools and technology

There are so many software tools that I can't keep track! Where should I be?This website is your main resource for all of CS109. Start here and then go forth.

Help! I can't see the CS109 Canvas! How can I watch the pre-lecture videos/complete concept check for Lecture 1? Heyyy, high-five to you, rockstar, for getting a head start on the material! However, you do not have to prepare, watch, read, or complete anything prior to Lecture 1. Concept check for Lecture 1 and 2 (combined) will be officially published after lecture, as well as the videos on Canvas.

How fluent do I have to be in Python/LaTeX? There will be some programming problems on each problem set which must be completed in Python. We will hold several Python tutorial sessions throughout the quarter to familiarize you with the features of Python necessary for probability and statistics. LaTeX is a document preparation system that you are encouraged (but not required) to use when writing up your problem sets. We will provide a self-tutorial on getting started with LaTeX using an online LaTeX editor, Overleaf, or with a locally installed editor.

How will office hours work if I am in a different timezone?Our teaching staff is also global this quarter. We will try our best to hold office hours that fit students from different timezones.


Can I audit/shop this course? Can I audit this course? How do I get added to the Canvas?

We have turned on the "Shopping" option for this course (as per this VPTL guide to shopping courses off-campus). You will have access to all the videos/lectures through Canvas even if you are not enrolled. If you have issue accessing Canvas as an auditor throughout the quarter, please email course staff.

I will exceed 20 units this quarter. Will you sign my units petition? No.

Will this online version of the class be the same level of rigor and difficulty as a typical, regular quarter of CS109? As part of our learning goals, we aim to have this quarter give you the same level of intellectual rigor as we see during the normal academic year. The problem sets, lecture examples, section topics, and course concepts are as challenging and as in-depth as those covered in a regular quarter. However, we also recognize that many of you simply cannot prioritize academics during this global situation. We have adjusted the lecture schedule to reflect this change in learning environment.

Should I take CS109 this quarter because it will be easier? See our answer to the previous question.

Can I take this course for less than 5 units if I am an undergraduate? No. If you are an undergraduate, you must take this course for 5 units.