Archives For mathematics

Several weeks ago, links to a survey article by Jeffrey Lagarias about Euler’s work and its modern developments and a blog post by Richard J. Lipton that discusses Lagarias’ paper were circulated on Google+. I’d like to thank Luiz Guzman and Joerg Fliege for first bringing these items to my attention.

Lagarias’ paper is full of lots of yummy goodies, but my favorite part is his summary of Euler’s approach to research (see Section 2.6 of the paper or the end of Lipton’s post).

Euler’s Research Rules

Taken directly from the paper, here is Lagarias’ summary of Euler’s research rules.

  1. Always attack a special problem. If possible solve the special problem in a way that leads to a general method.
  2. Read and digest every earlier attempts at a theory of the phenomenon in question.
  3. Let a key problem solved be a father to a key problem posed. The new problem finds its place on the structure provided by the solution of the old; its solution in turn will provide further structure.
  4. If two special problems solved seem cognate to each other, try to unite them in a general scheme. To do so, set aside the differences, and try to build a structure on the common features.
  5. Never rest content with an imperfect or incomplete argument. If you cannot complete and perfect it yourself, lay bare its flaws for others to see.
  6. Never abandon a problem you have solved. There are always better ways. Keep searching for them, for they lead to a fuller understanding. While broadening, deepen and simplify.

Lipton’s blog post also lists “Euler’s Research Rules.” My main motivation for reposting them here is to remind myself to follow them!

Talk: Proofs without Words

September 30, 2013 — 2 Comments

On Friday, September 20, I gave a 30-minute talk titled “Proofs without Words” during NAU’s Friday Afternoon Undergraduate Mathematics Seminar (FAMUS). As the name of the seminar suggests, the target audience for FAMUS is undergraduates. I usually give a couple talks at FAMUS each semester and this was my first of the semester. Here is the abstract with words for my talk.

In this FAMUS talk, we’ll explore several cool mathematical theorems from a visual perspective.

The talk basically went like this. I displayed a figure or drawing and then the goal was for the audience to come up with the corresponding theorem. I had a ton of fun and the audience seemed to enjoy it. The initial idea for the talk came from the book Charming Proofs: A Journey into Elegant Mathematics by Claudi Alsina and Roger B. Nelsen. This is a wonderful book that incorporates lots of visual proofs. If you don’t have a copy, I highly recommend it. I borrowed lots of ideas from it when I taught a class titled “Introduction to Formal Mathematics” while I was at Plymouth State University.

My original plan was to recreate a lot of the figures I had in mind using TikZ, but I should have known that I wouldn’t have time for that. When I was brainstorming the talk a couple days before, I decided to do a Google search in the hope that I could find some figures to borrow that others had already made. In my search, I stumbled on several references to “proof without words”, which is what I ultimately named my talk. In fact, there is a Wikipedia entry and Roger B. Nelsen also wrote a book called Proofs without Words: Exercises in Visual Thinking. Moreover, I was thrilled to find lots of cool figures on the Internet. For my talk, I borrowed images and content from the following sources:

In the end, my slides ended up being a sample each of these three sources. If you are ready to see some cool figures, check out the slides below. I’ve left the pauses in so that you can ponder the theorem before you see it.

As anticipated, I had more figures than I had time to discuss, but we did get through most of them.

The custom at FAMUS is to interview a faculty member after the 30 minute talk. The usual FAMUS host, Jeff Rushall, was out of town, so I was filling in for him. I had the honor of interviewing Michael Falk. This was fun for me because Mike was my masters thesis advisor.

This past Thursday was the first day of student presentations in my calculus class. It went awesome! The plan is to spend one whole class period each week having students present and discuss problems. The remaining three classes each week will be predominately spent on direct instruction and some small group work. I was emotionally prepared for a crash and burn session as it is often the case that the first day of student presentations in my calculus classes can be a bit rough. I’m totally okay with this as it always improves. But Thursday didn’t leave much room for improvement.

Class started by me asking for volunteers to present their proposed solutions to the problems from their Weekly Homework assignments. I anticipated being met with silence while students stared at their desks. The plan was to then gently nudge people to present. Instead, I had more people volunteer than we had problems. That wasn’t a problem I was expecting. I think I have a good group of students, so I maybe I had nothing to do with this. However, I am suspicious that the heavy marketing that I did helped a lot. Also, I’m curious how much my Achievement Points experiment played into the number of volunteers. Whatever the case, the students were ready to rumble.

In case you are interested, here is the general format for student presentation days, which will typically occur on Thursdays. A few days before the students are to present, I assign a Weekly Homework assignment. You can find the first one that the students did by going here (it’s not terribly exciting). For the most part, the problems on the Weekly Homework assignments are a subset of the material covered the previous week. I’m a big fan of having the students circle back on concepts as much as possible. The students also have Daily Homework assignments that consist almost entirely of problems from WeBWorK.

When the students arrive to class on presentation days, they are supposed to have completed or done their best to complete all of the problems from the Weekly Homework. Upon entering the room, students should grab a colored felt tip pen. I have a box of pens in a variety of colors. The students love the sky blue and purple ones and hardly anyone ever chooses the red ones. During class students can annotate their work only with their felt tip pen. My approach to this is nearly identical to what is described in my Math Ed Matters post located here. The big picture is that I want students to be able to process what they have on their paper as other students are presenting. However, I also want to make sure that I know what work students had done before they entered the room.

One difference between what I describe in the Math Ed Matters post is how I grade the homework that students are presenting problems from. In my other classes where presentations play a more prominent role, the students are presenting problems from their Daily Homework and it is these problems that they annotate with the felt tip pens. In this case, I grade the Daily Homework with a $\checkmark-$, $\checkmark$, $\checkmark+$ system. But in my calculus class, since the students are presenting problems from their Weekly Homework, the students are annotating these problems. Moreover, since students are revisiting topics from the previous week, I feel comfortable weighting the Weekly Homework in calculus more and grading it harshly.

There is no penalty for students using the felt tip pen and I encourage them to annotate to their heart’s content. However, when grading the assignment, the annotations are more or less ignored. That is, they are graded on the work they had done before class. The students need some coaching with how to use the felt tip pen, but they seem to dig it.

At the beginning of class, I usually write down all the problems that I’d like to see presented and then I ask for volunteers. In the case that more than one person wants to present a particular problem, the student with the fewest presentations has priority. If there is no priority, I try to choose one of the volunteers at random.

Depending on the number of problems and their difficulty, I will either have the students all come to the board at once to write down their solution while I bounce around the room answering questions or we’ll have one student come to the board at a time to present their proposed solution. In the first case, after the solutions are on the board, we will discuss each problem. In most cases, I’ll have the student that wrote down their proposed solution lead a discussion with the whole class about the problem and their solution.

Here is where my approach likely differs from many others. I don’t want all the solutions to be correct. I’d rather have students make mistakes. Ideally, I’d like to see a mixture of correct answers, answers with small mistakes, and answers with huge errors. It’s not that I want students to screw up. What I want is to have something to talk about. One of the greatest advantages of doing student presentations is that the audience should take on the role of skeptic. This makes the student engage with the material in a much different way than if they watch me. I’m an authority and usually the students just believe everything I say. I encourage the students to be willing to share what they have. It’s a low stakes endeavor for them. Just being willing to present is what they get credit for. (This is different in my upper-level proof-based courses.) On the other hand, I don’t want students to present total crap either.

This semester I have 48 students enrolled in calculus. I’d prefer a smaller class, but I can make it work. The goal is to get as many students to the board as possible. On Thursday, 9 students presented. I’m always concerned about how many students in class are engaged on presentation days. However, I’m confident that it is many orders of magnitude more than when I lecture (and I like lecturing and I think the students like it, too).

On Thursday, most of the solutions where flawless, but we also had a few that led to excellent discussions. In each of these cases, the presenters did a good job at fielding questions and comments from the audience and from me. This works because I make it a point to develop a community of trust. The audience has to behave appropriately. I encourage students to clap after each presenter and they clapped loudest after the two students that were at the board the longest due to flawed solutions. One of these students had told me before class that she did not understand function transformations (last week we were still reviewing precalculus). I encouraged her to volunteer for a problem related to function transformations, so that she could show us what we had. Indeed, she did have some misunderstanding, but in my view, this was the most beneficial presentation.

The fall semester starts in a couple days and I’ll be teaching Calculus 1 (for like the 15th time) and our undergraduate Abstract Algebra course. Despite my relatively low teaching load, I’ll also be advising 3 undergraduate research students (on two different projects) and 2 masters thesis students. Combined with the fact that I’m still frantically trying to prepare brand new IBL materials for my Abstract Algebra class, I expect a very busy semester. For this reason, I decided not to mess with the format of my calculus class very much. I think it has room for improvement—namely ramping up the IBL aspect of the course—but this will have to wait until a later semester. I feel a little guilty about this, but I’m no use to anyone if I’m trying to do too much.

Notice that I said that I wouldn’t mess with the format “very much.” I am going to make some small changes. In previous semesters, I always devoted one class period a week to students presenting problems at the board. This has always worked well for me, but last semester I tried something else that I don’t think was as successful. So, I’ve decided that I’ll return to presentation days. In the past, I had a fairly nebulous way of assessing student presentations. I want to encourage students to present, so I make it worth something. But on the other hand, I don’t want it to be a high stakes thing. A class typically benefits more from the discussion surrounding a less than perfect solution to a problem than they do from a presentation that is flawless. So, I encourage students to share what they have. Of course, I don’t want students putting crap up on the board on a regular basis either. In a small class, this isn’t very hard to manage, but in a class with 45 students (which is what I currently have enrolled in my calculus class), it gets a little trickier. I’ve been thinking about how to manage this for a few weeks.

The latest version of WeBWorK—which we use for our online homework platform—has a new feature called “Achievements.” You can read more about this here. This basic idea is this:

Instructors now have the ability to create and award “Math Achievements” and “Math Levels” to students for solving homework problems and for practicing good WeBWorK behavior. In a nutshell, students can earn achievements by meeting preset goals. For example, they might earn an achievement for solving 3 homework problems in a row without any incorrect submissions, or for solving a problem after taking an 8 hour break. Earning achievements and solving problems earns students points and after a student gets enough points they will be given a new “Math Level”.

I have zero experience with the WeBWorK Achievements, but I thought I would give it a try. I don’t want to make earning them mandatory and I don’t want to offer extra credit either. So, I’ve been passively brainstorming how to handle them.

Northern Arizona University now requires faculty to take daily attendance in all freshman-level courses. However, how we take this data into account is up the instructor. It just has to count for something. The past couple semesters, I’ve been diligent about taking attendance, but I’ve always been a little bit vague about how it does or does not impact a student’s grade. Policies like, “you’ll lose a letter grade if you miss X number of classes,” drive me nuts.

Yesterday, I decided it was time to sort out what the plan should be for presentations, WeBWorK Achievements, and attendance. I had read a short article about gamification in education (I can’t remember which article) recently and I thought, “hey, why don’t I just gamify this stuff that I’m not sure what to do with.” In general, I’m not a fan of offering points for things that students should naturally do (and I’m also sure I have tons of counterexamples to what I just said), but I’m going for it anyway. Maybe this is a horrible idea. Here is what I currently have on their syllabus.


As per university policy, attendance is mandatory in all 100-level courses, and in particular, I am required to record attendance each class session. Daily attendance is vital to success in this course! You are responsible for all material covered in class, regardless of whether it is in the textbook. Repeated absences may impact your grade (see the section on Achievements). You can find more information about NAU’s attendance policy on the Academic Policies page.

Presentations and Participation

Throughout the semester, class time will be devoted to students presenting problems to the rest of the class. In addition, we will occasionally make use of in-class activities whose purpose is to either reinforce/synthesize previously introduced concepts or to introduce new concepts via student-driven inquiry. If necessary, these activities will be explicitly graded.

I expect each student to participate and engage in class discussion. Moreover, I will occasionally ask for volunteers (or call on students) to present problems at the board. No one should have anxiety about being able to present a perfect solution to a problem. In fact, we can gain so much more from the discussion surrounding a slightly flawed solution. However, you should not volunteer to present a problem that you have not spent time thinking about. Your overall participation includes your willingness to present, engagement in and out of class, and consistent attendance record. Your grade for this category will be worth 8% of your overall grade and will be based on Achievements (see below).


This semester I’ve decided to “gamify” good student behavior. Here is the gist. I’ve generated a list of items that I deem good student behavior. Every time you achieve one of the items on the list, you earn some points. The more points you earn, the higher your Presentation and Participation grade (worth 8% of your overall grade in the course). So, how do you earn achievement points? Here’s a list.

Points Description
5 Stop by my office sometime during the first two weeks of classes. This is a one time offer and stopping by to just say hello is fine.
2 Stop by my office hours to get help. This goes into effect after the first visit and you can earn points for this up to 4 times.
1 Attend class, arrive on time, and stay the whole class meeting.
1/2 Attend class but arrive late.
1/2 Attend class but leave early.
2 Attend a review session offered by our Peer TA. You can earn points for this multiple times.
4 Stop by the Math Achievement Program to get help. This is a one time offer and you must get a “prescription” form from me in advance for a tutor to sign.
2 Find a typo anywhere on the course webpage, homework, exam, etc. These points are first come, first earned, but there is no limit to the number of times you can earn points for this.
5 Volunteer to present a problem to the class on presentation days.
3 Agree to present a problem to the class on presentation days after I’ve called on you.
2 Earn a non-secret Achievement in WeBWork. You can see list of possible non-secret Achievements by clicking on the appropriate link in the sidebar after logging in to WeBWorK.
3 Earn a secret Achievement in WeBWork. These shall remain a mystery.
2 Post a useful resource such as a video or link to a math-related website on our course forum.
2 Post a relevant question on our course forum.
2 Post a useful response to a question on the course forum that does not just give an answer away.
5 Earn at least an 8/10 on your highest score for a Gateway Quiz.

Important: Any time I feel you are taking advantage of the spirit of this, I reserve the right to take away an achievement point.

To calculate your grade for the Presentation and Participation category, I will divide your Achievement points by the maximum number of Achievement points earned by a student and then convert to a percent.

Feedback is extremely welcome. I’ll let y’all know how it goes.

Edit: One thing that I forgot to add is that I have a Peer TA for 10 hours per week. She attends class and has access to the course forum, etc. So, I’ll let her do most of the point tracking. Otherwise, I’d have trouble with the bookkeeping. Also, I decided to use the highest number of Achievement points earned by a student to calculate a percentage for each student. In the comments below, Strider suggested that I use the average of the top 3 instead. I like this idea, but I think I’ll use the top 5.

On Thursday, August 22, I was one of four speakers that gave a 20 minute talk during the Department of Mathematics and Statistics Teaching Showcase at Northern Arizona University. My talk was titled “An Introduction to Inquiry-Based Learning” and was intended to be a “high altitude” view of IBL and to inspire dialogue. I was impressed with the turn out. I think there were roughly 40 people in attendance, from graduate students to tenured faculty and even some administrators. Here are the slides for my talk.

If you take a look at the slides, you’ll see that I mention some recent research about the effectiveness of IBL by Sandra Laursen, et. al. During my talk, I provided a two-page summary of this research, which you can grab here (PDF).

After about 15 minutes, I transitioned into an exercise whose purpose was to get the audience thinking about appropriate ways to engage in dialogue with students in an IBL class. I provided the participants with the handout located here that contains a dialogue between three students that are working together on exploring the notions of convergence and divergence of series. After the dialogue, five possible responses for the instructor are provided. I invited the participants to discuss the advantages and disadvantages of each possible response. It is clear that some responses are better than others, but all of the responses listed intentionally have some weaknesses. We were able to spend a couple of minutes having audience members share their thoughts. It would have been better to spend more time on this exercise. I wish I could take credit for the exercise, but I borrowed it from the folks over at Discovering the Art of Mathematics.

If you want to know more about IBL, check out my What the Heck is IBL? blog post over on Math Ed Matters.

A couple of days ago, Peter Krautzberger sent me an email asking if I was interested in becoming an editor for According to’s about page:

From research to recreational, from teaching to technology, from visual to virtual, hundreds of blogs and sites regularly write about mathematics in all its facets. For the longest time, there was no good way for readers to find the authors they enjoy and for authors to be found. We want to change that. We have collected over 700 blogs and other news sources in one place, and invite you to submit even more! Our goal is to be the best place to discover mathematical writing on the web. is run by Samuel Coskey, Frederik von Heymann, and Peter. Felix Breuer also had a hand in the site’s creation. The current editors are Peter Honner, Fawn Nguyen, and Shecky Riemann.

Lately, I’ve been feeling stretched a bit thin, so I told Peter that I needed to think about it before deciding. I’ve been trying to be careful about the new projects I take on so that I don’t get in over my head. But…then I remembered the talk that Joe Gallian gave at the conclusion of my first Project NExT workshop in 2008. The theme of Joe’s talk (which he gives every year for Project NExT) is “just say yes.” His thesis is that by saying “yes” we open doors to new opportunities and by saying “no” we close ourselves off to what might have been. Okay, I’m sure Joe would admit that we shouldn’t say “yes” to everything, but I believe he would say that most of us say “no” too often.

I took Joe’s talk pretty seriously my first few years post PhD and I think it has worked out pretty darn well for me. There have been numerous times I thought that I should say “no” but followed Joe’s advice instead. Most of the time it has worked out for the best. A good example is when Ivars Peterson asked Angie Hodge and I to start blogging for the MAA. Actually, let me back up a notch. First, Nathan Carter suggested that I apply for the editor position at Math Horizons. I implemented Joe’s philosophy and talked Angie into applying with me as co-editors. Alas, we were not chosen and instead the committee selected the most awesome Dave Richeson. However, as a result of our application, Ivars approached Angie and I about starting up Math Ed Matters. Around this time, I was beginning a new position at Northern Arizona University and I was concerned that my tenure committee wouldn’t value this sort of work. I dragged my feet for a couple months, but eventually Joe’s voice in my head won out. Angie and I have only been blogging for a few months, but we certainly made the right decision. Lots of new opportunities have presented themselves as a result of the blog. I could go on and on about similar choices.

Okay, by now you’ve already guessed that I agreed to Peter’s offer. So, what does being an editor entail? I already keep up with quite a few math-related blogs, but now I just need to “star” the ones on that I find the most interesting/enjoyable/useful/compelling and leave a brief comment about them. Doesn’t sound too bad. Of course, to be fair I should start reading a few more of the blogs that pass through.

Yesterday was my first day on the job and I already selected two recent blog posts for Editors’ Picks:

  1. Name 5 top journals you read… by Peter Krautzberger
  2. A Problem with Assessment by TJ Hitchman

I’m looking forward to reading more excellent blog posts and seeing if Joe is right again.


When I was preparing my talk for the Legacy of R.L. Moore Conference a couple weeks ago, I reread the student evaluations for my introduction to proof course from Spring 2013. I was really pleased with all the comments, but two of them stood out because they capture the essence of what I want an inquiry-based learning (IBL) experience to be.

Here’s the first comment.

[…] he has found the perfect way to teach this course. […] The way Professor Ernst had us struggle through homework and then come together as a group and discuss the topics was very beneficial. I personally struggled through most of the material and when I finally got to the right concept I felt like I fully understood it because I personally came to that conclusion. Also, when I didn’t fully understand a topic, coming together and discussing it connected all the gaps I was missing. […] As a future educator, I would love to mimic his style of teaching so I can share with my students the same satisfaction that I got out of this style of teaching.

I stripped out a couple complimentary sentences that addressed me rather than the course. Of course, I’m thrilled about this student’s desire to incorporate IBL in their future teaching, but what I really appreciate about this comment is how the student reflects on both his/her independence and collaboration.

Here is the second, very short comment.

Try, fail, understand, win.

Four words of awesomeness. I couldn’t hope for more. This second comment inspired a recent post that Angie Hodge and I recently wrote for Math Ed Matters.

On Friday, June 14 I gave a 15 minute talk in one of the parallel session at the Legacy of R.L. Moore Conference in Austin, TX. The Legacy Conference is the inquiry-based learning (IBL) conference. In fact, it’s the only conference that is completely devoted to the discussion and dissemination of IBL. It’s also my favorite conference of the year. It’s amazing to be around so many people who are passionate about student-centered learning.
This was my fourth time attending the conference and I plan on attending for years to come.

Here is the abstract for the talk that I gave.

In this talk, the speaker will relay his approach to inquiry-based learning (IBL) in an introduction to proof course. In particular, we will discuss various nuts and bolts aspects of the course including general structure, content, theorem sequence, marketing to students, grading/assessment, and student presentations. Despite the theme being centered around an introduction to proof course, this talk will be relevant to any proof-based course.

The target audience was new IBL users. I often get questions about the nuts and bolts of running an IBL class and my talk was intended to address some of the concerns that new users have. I could talk for days and days about this, but being limited to 15 minutes meant that I could only provide the “movie trailer” version.

Below are the slides from my talk.

One of my goals was to get people thinking about the structure they need to put in place for their own classes. When I wrote my slides, I had a feeling that I couldn’t get through everything. I ended up skipping the slide on marketing, but in hindsight, I wish I would have skipped something else instead. Two necessary components of a successful IBL class are student buy-in and having a safe environment where students are willing to take risks. Both of these require good marketing and I never had a chance to make this point. Maybe next year, I will just give a talk about marketing IBL to students.

In the broad light of day mathematicians check their equations and their proofs, leaving no stone unturned in their search for rigour. But, at night, under the full moon, they dream, they float among the stars and wonder at the miracle of the heavens. They are inspired. Without dreams there is no art, no mathematics, no life.

Quote by Michael Atiyah

Math Ed Matters is Live!

April 12, 2013 — 2 Comments


Angie Hodge and I are excited to announce that Math Ed Matters went live earlier today. Math Ed Matters is a (roughly) monthly column sponsored by the Mathematical Association of America and authored by me and Angie. The column will explore topics and current events related to undergraduate mathematics education. Posts will aim to inspire, provoke deep thought, and provide ideas for the mathematics—and mathematics education—classroom. Our interest in and engagement with inquiry-based learning (IBL) will color the column’s content.

Our first post is isn’t terribly exciting; it’s just an introduction to who we are. Here’s a sample of what we hope to discuss in future posts:

  • How did Angie and I meet and how did we end up collaborating on this blog?
  • History and impact of Project NExT
  • Inquiry-Based Learning: What, Why, and How?
  • How and why did Angie and Dana start implementing an IBL approach?
  • What’s the Buzz? (Calculus Bee)
  • A recap of the 16th Annual Legacy of R.L. Moore Conference (June 13-15, 2013 in Austin, TX)
  • A recap of MathFest 2013 (July 31-August 3, 2013 in Hartford, CT)
  • Pivotal Moments: How did Dana and Angie get to where they are now?
  • Utilizing open-source technologies and text-books

We’d love for you to follow along and join in the conversation. What other topics would you like for us to discuss?

Thanks to the MAA for giving us the opportunity to share our musings with you!