Other articles

  1. Collaborative tools

    I do quite a bit of collaboration. In fact, since after my PhD research, I have written exactly one preprint that does NOT spring from a collaboration. And there is quite a bit of technological support that flows into a good collaboration of mine. Here are some of the tools ...

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  2. Some thoughts on fire photography

    First off: I would like to apologize to the readers I still have that I never get around to updating here. I am aware that I'm writing less than once I was planning to.


    I have grown very interested in photography, as those of you who have seen ...

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  3. Geometric realization of simplicial sets

    This post is an expansion of all the details I did not have a good feeling for when I started with for page 7 of Goerss-Jardine, where the geometric realization of simplicial sets is introduced.

    The construction works by constructing a few helpful categories, and using their properties along the ...

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  4. Teaching and seminars up ahead

    I'll be talking quite a bit in the next couple of weeks; here's a “heads up” for those who might want to come and listen.

    25 August, 1pm, Linköpings Universitet. The topology of Politics.

    1 September, 10am, KTH. Combinatorial species, Haskell datatypes and Gröbner bases for operads.

    1 ...

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  5. Itinerary for the Summer

    A few things that may interest people.

    1. I'm going on the job market in the fall. I'm looking for lectureships, tenure tracks, possibly 2 year postdocs if they are really interesting.

    2. I'm very interested in adding visits, adding seminars, adding anything interesting to this itinerary ...
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  6. Another kind of sports reporting

    Inspired by John Allen Paulos, who just now tweeted

    Obvious, but NBC hasn't said: Canada, Norway, Germany way ahead of US in Olympic medals per capita. Many ways to rank: Cf. Arrow's theorem.

    I decided to redo the medals list. Here, the number of medals per capita among ...

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  7. [MATH198] Multiple lectures posted

    I have been remiss in updating here. Since the last time I posted, I have posted:
    Lecture 6, featuring some interesting limits and colimits, culminating in the introduction of adjoints.

    Lecture 7, featuring the introduction of monads based in adjoints, with the connection between the monoid of endofunctors and the ...

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  8. [MATH198] Lecture 5 is up

    And, as it turns out, my logic-fu is lacking. Next time around, it's likely I talk about the CCC = typed λ-calculus correspondence, but won't try to actually produce the correspondence explicitly.

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  9. Soliciting advice

    Dear blogosphere,

    come this fall, I shall be teaching. My first lecture course, ever.

    The subject shall be on introducing Category Theory from the bottom up, in a manner digestible for Computer Science Undergraduates who have seen Haskell and been left wanting more from that contact.

    And thus comes my ...

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  10. Guess the plots!

    What do these depict?


    Here are two others. Different data source, different point in time, but what are they?


    They are all linked in pairs - one coloured and one black linked together. They are not sports related. And they are taken from real world data. The colours are relevant and ...

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  11. Mapping zipcodes in R

    I started fiddling around with R again, and ended up playing with a zipcode database.

    So, first I downloaded the zipcode database at Mapping Hacks, and unpacked the zipfile in my working directory.

    Then, I loaded the data into R

    > zips <- read.table("zipcode.csv",sep=",",quote="\"",header=TRUE)
    > names ...
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  12. 1-manifolds and curves

    I have been painfully remiss in keeping this blog up and running lately. I wholeheartedly blame the pretty intense travel schedule I've been on for the last month and a half.

    To get back into the game, I start things off with a letter from a reader. Rodolfo Medina ...

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  13. Picking fights over religion

    I suspect this will be a flame war magnet. On the other hand I feel compelled to write it.

    First a bit of backstory. My wife enjoys, often and with engagement, discussing theology with her new friends. One of them, a pentecostal christian, gave her the book I don't ...

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  14. Site tweaks and travel plans

    I've tweaked the layout of my blog a little bit. Among the more notable additions to it is the little box with a list of the major travel plans in my future.

    This box is connected to a Google Calendar, public, and maintained from my normal calendar program, in ...

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  15. RIP Henri Cartan

    As John Armstrong said, I didn't know he was still alive!

    On the algebraic topology mailing list, the announcement came today that Henri Cartan, once co-founder of Nicholas Bourbaki, died August 13, 2008:

    La Soci
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  16. The end of the line

    And a new beginning.

    We seem to be a whole crowd finishing our PhDs all at the same time: pozorvlak, Gooseania and I. While my blog started as inspired by Gooseania, I won't close it just because I'm done. I'll continue blogging my Postdoc years, and hopefully ...

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  17. A vision for collaborative mathematics platforms

    Based on the extensive discussion at the Secret Blogging Seminar on tools for long-distance collaborations, Scott Morrison writes an introduction to source control with subversion for research collaborators.

    In this post, Scott also offers, quite magnanimously, to setup and host subversion repositories for any mathematician who happens to want to ...

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  18. Tour dates

    Edited to add Galway

    I'll be doing a "US tour" in March / April. For the people who might be interested - here are my whereabouts, and my speaking engagements.

    I'm booked at several different seminars to do the following:

    Title: On the computation of A-infinity algebras and Ext-algebras
    Abstract ...
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  19. Thesis written

    In a mean push, these last two weeks my advisor has read three different drafts of my thesis. And I've worked on getting the corrections in quickly. The last push started yesterday, when I got a bunch of corrections in the morning, had the last draft ready at 4pm ...

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  20. JMM Blogger Meetup!

    There's a bunch of us math bloggers on site in San Diego. Hence, here, the call for a blogger meetup. We'll convene by the entrance to Hall B (the one with the registration and the exhibitions) at 6pm on Tuesday 8th.

    I'll be there, and so will ...

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  21. The year 2007 in review

    From each month, the first sentence of the first post.

    January: I decided on a whim to look in at the Dilbertblog, where the top post at the moment has Scott Adams calling all atheists that discuss on the net irrational, using a rather neat strawman carbon copy of most ...

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  22. Papers status

    I just received my first ever referee's report. Yikes!

    Suffice to say, the report did not, as some I've seen blogged about, tear me a new one. Far from it - it was civil, kind, and pointed out several areas where my article text overlapped known arguments from other ...

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  23. Planning the future

    The last meeting with my 10th grade topology kids this year just finished. We introduced singular homology, calculated the singular homology of a point and discussed homeomorphism invariance.

    Next term, we'll want to show homotopy invariance and that the singular and simplicial homology coincide when applicable. After that, we ...

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  24. Pluralization in Rails

    So, there is this one big and neat framework called Rails, building on top of this one neat new programming language called Ruby.

    And one of the things that makes Rails so Damn Neat is that if you only set things up the right way around, it guesses almost everything ...

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  25. Reaching for the postdoc world doorknocker

    The last postdoc carnival for 2007 is coming to town, and given my current position in my career, I thought I'd try to slowly edge into that arena as well.

    A short background blurb for those who haven't read this blog before - and for those who haven't ...

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  26. Synaesthesia and cognition

    Published: Mon 03 December 2007
    By Michi

    In Blogs.

    So, there is this one condition called synaesthesia, where basically perception gets crosslinked. Most commonly, numbers, letters, and words get colours coupled to them. This way around, I have a few friends who I know have it.

    The more exotic varieties couple more or other senses to each other.

    The ...

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  27. Comments temporary disabled

    Due to a spectacular spam storm incited by akismet.com being unreachable from the webserver, I have decided to globally shut off commenting for the time being.

    This should be a temporary state, and I hope that the akismet issue solves itself soon.

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  28. Beef sous vide

    I tried out an idea from Khymos recently when inviting a bunch of friends over for a party. We took six slices, about 1100g, of beef entrec

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  29. Wreath products

    In a conversation on IRC, I started prodding at low-order wreath products. It turned out to be quite a lot of fun doing it, so I thought I'd try to expand it into a blog post.

    First off, we'll start with a definition:

    The wreath product [tex]H ...
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  30. Settling in in Sydney

    No mathematical content today. However, I do note that the mathematics department in Sydney is located in a building as drab and boring as the Stockholm University main building. Its main architectural feature is the pale, washed out blue panels on the upper parts of the hollow concrete slab.

    Just ...

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  31. Still away

    However, I am enjoying the Scottish countryside and just - today - turned [tex]3^3[/tex] years of age.

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  32. Coq and simple group theory

    Trying to make the time until my flight leaves tomorrow go by, I played around a bit with the proof assistant Coq. And after wrestling a LOT with the assistant, I ended up being able to prove some pretty basic group theory results.

    And this is how it goes:

    Section ...
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  33. Advertising policy

    Today I received an email kind of convincing me that my blog gets seen. It offered me $35 to put up an add for a phone service on one of my old blog posts.

    What differentiated this offer from all other spam I get was that it was actually written ...

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  34. AucTeX hackery

    One thing that has been bugging me for quite some time with AucTeX (which I love, in general) has been that I wasn't able to reset the bloody hot key for math mode input.

    The original setting maps to Shift-key left of backspace-space, since it's an accent key ...

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  35. In-between times

    These are the times that eat my productivity. The times that ensure that entire days go by and I afterwards feel nothing have happened at all. These times that are too short for productive work - where I know from the beginning that I cannot sit down and do something - too ...

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  36. Slumps and crunches

    This term of teaching ends next week.

    When I got back from T'bilisi, just over a month ago, I had research leads that I expect will end in three different publications.

    I was slated with writing one LARP report for a swedish gaming magazine, and a series of various ...

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  37. The why and the what of homological algebra

    I seem to have become the Goto-guy in this corner of the blogosphere for homological algebra.

    Our beloved Dr. Mathochist just gave me the task of taking care of any readers prematurely interested in it while telling us all just a tad too little for satisfaction about Khovanov homology.

    And ...

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  38. Sudden responsibilities

    I just met up with the workgroup in the Deutsche Mathematikervereinigung (German Association of Mathematicians) with interest spanning "Information and Communication" - which turns out to mean that they care about libraries, about communicative tools for mathematicians, and spend their time thinking about these things, and meeting at conferences.

    Met up ...

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  39. Representation theory - basics

    Many interesting groups have a very geometrical definition: transformations that fix certain symmetries is one of the historical origins of group theory.

    Thus, one of the most interesting classes of finite groups are the rotation and reflection symmetries of a regular polygon. These are called [tex]D_n[/tex], for a ...
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  40. Bright students and topology

    Today, I started an experiment together with the local specialised secondary school. I'll be taking care of two of their brightest students, meeting them roughly once a week, and taking them on a charge through algebraic topology. At the far end shimmers knot theory and other funky applications; and ...

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  41. On religion

    I decided on a whim to look in at the Dilbertblog, where the top post at the moment has Scott Adams calling all atheists that discuss on the net irrational, using a rather neat strawman carbon copy of most discussions of faith between believers (i.e. mostly Christians) and atheists ...

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  42. Why Blog?

    The Community College Dean has written about why he blogs, and asks any and all readers to tack on to his effort.

    My blog is not very anonymous. It is occasionally personal, occasionally political and throughout a venting location for thoughts, and a place where I formulate myself in higher ...

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  43. Weekly Report: Parties and lectures

    The term has started. In full force. No seating in the lunch cafeteria, lot's of people all over the place, lot's and lot's of new students, and lectures and examples classes kicking off all over the place.

    I'm leading an example class this year: linear algebra ...

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  44. Todo and accomplishments


    • I am done with the coursework for the past semester. Sent off the TeXed up solution sheets to the webmaster today.
    • My pattern observation seems to hold up surprisingly well - there seems to be a theorem to fetch out there somewhere.
    • I have done most of the dishes. Go ...
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  45. Admin: Wordpress 2.0

    This blog just migrated to WP 2.0. Should anything be odd, please notify me.

    The migration was to a large portion motivated by commenting problems I've been told about. I hope that my readers out there will be able to comment now; possibly even without logging in!

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  46. Weekly Report: Preparing to leave

    I left Jena going to Stockholm on Saturday. Thus, much of the week past has been spent in preparation for the trip - reading up on homotopical algebra; getting all the paperwork together and getting my things together for the trip.

    Along with "Make sure you learn homotopical algebra" and "Get ...

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  47. Weekly Report: Forgot all about it!

    Right. It's thursday. And I had some sort of hopes to do my weekly reports on saturdays. Only, last saturday found me back in Nuremburg, in the middle of a marathon party-after-party session with the RPG crowd there.

    Last week was very much characterized by getting various conditions for ...

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  48. Weekly report: Settling in

    My first week has passed. Today is saturday; and the move took place monday. So far, I've been running around doing bureaucracy and little else (I managed to leaf through the first 5 pages of Evens: Cohomology of Groups). Along the lines - I've received a summons to appear ...

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  49. Why I keep organizing congresses

    Once upon a time, I wasn't passionate about mathematics. Up to grade 6, I even disliked it quite a bit - it consisted of only mechanical plugging away of numbers, and training of multiplication tables that I had the feeling I already mastered.

    Then something changed. Subtly at first - in ...

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  50. Anti-spam measures

    After having a visit of some 5+ spams (I'm known by the spam bots! Is that good?) I just installed a captcha-like plugin. It requires some basic arithmetic skills from y'all; but on the other hand, I -am- a math blog after all.

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  51. Monads, algebraic topology in computation, and John Baez

    Todays webbrowsing led me to John Baez finds in mathematical physics for week 226, which led me to snoop around John Baez homepage, which in turn led me to stumble across the Geometry of Computation school and conference in Marseilles right now.

    This, in turn, leads to several different themes ...

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  52. Reading Merkulov: Differential geometry for an algebraist (1 in a series)

    I'll do this in posts and not pages on further thought...

    Sergei Merkulov at Stockholm University gives during the spring 2006 a course in differential geometry, geared towards the algebra graduate students at the department. The course was planned while I was still there, and so I follow it ...

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  53. Some math-y jokes

    You may have seen some of these before...



    [tex]\frac{\partial}{\partial x}\sin^2(x)=\sin(2x)[/tex] -- just move down the 2.

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  54. Merlots chokladtårta

    100g hasselnötter
    100g Marie chokladkex
    1 msk kakao
    3 tsk farinsocker
    (1 msk rom)
    30g smält smör
    40g smält mörk choklad
    200g mörk choklad
    30g smör
    1 1/4 dl ovispad vispgrädde
    3 äggulor
    2 ½ dl vispad vispgrädde

    Tillbehör: Färska frukter och bär

    Samtliga botteningredienser mixas i ...
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  55. The role of almonds in Swedish marital trends

    The role of almonds in Swedish marital trends

    Mikael Johansson, Susanne Vejdemo


    In this paper, we investigate the Swedish folkloristic belief that almonds in the Christmas rice porridge will lead to marriage. We offer a falsification of this hypothesis.
    Keywords: Christmas traditions, almonds, porridge, marriage


    One old folk ...
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  56. Calligraphy before christmas

    I sat down and started my calligraphy again recently. A few of the things I've done have not been saved for posteriority, but a few of them have been scanned and are available for display.

    All images are clickable for the full version.

    First, a sampling of the inks ...
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  57. EU Parliament clubbing Big Brother light

    Since roughly september, a resolution has been making its way through the EU bureaucracy to institute mandatory storage times for, among other things, internet traffic logs with ISPs. Throughout the discussions, the image has been coming through that the resolution would in endeffect require ISPs to log more or less ...

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  58. New directions!

    The byline is probably the most basic motivation for the blog. I want a place to write where I can expound upon themes I don't write in my LiveJournal - where I write articles rather than notes, where I publish creations I happened to make (I've started calligraphy - expect ...

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