Older blog entries for vicious (starting at number 289)

New chapter for the Diffy Qs book

I’ve written up a new short (14 pages) chapter for the Differential Equations textbook. I’ve put a draft on the web for my students as I’ll start covering it tomorrow (it’s only going to be 2 lectures, though the chapter should be usable for up to 3 lectures).

I suppose after Monday (after I finish lecturing on it), I’ll feel good enough about it to post a new version of the whole book with the chapter 7 in there.

I’ve caught quite a few typos and errors in the book this quarter, though I would say not any more than one can find in any first edition textbook. It seems that commercial publishers are very good at catching English grammar errors, but are terrible at catching mathematical mistakes. My book has probably more bad English than your average textbook. But I’m now feeling pretty good now about the mathematical content being correct.

A funky news is that apparently someone at Dartmouth College is planning to use the book for a course in their Winter term. I only heard from the bookstore that they asked if they can make copies of the book for the students, not actually from the instructor. I wonder how many courses have already used the book. I only know of a few …

Syndicated 2010-11-11 19:14:25 from The Spectre of Math

Voters speaking loud and clear

So after every election here, whichever party won starts saying nonsense like “voters spoke loud and clear.” That is simply nonsense. In every one of these elections that were claimed as overwhelming wins for one party the popular vote never goes beyond 45-55 or vice versa. The house vote was 52-44 this time around, last time it was 42-52. Let’s just assume 45-55. That’s like if you have some sort of club with 20 people, one person changed their mind. Hardly a “voters spoke loud and clear.”

Furthermore, in these midterms there were fewer people voting for the winning party than there were voting for the losing party in the last elections. So it’s entirely possible (though very unlikely) that not a single new person voted for republicans. That’s like in your club of 20 people where your side of an argument had 11-9 majority, suddenly only 15 people show up and you have
a 7-8 minority (actually that would be far far worse in terms of percentage of vote than what happened in the midterms). The members of the club would not have spoken loud and clear. Actually perhaps nobody actually changed their minds, it was just that there was a furniture sale somewhere that they had to go to.

From my experience with clubs related to any sort of activity, this is precisely what always happens, and why morons take over at some point. Actually come to think of it, that’s exactly what always happens in any sort of politics too.

The democrats are just as much to blame on this as the republicans. Whichever side wins always claims absolute mandate of the masses, even though nothing so drastic happened. This even happens when one side wins by 1 or 2 percent, which is really something that could have gone either way if the weather was bad. So if you win within such a small margin, you might as well flip a coin, you won on a technicality. So many democrats were angry about Gore and Bush. But that was all within margin of error. Maybe if the elections were held a week later it would have gone the other way. It was 50-50, there was no majority for either side. The same thing happened in ’04, except the roundoff error seemed to have gone in favor of Bush.

There should be a rule against such rhetoric unless your side wins 70-80 percent of the vote and the voter turnout is so large
that over 50 percent of eligible voters actually cast their ballot for you.

Syndicated 2010-11-11 18:01:08 from The Spectre of Math

Damn Murphy!

Murphy’s law strikes again. The moment you publish something (be it a textbook or a software), you find a bug. Yesterday I put on the web new versions of both my diffyqs notes and my real analysis notes. Already yesterday I found that when I posted the real anal notes on lulu, I forgot to update the book cover to state that I’m now at UCSD. OK, that’s a minor thing, who cares.

Today I was preparing for my diffy qs class and found an error in the notes. Actually I think I spotted this error in the spring when I taught at UIUC, but somehow forgot to fix it. So I find the first significant typo in the notes the day after posting new versions of the notes. And putting up new versions of the diffy qs notes is not as trivial as it may seem. It takes about 2 hours just to build the HTML version. This is because I have tex4ht do all math as images. Doing some of the math using CSS is faster, but then you get different font for some equations (as some are done using images and some using CSS).

If jsmath actually worked right, I would use that. But since I generally have a hard time making jsmath display things correctly on my own system, I assume that it doesn’t work right for a lot of people. Also jsmath seems to break for me for the pages as large as the notes. Mathml would be the perfect solution if it would work properly and consistently on all browsers. Right now for mathml and tex4ht you have to first decide on a browser to support, which beats the whole idea.

Browser developers are generally interested in floating 3d fish rather than actually useful stuff like supporting mathml properly. One of the reasons I am sticking to firefox is because the fact that they do support mathml reasonably, and have for a while, is an indication of sanity on the part of the developers.

Syndicated 2010-10-04 19:45:34 from The Spectre of Math

number of unique ips

So I assigned homework in my differential equations class from my diffyqs notes and
the number of downloads from new ips jumped from the regular 90-100 to first week 131 and then this week (when the homework was due, 363. So subtracting 100 from each week for non ucsd downloads (I could check the logs, but I don’t have so much disposable time) I get that approximately 294 (let’s round that to 300) downloads from unique IPs are from my class. There are 180 students in my class, so each student on avarage downloads the notes from 1.67 different IPs (different devices).

On the other hand, the real analysis notes are holding at approximately 200 new ips a week. I know for sure that these are used in at least one class this fall. Given that the jump from summer to fall was from approx 110 to now 200 a week, that would over the last few weeks perhaps lead to up to 350 downloads from new ips that come from students who use that book, meaning about 200 students extrapolating from the diffy qs classes. Since the usual class size for this is 20-40 students, that mean 5 to 10 classes might be using this book. On the other hand, it may simply be students that find the book as a second reference. It would be interesting to know the real number.

Syndicated 2010-10-03 18:07:01 from The Spectre of Math

new genius

I figured I ought to make a genius release before it is a year since the last one, so 1.0.10 is out then. A bunch of minor updates have accumulated but nothing major. Biggest change was that I added possibility to rename variables in the plotting interface so that I can set variable names to those that I am talking about in class. That reminds me to check on the availability of computer projectors in the classrooms I’m teaching in at UCSD.

Syndicated 2010-09-08 08:42:47 from The Spectre of Math


An interesting trend: Downloads from new IPs of my differential equations notes have not spiked in the last week or two, while the real analysis notes have. See (weekly downloads from new IPs, blue is real analysis, red is diffy qs):

(I wonder if the chart will change when I update the the spreadsheet in google docs in the future … we’ll see. The spike I am talking about is of course for the week ending 9/5/10)

My theory is that the differential equations notes are not used as official book in any course (that’s on a semester system), while the real analysis notes are used as official book somewhere. The diffy qs notes tend to spike a little near time of midterms which seems to imply that people use it for extra reference. Also two (yes that’s two) people have bought the bound copy of the real analysis book in the past month, which triples the volume of sold copies. When I taught with my diffy qs notes, I got 5 sales. If it’s the official book, it seems more likely that someone will still buy a hard copy even if they can download and print the book for free (well given cost of printing and simplest binding, it’s not that much cheaper actually).

Syndicated 2010-09-06 17:14:35 from The Spectre of Math

Adobe acrobat is possibly the worlds slowest software

See title. It took about 5 minutes to open a pdf that evince opens in a second or two and that xpdf opens essentially instantly. I was ready to xkill acrobat. Unfortunately for whatever reason evince did not allow me to click checkboxes in a form so I needed acrobat.

Talking about slow applications, the cannon mp560 printer scanner is taking about the equivalent time to scan a single page now. But here I assume it may have to do with the fact that I am using it over wifi.

Syndicated 2010-09-01 19:07:04 from The Spectre of Math

directed acyclic graphs suck for a vcs

DVCS systems like git work on a directed acyclic graph (DAG) model where branching happens automatically with just about any commit. Traditional vcs (e.g. CVS) works generally as a tree where branching must be explicitly done.

Now the argument for DVCS is that you can commit without merging differences done by someone else. The axiom seems to be

Axiom of DVCS: Merging should be done as late as possible.

What’s wrong with that? Well nothing if you are happy for the computer to just blindly merge two very divergent code bases without worrying about interactions of those changes (you kept hacking on feature A which required that function foo works in a certain way, while person working on feature B changed how foo works because he didn’t see anybody use it yet because your use of it was in a branch that the second person of course didn’t look at because he was busy working on feature B). No that never ever happens because all developers always talk to each other about every little change and because every internal function/method/object is completely documented. Yeah.

With traditional VCS, merging is required when checking in. The axiom changes to:

Axiom of traditional VCS: merging should happen as early as possible when divergence is as small as possible.

When everyone continually has to keep up with all the other changes that other people are working on, possibility of screwing up is smaller. Merging other people’s changes into your tree can be far simpler if it was just someone’s morning worth of work with say 100 lines of code. You can actually look at that quickly to review what happened. Not to mention you will have to look at it if there are direct conflicts with your work. Furthermore, if the other person changed how function foo works, you will notice sooner rather than later so you can resolve the conflict before both of you go too far assuming function foo works in a certain way.

I know exactly why DVCS is more popular nowadays. Firstly it is new and new things are always better even if they are worse. Second, it is more complicated, and complicated things must always be better. But most importantly of all: DVCS has a lot more buzzwords. It is distributed, it uses directed acyclic graphs (finally you have a use for some of your CS classes). Lots of things that work are replaced continuously by complicated things that don’t.

Example: I would say the level of the desktop software (Windows, Linux, and Mac) has not improved substantially. It has changed yes. It does lots of graphical voodoo. It allows you to do things that nobody ever wants to do. But if you took a basic desktop from the year 2000 and you simply fixed it to work right, you’d have a much faster, much more productive environment. But fixing things is not as much fun as rewriting a desktop on OpenGL, making windows wiggle, and making a different funky widget set for each application.

Syndicated 2010-08-31 19:28:10 from The Spectre of Math

San Diego wants to kill you (if you walk)

San Diego, especially it seems north San Diego, is one of the worst places to be a pedestrian. Many places without sidewalks, crosswalks, very wide divided streets, etc…

But the worst part of all is the following. Someone had the bright idea that a crosswalk should exist on only 3 sides of an intersection instead of 4. Now, it is possible to go from any point to any point, but it can take very long. Sometimes you need to cross a busy street 3 times just to cross at one point (if you want to do it legally). I am not sure what is the advantage to the cars, but I assume the advantage is very minor. This means that you force a pedestrian to cross more crosswalks OR to jaywalk. That doesn’t seem like a way to improve safety, nor to reduce driving (you know to reduce carbon footprint, etc…) San Diego is apparently among the most dangerous places for a pedestrian. I think I know why. I think the city council hates pedestrians.

Not that the streets here are optimized for cars either. There are so many divided streets, no u-turn signs, etc… If you miss a turn in San Diego you might be likely to drive quite a lot longer (especially in rush hour). Or in some parts, just getting to a store that just happens to be on the other side of a divided street can be an operation involving several traffic lights and breaking a few rules.

Syndicated 2010-08-31 16:00:46 from The Spectre of Math

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