David's blog

Err and err and err but less and less and less

David's blog

Err and err and err but less and less and less

Weird certificate verification error

I spent most of the day today debugging a very mysterious error we encountered when trying to programmatically call a web service over SSL from Java. Here is the source code with which we managed to reliable reproduce the error: import javax.net.SocketFactory; import javax.net.ssl.SSLSocketFactory; import java.io.*; import java.net.Socket; public class SimpleSSLTest { public static void […]

MATLAB’s inane idea of time

MATLAB seems to have a very peculiar notion on how to represent dates and times. Yesterday I spent a wonderful couple of hours debugging some code that’s supposed to compute the sun’s position, most of which could have been avoided if the MATLAB designers had followed a simple convention used by, I believe, most computing […]

Installing ESP-r on Ubuntu 9.10

ESP-r, is an integrated modelling tool for the simulation of the thermal, visual and acoustic performance of buildings and the assessment of the energy use and gaseous emissions associated with the environmental control systems and constructional materials, in the words of its official website. In other words, it’s a computer program for modeling a building’s […]

Alternatives to Java for home automation devices

I think there’s no escaping this simple fact: the Java Virtual Machine (JVM) is definitely here to stay, and all the evidence shows that it has tremendous potential for being used in home automation devices. I still remember from a previous life when we hunted for a JVM implementation that would run with a minimal […]

Why I’m disabling MathML for now

In a previous post I described how I tweaked my WordPress installation to support the display of MathML markup, for displaying mathematical equations. One of the steps involved changing the content-type from application/html to application/xhtml+xml. That step was necessary, or else Firefox would simply not render the MathML markup properly. Unfortunately, application/xhtml+xml is simply not […]

Equivalent conductance due to air infiltrations

Here is how you compute the thermal coupling between a room’s indoor temperature and the outdoor temperature due to infiltrations. The equation governing the exchange of heat is as follows: Cair × dT/dt = g × Δ T where Cair is the indoor air thermal mass [J/K], T is the indoor air temperature [K], g […]

Event rate of arrival analysis with R

Here is a very common problem: suppose you’re give a series of event timestamps. The events can be anything—website logins, persons entering a building, anything that recurs regularly in time but whose rate of arrival is not known in advance. Here is, for example, such a file which I had to analyze: 05.02.2010 09:00:18 05.02.2010 […]

Book review: Agile Project Management with Scrum

I began reading Ken Schwaber’s ‘Agile Project Management with Scrum’ for two reasons: 1) it’s a book about Scrum, and 2) it’s from Ken Schwaber, one of the fathers of Scrum. Having now read it, I think these are the only reasons I don’t entirely regret reading it. The book is a series of case […]

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