Capitalism and Arithmetic and Casting Out Nines
Recently, I borrowed a copy of Frank J. Swetz’s book, Capitalism & Arithmetic: The New Math of the 15th Century (sadly, there is no PDF on the Internet, to the best of my knowledge). It was really...
View ArticleFun with n-grams, part 2: tightly packed tries
Follow-up to part 1. Last time, I talked a little bit about an implementation of a trie to store frequency information about n-grams. The problem is that the naïve implementation of a trie is much more...
View ArticleFun with Google n-grams data (part 1)
As part of the Google Books digitization project, Google created a dataset of n-gram frequencies. The Google Books Ngram Viewer is their presentation of this data, but Google also provides the raw data...
View ArticleConverting KML files to shapefiles with extra data
GIS data comes in tons of different formats (and some formats that are the same, but with different CRSs, etc.), and often you have to convert one to the other. The ogr2ogr tool that comes with GDAL is...
View ArticleBetter Living Through Clang-istry
Recently I came across this article, explaining how to use clang to dump the memory layout of a C++ object. Running clang -cc1 -fdump-record-layouts ppfile.cpp on a preprocessed C++ file, produced...
View ArticleNotes on my Arch Linux install
I reinstalled Arch on my desktop, and these are my notes-to-self on what I did differently from the install guide, so I don’t forget. bcache and btrfs Follow the instructions on the Arch wiki: install...
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Haskell, Lasers, and Curved-Fold Origami
About a year ago I wrote about some cool curved-fold origami patterns that make circular saddle shapes when they’re folded. Recently, I was back in Toronto, and while I was meeting my friend Chris, we...
View ArticleKStars GSoC: OpenCL and a first performance report
These past two weeks or so, I’ve been working on a nice interface for KStars to use OpenCL with. The problem is that OpenCL support is still pretty flaky in terms of support – at the moment, there are...
View ArticleKStars GSoC: Aberration with a Stereographic Projection
Part of my summer of code project involves rewriting the KStars code so that it uses 3D cartesian coordinates to represent points on a sphere, instead of using spherical coordinates and having to do...
View ArticleKStars GSoC: Progress Update
Here’s a brief update on the progress with KStars. The main accomplishment so far is writing new implementations of the coordinate conversions that KStars uses to calculate the positions of sky...
View ArticleIntel VTune on Linux 3.9 workaround for hlist_for_each_entry
Recently I was installing Intel’s VTune on a machine with Linux 3.9. When I tried to install the sepdk driver for profiling, it failed to compile task_map.c with several errors similar to error: macro...
View ArticleQuaternions and Rotations
In my last post, I discussed the coordinate systems used in KStars, which all used two-dimensional spherical coordinates. However, the coordinate systems are perhaps better thought of not in terms of...
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Coordinate Systems in KStars
This post describes a few of the coordinate systems that KStars uses to keep track of the positions of various astronomical objects, and how they relate to one another. All of the points used in KStars...
View ArticleKStars Summer of Code 2013
Hello Planet KDE — my name is Henry de Valence, and I’ll be doing a GSOC project this summer for KStars. The main goal of the project is to rewrite the astronomy engine in KStars so that it runs much...
View ArticleLord Thomas Macaulay on Copyright (1841)
I recently came across the transcripts of two speeches delivered in the House of Commons by Thomas Babington Macaulay in 1841/2 (For the curious: he was raised to the peerage only later; at the time,...
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JPEG compression and retina displays
There’s an article here which describes a method for providing higher-resolution images to users with high-resolution displays. It seems like a bit of a free lunch to be able to suddenly get much...
View ArticleQOTD: Newton on Cassegrain
I recently found a wonderful article while browsing old public domain articles – Philosophical Transactions of the Royal Society from the late 17th century. Here’s Laurent Cassegrain, presenting his...
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A portable photocopier with OpenCV
I wrote some software recently that uses OpenCV to act as a sort of “portable photocopier”. The idea is to be able to take photos on a portable camera (e.g., like the one on a mobile phone), and then...
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Beware poor quality in Springer GTM books
Compare and contrast the following pictures of text, from two Springer GTM books. This is from Silverman’s The Arithmetic of Elliptic Curves: And this is from Hartshorne’s Algebraic Geometry: Both are...
View ArticleElliptic Curves, Lattices, and the Upper Half-Plane
This post is a rough sketch at writing down my understanding of the correspondence found on page 36 of Silverman’s Advanced Topics in the Arithmetic of Elliptic Curves (ATAEC), following material there...
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