Archive for the ‘Commentary’ Category

Google interviews

From an interesting blog post about the level of depth during a Google technical interview:

They also sent me an email with advice. It can be summed up as “You should know everything. If it’s to do with computers, you should know it. Here are 5 books and 4 fancy algorithms you should read. You must also be intimately familiar with all these basic-ish algorithms. This is your two week notice. Good luck. Oh and take a look at these videos too!”

I have a few friends who work at Google, and they are all top-notch engineers and thinkers, so it’s not a coincidence. Any good organization has a technical screening process that covers more than just the basics, and it looks like Google is no exception. In fact, the above note makes it seem like they go out of their way to ensure the candidate comes prepared to show their best, something that not all companies do. In this case, the important thing to note is that Google is more interested in smart software engineers than simply web developers.

Edit: For whatever reason, the linked blog is down. However, the cached version of the blog can be found here (cached by Google… so meta).

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Free Range VHDL

Free Range VHDL, by Brian Mealy and Fabrizio Tappero, is the latest in a long line of books written about VHDL. What makes this a unique offering is its simplicity as an introductory text, and the fact that it is absolutely free. The book is offered under the Creative Commons Attribution-ShareAlike Unported License, and can be downloaded in PDF and LaTeX format from the Free Range Factory website.

The book is far from a complete reference on VHDL, missing coverage of several important topics. These omissions are actually the basis for its strength. As anyone trying to learn a new language can attest, there is a fine line between introducing basic concepts and overloading the reader with unneccesary information. If you want to learn VHDL, this book may not be the final word, but can most certainly serve as the first.

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With the news today about a proposed overhaul of college financial aid that would create a dependence between aid programs and the affordability of an institution, there is a sense that the trend of migrating more collegiate-level education to the online classroom will continue at an accelerated pace.

In order for an educational institution to improve affordability and value for students, they drastically need to either cut costs, improve enrollment using the same resources, or both. Online education has the potential to reach whole new markets around the world, as shown by the recent example of Sebastian Thrun‘s class Introduction to Artificial Intelligence. The Stanford professor allowed anyone to enroll for the class for free and taught the exact same course material and handed out the same homework assignments as the paying students. The response was overwhelming, to the tune of more than 160,000 students world-wide. Some students created an online study group on the aggregation website Reddit. Here is NPR’s story about Thrun’s class on All Things Considered.

That this is more affordable to an institution is unquestionable. Once the lectures are recorded, universities need only provide the server capacity to handle student clients from all over the world. Online tests and homework assignments make the job of grading that much easier. Humans need not be involved once everything is in place.

The benefits of online education are numerous, but two points stand out above the rest: the lowering of educational costs, and the ease with which quality education will reach parts of the world (and the country) where this was not possible before. One of the greatest causes for concern with a young family is the kids’ college fund. Wages have to keep up not only with inflation, but with already-astronomical and still rising educational costs.

Thrun’s experiment in reaching students around the world made him realize the importance of reaching such a wide and socio-economically disadvantaged audience. He has now started an online university called Udacity, offering free online coursework to anyone around the world. Other initiatives have been in place for longer, such as the Khan Academy, MIT’s OpenCourseWare initiative and the OpenCourseWare Consortium.

Initiatives like these indicate that the established providers of quality education are about to see a rapid rise in competition for students and their tuition fees. As the competition heats up, there is a push for more conventional universities to shift to a more technology-driven curriculum in order to lower their cost-per-student. It may be easy to dismiss faculty concerns as threats to entrenched interests, but there are some genuine concerns.

Once the material has been recorded and uploaded, universities have little incentive to update the material as often, given the relatively higher cost to re-record lectures and keep the material fresh. There would be a disturbance in the environment that fosters bidirectional exchanges of ideas and the organic atmosphere between students and instructors that tends to improve lecture styles year-over-year. The material and focus of the lectures may not be as dynamic and responsive to student needs as the semester progresses. Finally, there would be a threat to the teaching profession as fewer professors are hired, reducing the amount of fundamental research done at the university.

Indeed at Stanford University itself, there is a renewed sense of urgency to provide a more diverse portfolio of online coursework such as their Center for Professional Development and the Stanford Engineering Everywhere programs. It remains to be seen whether the online classroom will ultimately prove to be a great boon to education, but it is clear that the upside in the short-term far outweighs the downside.

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An even faster Fourier transform

A group of MIT researchers have found a way to speed-up the fast Fourier transform for certain types of input data. The technique is described in an unpublished paper, which can be downloaded at this link.

From their abstract:

We consider the problem of computing the k-sparse approximation to the discrete Fourier transform of an n-dimensional signal. We show:
• An O(k log n)-time algorithm for the case where the input signal has at most k non-zero Fourier coefficients, and
• An O(k log n log(n/k))-time algorithm for general input signals.
Both algorithms achieve o(n log n) time, and thus improve over the Fast Fourier Transform, for any k = o(n). Further, they are the first known algorithms that satisfy this property. Also, if one assumes that the Fast Fourier Transform is optimal, the algorithm for the exactly k-sparse case is optimal for any k = nΩ(1).
We complement our algorithmic results by showing that any algorithm for computing the sparse Fourier transform of a general signal must use at least Ω(k log(n/k)/ log log n) signal samples, even if it is allowed to perform adaptive sampling.

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Logic and madness

What do Bertrand Russell (philosopher, logician and mathematician), Gottlob Frege (the great logician), Georg Cantor (inventor of set theory), David Hilbert (inventor of Hilbert spaces), Kurt Gödel (guru of incompleteness theory), Ludwig Wittgenstein (god of 20th century philosophy), the Greek city of Athens, the Oresteian trilogy and a dog named Manga all have in common?

They all star in the 2009 graphic novel Logicomix: An Epic Search for Truth, written by Apostolos Doxiadis and Christos Papadimitriou, drawn by Alecos Papadatos and colored by Annie Di Donna. It’s a rip-roaring tale of passion and madness, mixing fiction and reality, with frequent breaches of the fourth wall, and all presented through bright and colorful art and word balloons. For anyone interested in Logic, Mathematics or Philosophy, it presents Russell’s maddening journey during his quest for establishing the foundations of mathematics through logical certainty. It was during this journey that Russell, along with Alfred North Whitehead, wrote their seminal three-volume work, Principia Mathematica.

I first read about the book in the New York Times’ Sunday Books Review way back in the fall of 2009, but was only able to read it during a recent vacation. The story is engaging and entertaining, with just enough provocation for those who are more theoretically inclined to continue learning about these pioneer logicians beyond the pages of the book itself. The art is very reminiscent of Hergé’s ligne claire drawing style. Highly recommended.

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Blogger’s block?

No one ever gets talker’s block. No one wakes up in the morning, discovers he has nothing to say and sits quietly, for days or weeks, until the muse hits, until the moment is right, until all the craziness in his life has died down.

Why then, is writer’s block endemic?

From an interesting blog post, complete with bonus link to Ira Glass interview.

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Patently interesting

I’m a pretty big fan of Ira Glass and his radio program, This American Life, and I try to listen to every episode possible. My recent travels have hindered this, and I’m only now starting to catch up with some missed episodes from the summer. A recent episode titled When Patents Attack! really caught my ear.

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The dwell angle is a measure of the length of time that current flows through the primary circuit of an ignition system. The ignition system in question is within the context of an internal combustion engine, and operates by charging and discharging an ignition coil to provide periodic bursts of high voltage to the spark plugs. A distributor is used to regulate and route these periodic voltage bursts from the coil to each cylinder’s spark plug in a specific firing order. Within the distributor, the routing of voltage bursts occurs by means of an engine-driven rotor, which sequentially comes close to (without touching) the leads connected to each spark plug. In a mechanical distributor, the regulation of voltage bursts is achieved by means of a contact breaker switched by an engine-driven cam.

The contact breaker (also known as the “points”) is used to connect and disconnect the primary winding of the ignition coil. When the contact is broken, the sudden current loss induces a very high voltage at the output of the coil. The coil itself is actually a series of many windings. This creates a high voltage arc from the distributor rotor to the correct spark plug lead, which in turn causes a high voltage arc across the spark plug itself, within the combustion chamber. The ratio of the length of time the contact breaker is closed, to the distributor’s period of rotation, is known as the dwell angle. As the name implies, dwell angle is measured in degrees.

For example, in a six-cylinder engine, 360° of distributor rotation leaves sixty degrees during which the ignition coil can be charged and discharged for each cylinder. A typical 1960s-era Mercedes-Benz fuel-injected straight-six engine (for example, the M130) with a single-point distributor specifies a dwell angle range of 38° (± 3°). This implies that in a perfect system, the coil is charged for 38° and discharged for (60°-38°=) 22° for each of the six cylinders.

Dwell angle is measured by connecting a dwell meter to the coil’s primary circuit. The dwell angle is adjusted by changing the contact breaker gap (known as “gapping the points”). The contact breaker gap is meaningless in the face of the actual dwell angle measurement. If the dwell angle is too big, the coil remains charged for too long, and this can result in high coil temperatures which may lead to premature coil failure. If the dwell angle is too small, the coil is unable to develop sufficient field strength in order to provide a high enough voltage for the spark plugs (a “bad spark”).

To a computer engineer, the current flowing through the points looks like a clock signal, oscillating between zero (open circuit) and one (closed circuit). In the example of the aforementioned Mercedes, there are six clock cycles per distributor period. The duty cycle of a clock signal is defined as the percentage of the clock period during which a clock signal remains at one. The dwell angle is simply a measure of the clock duty cycle of the coil charging current. Using the same example, the clock duty cycle would be measured as (38° ÷ 60°) ×100% = 63.3%.

A dwell meter is simply a glorified clock duty cycle meter: it measures the duty cycle of the periodic charging signal at the primary winding of the ignition coil. The dwell angle is then computed as:

Dwell Angle = (Clock Duty Cycle × 360°) ÷ (Number of Cylinders)

This is why a dwell meter requires the user to select the number of cylinders for the ignition system under measurement.

Copyright © 2008 – 2012 Waqas Akram. All Rights Reserved.

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