Why do mobile applications crash?

Mobile devices have become an indispensable part of our everyday lives, mastering our on-line transactions and influencing our communication with others. However, most smartphone users experience application crashes once in a while. A crash manifests when, for example, you are using your favorite application and it suddenly stops working properly or closes. Sometimes, this can be really troublesome, especially when you try to send an important message or proceed with a financial transaction. There are many reasons that can lead mobile applications to crashes—and the causes are not always tractable. This blog entry discusses the causes of application crashes in mobile devices, based on the examination of a corpus of crash reports from Android applications [1].

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K-8 Computer Science Education

Technology has such a ubiquitous role in the world that kids are starting to use it at the age of two. These are, or rather will be, the so-called Digital Natives. These infant natives teach their grandparents how to use their iPads and iPhones with ease. This demonstrates how plastic the brain is during early stages of development. And if they are capable of using and teaching technology, kids are capable of understanding technology. Yet for many students, their first experiences in formal computer science classes begin in high school – if they’re lucky. So why do we open up the world of technology to kids at such an early age but not enable them to truly learn about it for years? It would be beneficial to education and society for schools to implement computer science curricula in K-8 education.

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My $300 Home Cloud Server: A Story of Blood, Sweat, and eBay

“I really wish I had a dedicated Linux computer to run computer vision algorithms on,” said my fiancée a couple of weeks ago. If you were there you would have been blinded by the metaphorical light bulb that lit over my head. You see, just the week before, my friend and co-worker had ordered an old, decommissioned (complete with “non-classified” stickers!) Apple Xserve off of eBay for merely $40. Like my fiancée, he wanted to have a machine for a special purpose: test compilations of open source software on a big-endian architecture. I was quite envious that he was able to hack on such cool hardware for such a cheap price. But, I wasn’t yet ready to bring out my wallet. I couldn’t justify indulging a new hobby without good reason—I was stuck waiting for just the right impetus. I didn’t wait long. My fiancée’s wish became my command!
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Parallel Programming through Dependence Analysis – Part I

 “As soon as an Analytical Engine exists, it will necessarily guide the future course of the science. Whenever any result is sought by its aid, the question will then arise — by what course of calculation can these results be arrived at by the machine in the shortest time?”

Charles Babbage (1864)

Points to Ponder

Would it not be wonderful, if we could write all our simulations as serial programs, and parallelized code (highly optimized for any given supercomputer) would be generated automatically by the compiler? Why is this not the case today? How come supercomputing centers require teams of highly trained developers to write simulations?


Scientists around the world develop mathematical models and write simulations to understand systems in nature. In many cases, simulation performance becomes an issue either as datasets (problem size) get larger, and/or when higher accuracy is required. In order to resolve the performance issues, parallel processing resources can be utilized. Since a large number of these simulations are developed using high level tools such as Matlab, Mathematica, Octave, etc., the obvious choice for the scientist is to use the parallel processing functions provided within the tool. A case in point is the parfor function in Matlab, which executes iterations of a for-loop in parallel. However, when an automation tool fails to parallelize a for-loop, it can be hard to understand why parallelization failed, and how one might change the code to help the tool with parallelization. Continue reading

Class participation incentive using e-tokens.

For the past two years I was the lab assistant for the “Information Systems Design and Implementation — Programming in Java” course, taught by my PhD supervisor Prof. Diomidis Spinellis at the Athens University of Economics and Business. To make the lesson more interesting and give an extra motivation to the students, me, Vassilios Karakoidas and Diomidis decided to distribute e-tokens to the students that actively participated. In return, the students were offered the possibility to better their grades by the end of the semester. In this post I will describe how we did this and I will provide some initial results based on the students feedback.

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Programming != Computer Science

For most students, computer science means lots of high-level coding, screens with black backgrounds and green text, and an esoteric subject. When students hear the term computer science, many think about programming languages – Java, C++, Python to name a few. However, what those students are really thinking about is computer programming, an extension and application of computer science. Computer science uses code and programming languages and different numerical systems, but computer science itself is the study of logic, efficiency, and problem solving. With that, it is worth examining what the world of computer science truly encompasses and what purposes it serves to study computer science.
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API Evaluation

API is the initials of “Application Programming Interface”. APIs are bundles of interfaces that developers must implement to build their applications. Common APIs are the Java, Python, and Ruby APIs, as well as the Android, iOS APIs and many other third-party libraries (e.g. jQuery and Google maps). Except for their source code, APIs come with their documentation. Then, client developers, from different programming levels, read this documentation to build distinct applications that use the same APIs. This means that an API should be unambiguous and useful in order to prevent developers from writing applications susceptible to crashes.

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Open Source in Education

As mentioned in a previous post by Maria Kechagia, “Free, Libre and Open Source Software (FLOSS) is software released under a license that allows developers to: 1) access the software’s source code, 2) use the software for free, and 3) develop derived works based on software’s previous releases.” FLOSS software is very versatile and can be used for a variety of purposes. One such purpose is education and institutional learning, a world in which software and technology is prevalent. However, at the present day institutions of learning (i.e., from high school up to university) mostly use commercial software such as Microsoft Office and Adobe Photoshop. Meanwhile, open source software such as OpenOffice, GIMP, and Linux offer the same capabilities as their commercial counterparts, yet are not employed as much. Weighing the options, it becomes clear that educational institutions should move to using more FLOSS software. Why? Let’s review the benefits for students.
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How Connected are Quantum Graphs?

Some students in my department this quarter hosted a reading group on quantum computing. Quantum computing is becoming more and more relevant and the topic attracted the participation of a diverse group of researchers. The best way to handle the scope of the topic and diversity of the participants was to invite volunteer speakers to give talks on the quantum analog of their own research area — “Quantum Circuit Lower Bounds,” “Quantum Game Theory,” and “QPSPACE” were among some of the topics. Naturally, I saw this as a great opportunity to understand more about quantum spectral graph theory. In this post I will outline some basic definitions and properties of quantum graphs, and as a follow up to my previous post on the connections between spectral geometry and graph theory, discuss isospectral properties of discrete and quantum graphs. Continue reading

Why to Get Involved in the Open Source Community?

Free, Libre and Open Source Software (FLOSS) is software released under a license that allows developers to: 1) access the software’s source code, 2) use the software for free, and 3) develop derived works based on software’s previous releases. FLOSS’s success can be attributed to the motivations of the individuals that are members of the open source community. However, FLOSS’s recent boom is also associated with the adoption of many business models, which rely on FLOSS, by modern companies. The aim of this post is to summarize the reasons that make individuals and companies to participate in the open source community and highlight the impact of FLOSS projects on computer science. To name some of the most popular FLOSS projects, consider: the Eclipse IDE, the Firefox browser, the Apache server, the Linux kernel, the Java, C/C++, Python programming languages, the MySQL, SQLite, PostgreSQL databases, the GNOME and KDE desktop environments, the Git version control system, the R-Project for statistical computing, the TeX system for publishing, etc.

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