tag:blogger.com,1999:blog-62574281386445826992025-07-21T15:39:23.427+03:00searching everywhere...Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.comBlogger62125tag:blogger.com,1999:blog-6257428138644582699.post-35473053307438401412016-01-23T09:21:00.000+02:002016-01-23T09:29:53.723+02:00

I just finished working on a banner for my univeristy. The design involves three logos for the three entities involved in this activity: the school mascot, the student organization and the house of representatives. I preferred the mascot vs the seal since I believe it's more natural for students to identify with. And to keep things light and informal I also preferred an easily recognizable

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com1tag:blogger.com,1999:blog-6257428138644582699.post-41066253656913507842015-11-29T05:56:00.000+02:002016-04-24T21:01:45.406+02:00

MathJax.Hub.Config({tex2jax: {inlineMath: [['$','$'], ['\\(','\\)']]}}); This came up a week or so ago in a discussion with a lab mate. The governing principle is well-known from physics, but I was too lazy to find a derivation online. Later on, I had an idea and wanted to give it a try, so here goes. We're interested in the shortest path starting at point $a$ to point $b$ with the

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-26387332505734987512014-03-23T19:06:00.001+02:002014-03-23T19:06:50.421+02:00

I've done this task once before and forgot how. It took me a while to do it again, so I'm posting this here in case somebody else needs it. It might not be the best way to do it so if you can make it better, I'd love to hear from you. I'm using pstill_dist and pdfcrop with two subdirectories for all input and output files. #!/bin/bash for FILE in $(find ./input -name '*.ps'); do

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-66145770544176987302011-05-08T07:02:00.017+02:002014-09-17T22:12:17.181+03:00

College students spend lots of time on Facebook and virtually use it to share and organize their shcedules and course materials. Obviously, things get out of control and you end up with a very long and entangled feed that you might find yourself in a real need to explore or even worse, scan for something important. So, one day a student of mine posted (!), wondering if there were any group

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com21tag:blogger.com,1999:blog-6257428138644582699.post-75730845424310420422011-01-26T14:55:00.006+02:002011-01-26T15:38:09.039+02:00

I got myself into a situation where I really wished that Java collections accepted a visitor interface of some kind so I could define one on the fly and get my job done. Alas, I decided to implement the utility myself and here's the result.public interface IVisitor<T> { void visit(T item);}public class CollectionUtils { public static<T> void applyVisitor(Collection<T> collection

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com2tag:blogger.com,1999:blog-6257428138644582699.post-30102518469363058352010-10-24T23:48:00.007+02:002010-10-25T00:51:59.286+02:00

Population count is the number of '1' bits in the binary representation of an integer.The basic trick we employ is to get the next higher number with the same number of 1-bits, which we borrow from the Hacker's Delight (whole book). Below is a Java implementation of all 4 version of the snoob function.public static int snoob1(int x) { int r = x + (x & -x); return r | ((x ^ r) >>> (2 +

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-89149706605500199242010-07-17T15:32:00.005+03:002010-07-17T15:58:28.334+03:00

Below is a Java port of the algorithm by James McCaffrey as presented in the MSDN article Generating the mth Lexicographical Element of a Mathematical Combination.Please do take into consideration that this implementation only uses int as Java does not allow array indexing with long. This means that the valid input range is more restricted. Watch out for overflows!/** * Based on the Combinadic

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com3tag:blogger.com,1999:blog-6257428138644582699.post-78667807642473136332010-06-21T06:48:00.011+03:002010-07-21T00:21:22.042+03:00

In this post, we present an object-oriented design and implementation of an event-driven G/G/1 queue model simulation using Java. The lecture notes on Computer System Analysis by Raj Jain were very helpful and are highly recommended. In particular, we would like to reference the introductory lectures on Simulation Modeling and Queueing Theory.Please note that this implementation is provided as a

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com3tag:blogger.com,1999:blog-6257428138644582699.post-41050088396053994172010-04-28T07:17:00.007+02:002010-04-29T17:56:51.981+02:00

I've been using Google Analytics for 2 years to track the traffic on this blog. It's really interesting to see which posts receive more attention and what traffic sources and keywords generated how much traffic on any one day. This is specially important to me since the majority of the traffic to my blog comes from search engines a.k.a. google (organic).However, when you really look into the

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-8070841438246907612010-02-05T00:44:00.007+02:002010-02-10T01:14:49.145+02:00

Google App Engine lets you run your web applications on Google's infrastructure e.g. GFS and BigTable. App Engine applications are easy to build, easy to maintain, and easy to scale as your traffic and data storage needs grow. With App Engine, there are no servers to maintain: You just upload your application, and it's ready to serve your users... more docs. An alternative introduction is

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-65819531603003090712010-01-28T07:15:00.008+02:002011-08-26T03:24:20.935+02:00

In this post, we'll use our PhoneNumberFormatter to implement an auto-formatting phone number text field in an attempt to mimic the behavior of iPhone's native apps, like Phone and Contacts. So, let's call the text field in question myTextField. We start by calling addTarget on the text field to make it call the autoFormatTextField method in our view controller whenever it gets updated, either

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com15tag:blogger.com,1999:blog-6257428138644582699.post-32539015155609884512010-01-23T06:46:00.011+02:002011-09-10T10:13:41.476+02:00

Reservoir sampling is a family of randomized algorithms for randomly choosing K samples from a list of S items, where S is either a very large or unknown number.A very elegant algorithm titled Algorithm R by Alan G. Waterman, is summarized as follows:Fill up the 'reservoir' with the first k items from SFor every item S[j] where j > K Choose an integer r between 0 and j If r < K then replace

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-84206757340411855432010-01-22T14:38:00.031+02:002015-02-06T23:19:21.359+02:00

iPhone developers often find themselves trying to stick to the standards set by Apple. Most of the time, doing so is facilitated by the SDK and the results are better. Sometimes though, it's not easy at all, mainly because some APIs are not open. One example is phone number formatting. The Contacts application utilizes an auto-formatting UITextField for phone number entry. Many business

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com22tag:blogger.com,1999:blog-6257428138644582699.post-41412495524101963552010-01-22T13:39:00.008+02:002010-01-23T16:54:35.158+02:00

I wanted to simulate the situation when the server doesn't respond, without changing much. A friend of mine suggested I use any of the unassigned IPs on our LAN. Exactly what I was looking for! The request timed-out and I was able to see how my application would act in this case. We may also add an entry in the hosts file to name this black-hole-server, so it can be used later as needed. The

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-79829206084247110522010-01-14T01:35:00.004+02:002012-11-18T11:52:58.956+02:00

A friend of mine recommended this video and I liked it so much I shared it immediately with other friends. As some of them were very busy to watch the whole thing, they asked for a summary. And since the topic was still active on my mind, I decided to do it for them and later I decided to make it available to everybody on this blog.I have to emphasize that this text is based entirely and solely

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-2615732621443618162009-12-31T00:05:00.017+02:002010-05-10T18:22:44.544+03:00

Using a Discrete Wiener Process Acceleration (DWPA) model, we illustrate the usage of the Java implementation of the Kalman filter we presented in the previous post. The model we employ here is taken from Estimation with Applications to Tracking and Navigation.We start by building the Kalman filter using this method:public static KalmanFilter buildKF(double dt, double processNoisePSD, double

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com12tag:blogger.com,1999:blog-6257428138644582699.post-19863161464719070152009-12-06T00:28:00.010+02:002010-05-10T18:21:22.710+03:00

This is a very clear and straight forward implementation of the Discrete Kalman Filter Algorithm in the Java language using the JAMA package. I wrote this code for testing and simulation purposes.import Jama.Matrix;/** * This work is licensed under a Creative Commons Attribution 3.0 License. * * @author Ahmed Abdelkader */public class KalmanFilter { protected Matrix X, X0; protected Matrix F, B,

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com4tag:blogger.com,1999:blog-6257428138644582699.post-55198702834210031992009-12-03T19:10:00.004+02:002009-12-04T04:44:04.180+02:00

I wanted to parse some simple XML response from a server and I really wouldn't bother to use NSXMLParser or libxml2 as discussed here on stackoverflow. I get a single node and I just wanted to get the content. I ended up with this utility method:+ (NSString *)xmlNodeContent:(NSData *)xmlData { NSString *node = [[NSString alloc] initWithData:xmlData encoding:NSUTF8StringEncoding]; NSString *

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-43476914731811837232009-11-23T20:01:00.009+02:002011-09-10T09:51:15.693+02:00

No need for UITextViews or custom UITableViewCells. You can use standard UITableViewCellStyles and make the detailTextLabel accept multiple lines and specify its line break mode. The code would be:static NSString *CellIdentifier = @"MyCell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];if (cell == nil) { cell = [[[UITableViewCell alloc]

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com15tag:blogger.com,1999:blog-6257428138644582699.post-49849162027211462002009-11-12T21:26:00.011+02:002009-11-23T20:01:43.132+02:00

I had a UIViewController with a couple of UITextFields attached to its default UIView and everything was fine. Later on, I added a couple more text fields, so I had to make sure all text fields are displayed properly when the keyboard shows up. I thought about using a UIScrollView or maybe a UITableView which scrolls naturally, but I thought I didn't have to change my controller just for that. I

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-86314975467823750442009-05-05T03:19:00.007+03:002009-05-05T04:35:46.072+03:00

FluTracker is a website that tracks the progress of swine flu using data from official sources, news reports and user-contributions*. The site was built using technology provided by Rhiza Labs and Google. This post on Mashable also has great information about tracking swine flu online.Tracking epidemics was one of the first applications of geospatial information. In 1854, John Snow depicted a

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-40340947834948748532009-04-28T23:22:00.006+03:002014-11-21T05:42:57.767+02:00

import Jama.Matrix; import Jama.SingularValueDecomposition; public class Matrices { /** * The difference between 1 and the smallest exactly representable number * greater than one. Gives an upper bound on the relative error due to * rounding of floating point numbers. */ public static double MACHEPS = 2E-16; /** * Updates MACHEPS for the executing machine. */ public static void

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com13tag:blogger.com,1999:blog-6257428138644582699.post-19889310460255458712009-01-22T10:00:00.005+02:002009-01-23T03:22:08.956+02:00

I was really pissed off when I read about the new antitrust charges Microsoft is facing from the EU. It was mentioned in the news article published under "EU: Microsoft 'shields' IE from competition" how EU looks at the case:The evidence gathered during the investigation leads the commission to believe that the tying of Internet Explorer with Windows, which makes Internet Explorer available on 90

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0tag:blogger.com,1999:blog-6257428138644582699.post-85830642947398260292009-01-14T15:01:00.007+02:002009-02-02T01:29:14.530+02:00

I was looking for a free program to help me simulate Wi-Fi signal propagation for indoor environments. I wanted a program that could take a floor map and do some ray tracing or apply some known propagation model. I was disappointed when I couldn't find any open source software in that area. All the free programs I found were very naive and targeted radio hobbyists. On the other hand, I found a

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com11tag:blogger.com,1999:blog-6257428138644582699.post-19084431106536831442009-01-07T13:36:00.007+02:002009-01-07T14:29:23.168+02:00

A couple of days ago, I was working on a J2EE project using EJB 3.0 and plain JSP/Servlets. I used Netbeans 6.0.1 with GlassFish 9.1 on my XP Professional PC. For some reason, the project build kept on failing, without any changes in the configuration files which I barely touched. After digging through the stack traces and log files I got, I found this message "The ResourceConfig instance does

Ahmed Abdelkaderhttp://www.blogger.com/profile/01141303576931872803noreply@blogger.com0