Local Maxima in Edge Detection

I’ve been working on some homework for computer vision. It’s such an interesting class because of how rich the visualization of my code results can be. Matlab has also been a real pleasure to work with. Everything is well documented and the IDE has features I haven’t seen in other IDEs. I am working on […]

Matlab’s Image Edge Detection

I’ve been doing some homework for Computer Vision class. Matlab apparently has extensive image processing capabilities. One handy function is “edge” which will return a zero-filled matrix with 1s corresponding to edges.

Mobile JS Framework Comparison

I did a quick matrix to compare various mobile JS frameworks in late May. It is probably a little outdated, especially with the recent Sencha merger, and I did not know DashCode could create web applications at the time, but maybe it will help someone. Enjoy! //bit.ly/d6Gsaj

Scifihifi-iPhone Keychain Wrapper

Here’s a great wrapper that really simplifies working with KeyChain in iOS //log.scifihifi.com/post/55837387/simple-iphone-keychain-code. The code is on GitHub as well //github.com/ldandersen/scifihifi-iphone/tree/master/security/. Apple’s official documentation is here, and there is also a sample project, but it’s not a good example for getting up and running quickly. The version of the project (last updated 10/2009) doesn’t even […]

Invalid entitlements

I was having big issues deploying to an iPad from XCode tonight. There was an error concerning invalid entitlements. The executable was signed with invalid entitlements. The entitlements specified in your application’s Code Signing Entitlements file do not match those specified in your provisioning profile. (0xE8008016) I was able to fix this by making sure […]

Project Euler Problem 10 Solution: Clojure

Problem description, from Project Euler Find the sum of all the primes below N. Solution Brute-forced it again, but it still runs in less than 30 seconds (at least on my MacBook Pro). This one was simple using the Sieve of Eratosthenes from problem 7. The sieve, collapsed because it’s the same as from problem […]

Project Euler Problem 8 Solution: Clojure

Problem description, from Project Euler Find the greatest product of five consecutive digits in the 1000-digit number. 73167176531330624919225119674426574742355349194934 96983520312774506326239578318016984801869478851843 85861560789112949495459501737958331952853208805511 12540698747158523863050715693290963295227443043557 66896648950445244523161731856403098711121722383113 62229893423380308135336276614282806444486645238749 30358907296290491560440772390713810515859307960866 70172427121883998797908792274921901699720888093776 65727333001053367881220235421809751254540594752243 52584907711670556013604839586446706324415722155397 53697817977846174064955149290862569321978468622482 83972241375657056057490261407972968652414535100474 82166370484403199890008895243450658541227588666881 16427171479924442928230863465674813919123162824586 17866458359124566529476545682848912883142607690042 24219022671055626321111109370544217506941658960408 07198403850962455444362981230987879927244284909188 84580156166097919133875499200524063689912560717606 05886116467109405077541002256983155200055935729725 71636269561882670428252483600823257530420752963450 Solution I decided to store the data in a text file. Not only would it save me from […]

Project Euler Problem 9 Solution: Clojure

Problem description, from Project Euler There exists exactly one Pythagorean triplet for which a + b + c = N. (N is known.) Find the product abc. Solution This was a quick once since I just brute-forced it. I think there are some optimizations possible related to the idea that a^2 + b^2 < c^2. […]

Project Euler Problem 7 Solution: Clojure

Problem Description, from Project Euler What is the n-th prime number? Problem Solution This was simple to solve using the Sieve created for the solution to problem #3. To make the program variable, we start with finding all primes less than 1000. If that is not enough to solve the problem, we double this “maximum” […]

Sql Cross Apply

I found out about a feature in SQL Server 2005 I didn’t know about (having come from a SQL Server 2000 shop). Cross Apply! It’s for when you want to feed the value of a table row into a function and join on the results. This is different than a cross join, because you cannot […]

Project Euler Problem 4 Solution: Clojure

Problem Description, from Project Euler Find the largest palindrome made from the product of two 3-digit numbers Solution I couldn’t think of many optimizations for this problem, other than avoiding duplicates when calculating the products of numbers. That’s why I just brute-forced it. The only (barely) interesting thing I did here was to write a […]

Project Euler Problem 3 Solution: Clojure

Problem description, from Project Euler What is the largest prime factor of the number N? Solution In previous problems, I was using a list of primes I got somewhere else. I figured it would be relevant to implement a prime-finding algorithm. I decided to go with simplicity, and implement the Sieve of Eratosthenes. It’s basically […]

Project Euler Problem 6 Solution: Clojure

Problem description, from Project Euler Find the difference between the sum of the squares of the first N natural numbers and the square of the sum. Solution This one actually seemed to be easier than the others. No filters required! The biggest hangup I had was that when I originally read the problem, I thought […]

Project Euler Problem 5 Solution: Clojure

Problem description, from Project Euler What is the smallest number that is evenly divisible by all of the numbers from 1 to N? Solution The math Basically, we are finding the least common multiple (LCM) of the numbers (grade school math?). This can be done by generating the prime factors of each of the numbers. […]

Project Euler Problem 2 Solution: Clojure

Problem 2 Description, from Project Euler Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million. Solutions My first attempt The trickiest thing for me was figuring out how to write the fibonacci function in an elegant way. I know that with functional languages, recursion is supposed […]