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• How should I Test a Genetic Algorithm

  - by James Brooks

  I have made a quite few genetic algorithms; they work (they find a reasonable solution quickly). But I have now discovered TDD. Is there a way to write a genetic algorithm (which relies heavily on random numbers) in a TDD way? To pose the question more generally, How do you test a non-deterministic method/function. Here is what I have thought of: Use a specific seed. Which wont help if I make a mistake in the code in the first place but will help finding bugs when refactoring. Use a known list of numbers. Similar to the above but I could follow the code through by hand (which would be very tedious). Use a constant number. At least I know what to expect. It would be good to ensure that a dice always reads 6 when RandomFloat(0,1) always returns 1. Try to move as much of the non-deterministic code out of the GA as possible. which seems silly as that is the core of it's purpose. Links to very good books on testing would be appreciated too.

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• How to make developers follow coding standards?

  - by Josh

  How can I make developers follow coding standards? In our company: I've given documents and they don't have the patience to read it and follow it. I've tried telling them again and again "please do it this way" they nod their heads, but still do it the wrong way We're doing a project for the third time and still they don't seem to follow it properly. I'm now so tired of this. What is the best way to set standards for coding and make sure they follow them? Edit: There are just about 10 developers in my team. They're over pressurized and do not take the time to put comments and do the code neatly since there's more pressure to complete the product from our management. What would be the solution for this?

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• What do you mean by the expressiveness in a programming language?

  - by prosseek

  I see a lot of the word 'expressiveness' when people want to stress one language is better than the other. But I don't see exactly what they mean by it. Is it the verboseness/succinctness? I mean, if one language can write down something shorter than the other, does that mean expressiveness? Please refer to my other question - http://stackoverflow.com/questions/2411772/article-about-code-density-as-a-measure-of-programming-language-power Is it the power of the language? Paul Graham says that one language is more powerful than the other language in a sense that one language can do that the other language can't do (for example, LISP can do something with macro that the other language can't do). Is it just something that makes life easier? Regular expression can be one of the examples. Is it a different way of solving the same problem: something like SQL to solve the search problem? What do you think about the expressiveness of a programming language? Can you show the expressiveness using some code? What's the relationship with the expressiveness and DSL? Do people come up with DSL to get the expressiveness?

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• Code Golf: 1x1 black pixel

  - by Joey Adams

  Recently, I used my favorite image editor to make a 1x1 black pixel (which can come in handy when you want to draw solid boxes in HTML cheaply). Even though I made it a monochrome PNG, it came out to be 120 bytes! I mean, that's kind of steep. 120 bytes. For one pixel. I then converted it to a GIF, which dropped the size down to 43 bytes. Much better, but still... Challenge The shortest image file or program that is or generates a 1x1 black pixel. A submission may be: An image file that represents a 1x1 black pixel. The format chosen must be able to represent larger images than 1x1, and cannot be ad-hoc (that is, it can't be an image format you just made up for code golf). Image files will be ranked by byte count. A program that generates such an image file. Programs will be ranked by character count, as usual in code golf. As long as an answer falls into one of these two categories, anything is fair game.

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• Best ways to teach a beginner to program?

  - by Justin Standard

  Original Question I am currently engaged in teaching my brother to program. He is a total beginner, but very smart. (And he actually wants to learn). I've noticed that some of our sessions have gotten bogged down in minor details, and I don't feel I've been very organized. (But the answers to this post have helped a lot.) What can I do better to teach him effectively? Is there a logical order that I can use to run through concept by concept? Are there complexities I should avoid till later? The language we are working with is Python, but advice in any language is welcome. How to Help If you have good ones please add the following in your answer: Beginner Exercises and Project Ideas Resources for teaching beginners Screencasts / blog posts / free e-books Print books that are good for beginners Please describe the resource with a link to it so I can take a look. I want everyone to know that I have definitely been using some of these ideas. Your submissions will be aggregated in this post. Online Resources for teaching beginners: A Gentle Introduction to Programming Using Python How to Think Like a Computer Scientist Alice: a 3d program for beginners Scratch (A system to develop programming skills) How To Design Programs Structure and Interpretation of Computer Programs Learn To Program Robert Read's How To Be a Programmer Microsoft XNA Spawning the Next Generation of Hackers COMP1917 Higher Computing lectures by Richard Buckland (requires iTunes) Dive into Python Python Wikibook Project Euler - sample problems (mostly mathematical) pygame - an easy python library for creating games Create Your Own Games With Python ebook Foundations of Programming for a next step beyond basics. Squeak by Example Recommended Print Books for teaching beginners Accelerated C++ Python Programming for the Absolute Beginner Code by Charles Petzold

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• Converting EBNF to BNF

  - by Vivin Paliath

  It's been a few years since my computer-language class and so I've forgotten the finer points of BNF's and EBNF's and I don't have a textbook next to me. Specifically, I've forgotten how to convert an EBNF into BNF. From what little I remember, I know that one of the main points is to convert { term } into <term> | <many-terms>. But I don't remember the other rules. I've tried to look this up online but I can only find links to either homework questions, or a small comment about converting terms with curly braces. I can't find an exhaustive list of rules that define the translation.

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• Code Golf - p day

  - by gnibbler

  The Challenge The shortest code by character count to display a representation of a circle of radius R using the *character, followed by an approximation of p. Input is a single number, R. Since most computers seem to have almost 2:1 ratio you should only output lines where y is odd. The approximation of p is given by dividing twice the number of * characters by R². The approximation should be correct to at least 6 significant digits. Leading or trailing zeros are permitted, so for example any of 3, 3.000000, 003 is accepted for the inputs of 2 and 4. Code count includes input/output (i.e., full program). Test Cases Input 2 Output *** *** 3.0 Input 4 Output ***** ******* ******* ***** 3.0 Input 8 Output ******* ************* *************** *************** *************** *************** ************* ******* 3.125 Input 10 Output ********* *************** ***************** ******************* ******************* ******************* ******************* ***************** *************** ********* 3.16

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• Why are copy constructors unnecessary for immutable objects?

  - by Jothi

  Why are copy constructors unnecessary for immutable objects? Please explain this for me.

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• Obtaining IP addresses in Bittorrent

  - by Legend

  I am trying to get a list of IP addresses serving or downloading a file. What I did was to contact a tracker like openbittorrent.com to get the following (as part of the scrape file): B%00%00%0C%5F%B1%B1l%CAGa%84S%CB%B0%9BG%84%3BE:0:1 Now, the long string in the beginning is the info hash. As a next step, I did this: http://tracker.sometracker.com/announce?info_hash=B%00%00%0C%5F%B1%B1l%CAGa%84S%CB%B0%9BG%84%3BE It gave me back the following. So far so good. The message contained this: d8:completei0e10:downloadedi0e10:incompletei2e8:intervali1931e12:min intervali965e5:peers12:U????????^@^@e Can someone tell me what should I be doing after this to get the IP addresses currently serving the file or downloading it?

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• Code Golf - PI day

  - by gnibbler

  The Challenge The shortest code by character count to display a representation of a circle of radius R using the *character. Followed by an approximation of pi Input is a single number, R Since most computers seem to have almost 2:1 ratio you should only output lines where y is odd. The approximation of pi is given by dividing the twice the number of * characters by R squared. The approximation should be correct to at least 6 significant digits. Leading or trailing zeros are permitted, so for example any of 3,3.000000,003 is accepted for the inputs of 2 and 4 Code count includes input/output (i.e full program). Test Cases Input 2 Output *** *** 3.0 Input 4 Output ***** ******* ******* ***** 3.0 Input 8 Output ******* ************* *************** *************** *************** *************** ************* ******* 3.125 Input 10 Output ********* *************** ***************** ******************* ******************* ******************* ******************* ***************** *************** ********* 3.16

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• Properties of bad fibonacci algorithm

  - by John Smith

  I was looking at the canonical bad fibonacci algorithm the other day: public static int fib(int n) { // Base Case if (n < 2) return 1; else return fib(n-1) + fib(n-2); } I made the interesting observation. When you call fib(n), then for k between 1 and n fib(k) is called precisely fib(n-k+1) times (or fib(n-k) depending on your definition of fib(0) ). Also, fib(0) is called fib(n-k-1) times. This then allows me to find that in fib(100) there are exactly 708449696358523830149 calls to the fib function. Are there other interesting observations on this function you know of?

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• What problems have you solved using artificial neural networks?

  - by knorv

  I'd like to know about specific problems you - the SO reader - have solved using artificial neural network techniques and what libraries/frameworks you used if you didn't roll your own. Questions: What problems have you used artificial neural networks to solve? What libraries/frameworks did you use? I'm looking for first-hand experiences, so please do not answer unless you have that.

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• Is recursion ever faster than looping?

  - by Carson Myers

  I know that recursion is sometimes a lot cleaner than looping, and I'm not asking anything about when I should use recursion over iteration, I know there are lots of questions about that already. What I'm asking is, is recursion ever faster than a loop? To me it seems like, you would always be able to refine a loop and get it to perform more quickly than a recursive function because the loop is absent constantly setting up new stack frames. I'm specifically looking for whether recursion is faster in applications where recursion is the right way to handle the data, such as in some sorting functions, in binary trees, etc.

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• Push DVCS repository to master without needing codebase

  - by Scorchin

  To work on a client's staging environment I have to connect through a VPN which locks all normal network traffic and prevents any connection to the Internet. This would immediately prevent any of the "normal" VCS solutions from being used as it's not possible to gain access to the server. A solution to this would be to create a DVCS repository (git?) locally and then push changes to the master, as and when needed. There is one flaw in this plan. The entire codebase is around 14GB. To download all of this over the internet would take some time, especially when I'm likely to be working on 3 or 4 different machines in each case. This seems silly and overkill for a DVCS. TL;DR Can any DVCS solution allow you to push to a master server/repo without needing the codebase? Bad example: copy the .git folder (not the 14GB codebase) to another directory and push this to the master once disconnected from the VPN.

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• What's the best name for a non-mutating "add" method on an immutable collection?

  - by Jon Skeet

  Sorry for the waffly title - if I could come up with a concise title, I wouldn't have to ask the question. Suppose I have an immutable list type. It has an operation Foo(x) which returns a new immutable list with the specified argument as an extra element at the end. So to build up a list of strings with values "Hello", "immutable", "world" you could write: var empty = new ImmutableList<string>(); var list1 = empty.Foo("Hello"); var list2 = list1.Foo("immutable"); var list3 = list2.Foo("word"); (This is C# code, and I'm most interested in a C# suggestion if you feel the language is important. It's not fundamentally a language question, but the idioms of the language may be important.) The important thing is that the existing lists are not altered by Foo - so empty.Count would still return 0. Another (more idiomatic) way of getting to the end result would be: var list = new ImmutableList<string>().Foo("Hello"); .Foo("immutable"); .Foo("word"); My question is: what's the best name for Foo? EDIT 3: As I reveal later on, the name of the type might not actually be ImmutableList<T>, which makes the position clear. Imagine instead that it's TestSuite and that it's immutable because the whole of the framework it's a part of is immutable... (End of edit 3) Options I've come up with so far: Add: common in .NET, but implies mutation of the original list Cons: I believe this is the normal name in functional languages, but meaningless to those without experience in such languages Plus: my favourite so far, it doesn't imply mutation to me. Apparently this is also used in Haskell but with slightly different expectations (a Haskell programmer might expect it to add two lists together rather than adding a single value to the other list). With: consistent with some other immutable conventions, but doesn't have quite the same "additionness" to it IMO. And: not very descriptive. Operator overload for + : I really don't like this much; I generally think operators should only be applied to lower level types. I'm willing to be persuaded though! The criteria I'm using for choosing are: Gives the correct impression of the result of the method call (i.e. that it's the original list with an extra element) Makes it as clear as possible that it doesn't mutate the existing list Sounds reasonable when chained together as in the second example above Please ask for more details if I'm not making myself clear enough... EDIT 1: Here's my reasoning for preferring Plus to Add. Consider these two lines of code: list.Add(foo); list.Plus(foo); In my view (and this is a personal thing) the latter is clearly buggy - it's like writing "x + 5;" as a statement on its own. The first line looks like it's okay, until you remember that it's immutable. In fact, the way that the plus operator on its own doesn't mutate its operands is another reason why Plus is my favourite. Without the slight ickiness of operator overloading, it still gives the same connotations, which include (for me) not mutating the operands (or method target in this case). EDIT 2: Reasons for not liking Add. Various answers are effectively: "Go with Add. That's what DateTime does, and String has Replace methods etc which don't make the immutability obvious." I agree - there's precedence here. However, I've seen plenty of people call DateTime.Add or String.Replace and expect mutation. There are loads of newsgroup questions (and probably SO ones if I dig around) which are answered by "You're ignoring the return value of String.Replace; strings are immutable, a new string gets returned." Now, I should reveal a subtlety to the question - the type might not actually be an immutable list, but a different immutable type. In particular, I'm working on a benchmarking framework where you add tests to a suite, and that creates a new suite. It might be obvious that: var list = new ImmutableList<string>(); list.Add("foo"); isn't going to accomplish anything, but it becomes a lot murkier when you change it to: var suite = new TestSuite<string, int>(); suite.Add(x => x.Length); That looks like it should be okay. Whereas this, to me, makes the mistake clearer: var suite = new TestSuite<string, int>(); suite.Plus(x => x.Length); That's just begging to be: var suite = new TestSuite<string, int>().Plus(x => x.Length); Ideally, I would like my users not to have to be told that the test suite is immutable. I want them to fall into the pit of success. This may not be possible, but I'd like to try. I apologise for over-simplifying the original question by talking only about an immutable list type. Not all collections are quite as self-descriptive as ImmutableList<T> :)

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• Derived class linker - is this wrong?

  - by bobobobo

  We have this situation: A B ^ ^ | / C so class A { } class B { } class C : public A, public B { } Now, B wants to access a property in C. How do you do this? The solution I came up with is to place a pointer in B to an instance of C, which is only active (not null) if this B is in fact a C.

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• Tips on a tool to measure code quality?

  - by Cristi Diaconescu

  I'm looking for a tool that can provide code quality metrics. For instance it could report very long functions (spaghetti code) very complex classes (which could contain do-it-all code) ... While we're on the (subjective:-) subject of code quality, what other code metrics would you suggest? I'm targetting C#/.NET code, but I'm sure this could extend to most programming languages.

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• Tracking Google Analytics events with server side request automation

  - by Esko

  I'm currently in the process of programming an utility which generates GA tracking pixel (utm.gif) URL:s based on given parameters. For those of you who are wondering why I'm doing this on the server side, I need to do this server side since the context which I'm going to start tracking simply doesn't support JavaScript and as such ga.js is completely useless to me. I have managed to get it working otherwise quite nicely but I've hit a snag: I can't track events or custom variables because I have no idea how exactly the utme parameter's value should be structured to form a valid event or var type hit. GA's own documentation on this parameter isn't exactly that great, either. I've tried everything from Googling without finding anything (which I find ironic) to reverse engineering ga.js, unfortunately it's minified and quite unreadable because of that. The "mobile" version of GA didn't help either since officially GA mobile doesn't support events nor vars. To summarize, what is the format of the utme parameter for page hit types event and custom variable?

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• Fix common library functions, or abandon then?

  - by Ian Boyd

  Imagine i have a function with a bug in it: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" return City+", "+State; } So the call: MakeLocation("Springfield", "MO"); would return "Springfield, MO" Now there's a slight problem, what if the user called: MakeLocation("Springfield, MO", "OH"); The called it wrong, obviously. But the function would return "Springfield, MO, OH". The system was functioning like this for many years, until i noticed the function being used wrong, and i corrected it. And i also updated the original function to catch such an obvious mistake - in case it's happening elsewhere: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" if (City.Contains, ",") throw new EMakeLocationException("City name contains a comma. You probably didn't mean that"); return City+", "+State; } And testing showed the problem fixed. Except we missed an edge case, and the customer found it. So now the moral dillema. Do you ever add new sanity checks, safety checks, assertions to exising code? Or do you call the old function abandoned, and have a new one: Boolean MakeLocation(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" return City+", "+State; } Boolean MakeLocation2(String City, String State) { //Given "Springfield", "MO" //return "Springfield, MO" if (City.Contains, ",") throw new EMakeLocationException("City name contains a comma. You probably didn't mean that"); return City+", "+State; } The same can apply for anything: Question FetchQuestion(Int id) { if (id == 0) throw new EFetchQuestionException("No question ID specified"); ... } Do you risk breaking existing code, at the expense of existing code being wrong?

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• Code Golf: MSM Random Number Generator

  - by Vivin Paliath

  The challenge The shortest code by character count that will generate (pseudo)random numbers using the Middle-Square Method. The Middle-Square Method of (pseudo)random number generation was first suggested by John Von Neumann in 1946 and is defined as follows: Rn+1 = mid((Rn)2, m) For example: 34562 = 11943936 mid(11943936) = 9439 94392 = 89094721 mid(89094721) = 0947 9472 = 896809 mid(896809) = 9680 96802 = 93702400 mid(93702400) = 7024 Test cases: A seed of 8653 should give the following numbers (first 10): 8744, 4575, 9306, 6016, 1922, 6940, 1636, 6764, 7516, 4902

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• How to convert floats to human-readable fractions?

  - by Swaroop C H

  Let's say we have 0.33, we need to output "1/3". If we have "0.4", we need to output "2/5". The idea is to make it human-readable to make the user understand "x parts out of y" as a better way of understanding data. I know that percentages is a good substitute but I was wondering if there was a simple way to do this?

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• Best non-development book for software developers

  - by Dima Malenko

  What is the best non software development related book that you think each software developer should read? Note, there is a similar, poll-style question here: What non-programming books should programmers read? Update: Peopleware is a great book, must read, no doubt. But it is about software development so does not count. Update: We ended up suggesting more than one book and that's great! Below is summary (with links to Amazon) of the books you should consider for your reading list. The Design of Everyday Things by Donald Norman Getting Things Done by David Allen Godel, Escher, Bach by Douglas R. Hofstadter The Goal and It's Not Luck by Eliyahu M. Goldratt Here Comes Everybody by Clay Shirky ...to be continued.

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• Do you have genetic algorithm in production?

  - by Max

  Is it good idea to use genetic algorithm in production? If you are using it: In what case? What pros for selecting subj? Can you easily add changes to algorithm?

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• Is there a website to lookup common, already written functions?

  - by pinnacler

  I'm sitting here writing a function that I'm positive has been written before, somewhere on earth. It's just too common to have not been attempted, and I'm wondering why I can't just go to a website and search for a function that I can then copy and paste into my project in 2 seconds, instead of wasting my day reinventing the wheel. Sure there are certain libraries you can use, but where do you find these libraries and when they are absent, is there a site like I'm describing? Possibly a wiki of some type that contains free code that anybody can edit and improve?

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• pass by reference or pass by value?

  - by Sven

  When learning a new programming language, one of the possible roadblocks you might encounter is the question whether the language is, by default, pass-by-value or pass-by-reference So here is my question to all of you, in your favorite language, how is it actually done? and what are the possible pitfalls? your favorite language can, of course, be anything you have ever played with: popular, obscure, esoteric, new, old ...

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