Has anyone found reference to what type of algorithm GameplayKit uses for pathfinding? I have reviewed Apple's documentation and was not able to find anything.
Ultimately I am curious to its performance vs. A* implemented without GameplayKit. While I am sure Apple did an amazing job, I don't want to pay performance overhead for features I will not use.
I am also just curious because I enjoy learning about these types of mechanics.
Thanks,
E
Only Apple can say for sure. But the presence of methods for both cost and estimated-cost strongly suggests A*, or at least some variant on it with similar enough algorithmic complexity.
If you're really concerned about performance, though, set yourself up with some test cases and profile them. You can start with something like their Pathfinder sample code project... re-run pathfinding with lots of different mazes and see how the time (which is pretty darn short already) changes with maze size.
for a study on genetic programming, I would like to implement an evolutionary system on basis of llvm and apply code-mutations (possibly on IR level).
I found llvm-mutate which is quite useful executing point mutations.
As far as I have understood, the instructions get count/numbered, one can then e.g. delete a numbered instruction.
However, introduction of new instructions seems to be possible as one of the availeable statements in the code.
Real mutation however would allow to insert any of the allowed IR instructions, irrespective of it beeing used in the code to be mutated.
In addition, it should be possible to insert library function calls of linked libraries (not used in the current code, but possibly available, because the lib has been linked in clang).
Did I overlook this in the llvm-mutate or is it really not possible so far?
Are there any projects trying to /already have implement(ed) such mutations for llvm?
llvm has lots of code analysis tools which should allow the implementation of the afore mentioned approach. llvm is huge, so I'm a bit disoriented. Any hints which tools could be helpful (e.g. getting a list of available library functions etc.)?
Thanks
Alex
Very interesting question. I have been intrigued by the possibility of doing binary-level genetic programming for a while. With respect to what you ask:
It is apparent from their documentation that LLVM-mutate can't do what you are asking. However, I think it is wise for it not to. My reasoning is that any machine-language genetic program would inevitably face the "Halting Problem", e.g. it would be impossible to know if a randomly generated instruction would completely crash the whole computer (for example, by assigning a value to a OS-reserved pointer), or it might run forever and take all of your CPU cycles. Turing's theorem tells us that it is impossible to know in advance if a given program would do that. Mind you, LLVM-mutate can cause for a perfectly harmless program to still crash or run forever, but I think their approach makes it less likely by only taking existing instructions.
However, such a thing as "impossibility" only deters scientists, not engineers :-)...
What I have been thinking is this: In nature, real mutations work a lot more like LLVM-mutate that like what we do in normal Genetic Programming. In other words, they simply swap letters out of a very limited set (A,T,C,G) and every possible variation comes out of this. We could have a program or set of programs with an initial set of instructions, plus a set of "possible functions" either linked or defined in the program. Most of these functions would not be actually used, but they will be there to provide "raw DNA" for mutations, just like in our DNA. This set of functions would have the complete (or semi-complete) set of possible functions for a problem space. Then, we simply use basic operations like the ones in LLVM-mutate.
Some possible problems though:
Given the amount of possible variability, the only way to have
acceptable execution times would be to have massive amounts of
computing power. Possibly achievable in the Cloud or with GPUs.
You would still have to contend with Mr. Turing's Halting Problem.
However I think this could be resolved by running the solutions in a
"Sandbox" that doesn't take you down if the solution blows up:
Something like a single-use virtual machine or a Docker-like
container, with a time limitation (to get out of infinite loops). A
solution that crashes or times out would get the worst possible
fitness, so that the programs would tend to diverge away from those
paths.
As to why do this at all, I can see a number of interesting applications: Self-healing programs, programs that self-optimize for an specific environment, program "vaccination" against vulnerabilities, mutating viruses, quality assurance, etc.
I think there's a potential open source project here. It would be insane, dangerous and a time-sucking vortex: Just my kind of project. Count me in if someone doing it.
I've been trying to make use of the GPU as part of a project of mine. I've looked into both CUDA and OpenCL, but the lack of information showing you how to introduce these into a project is shocking. Even their dedicated forum groups are dead. So now, I'm looking into DirectCompute.
From what I can tell, it's simply a new type of shader file that makes use of HLSL. My question is this, does my program (aside from being DirectX 10 / 11 ) need its structure changed?
I mean, is it simply a case of creating the CS file, setting in the project like I would any other shader, and watch the magic happen?
Any information on this would be appreciated.
Yes CS fits into the usual DirectX programming structure. It works in a similar way to CUDA/OpenCL. Here is a good, simple example:
http://openvidia.sourceforge.net/index.php/DirectCompute
Personally I would suggest using CUDA/OpenCL rather than going the DirectCompute route if your project does not involve graphics. I think CUDA/OpenCL are better for general-purpose computing. It can be a little difficult to find documentation but these are the main aspects to GPU programming:
Setting up data on the CPU to pass to the GPU.
Understanding how many warps/threads need to be started on the GPU, how threads might need to communicate, etc.
Computing on the GPU, reading data back on the CPU
Another option is C++ AMP - please follow links from here for more info and feel free to post questions as you have them: http://blogs.msdn.com/b/nativeconcurrency/archive/2011/09/13/c-amp-in-a-nutshell.aspx
Easiest way - is to make project which uses CS with C# and SlimDX.
And here is good site with basics how to use CS from within C# code.
Later on you can move to full scale CS exploration with C++ and DirectX 11.
Let's say that you have to implement some functionality that is not trivial (it will take at least 1 work week). You have a SDK/API/library that contains (numerous) code samples demonstrating the usage of the part of the SDK for implementing that functionality.
How do you approach learning all the samples, extract the necessary information, techniques, etc. in order to use them to implement the 'real thing'. The key questions are:
Do you use some tool for diagramming of the control flow, the interactions between the functions from the SDK, and the sample itself? Which kind of diagrams do you find useful? (I was thinking that the UML sequence diagram can be quite useful together with the debugger in this case).
How do you keep the relevant and often interrelated information about SDK/API function calls, the general structure and calls order in the sample programs that have to be used as a reference - mind maps, some plain text notes, added comments in the samples code, some refactoring of the sample code to suit your personal coding style in order to make the learning easier?
Personally I use the prototyping approach. Keep development to manageable iterations. In the beginning, those iterations are really small. As part of this, don't be afraid to throw code away and start again (everytime I say that somewhere a project manager has a heart attack).
If your particular task can't easily or reasonably be divided into really small starting tasks then start with some substitute until you get going.
You want to keep it as simple as you can (the proverbial "Hello world") just to familiarize yourself with building, deploying, debugging, what error messages look like, the simple things that can and do go wrong in the beginning, etc.
I don't go as far as using a diagramming tool sorry (I barely see the point in that for my job).
As soon as you start trying things you'll get the hang of it, even if in the beginning you have no idea of what's going on and why what you're doing works (or doesn't).
I usually compile and modify the examples, making them fit something that I need to do myself. I tend to do this while using and annotating the corresponding documents. Being a bit old school, the tool I usually use for diagramming is a pencil, or for the really complex stuff two or more colored pens.
I am by no means a seasoned programmer. In fact, I am learning C++ and I've been studying the language primarily from books. When I try to stray from the books (which happens a lot because I want to start contributing to programs like LibreOffice), for example, I find myself being lost. Furthermore, when I'm using functionality of the library, my implementations are wrong because I don't really understand how the library was created and/or why things need to be done that way. When I look at sample source code, I see how something is done, but I don't understand why it's done that way which leads to poor design of my programs. And as a result, I'm constantly guessing at how to do something and dealing with errors as I encounter them. Very unproductive and frustrating.
Going back to my book comment, two books which I have ready from cover to cover more than once are Ivor Horton's Beginning Visual C++ 2010 and Starting Out with C++: Early Objects (7th Edition). What I really loved about Ivor Horton's book is that it contained thorough explanation of why something needs to be done a certain way. For example, before any Windows programming began, lots of explanation about how Windows works was given first. Understanding how and why things work a certain way really helps in how I develop software.
So to contribute my two pennies towards answering your question. I think the best approach is to pick up well written books and sit down and begin learning about that library, API, SDK, whatever in a structured approach that offers real-world examples along with explanations as to how and why things are implemented as they are.
I don't know if I totally missed your question, but I don't think I did.
Cheers!
This was my first post on this site. Don't rip me too hard. (:
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I'm preparing to teach someone to program. When I learned the course material, I used turtle graphics for the first few exercises. In reading introductory textbooks, I have not found one that uses the technique. Did others find this approach helpful? If not, what is a better way to learn to program?
I think it depends on age of the target group.
If they are children (I would say up to 12-14 years), doing any easy graphics is a good way to motivate them; on the other hand, don't expect them to learn much about real programming or algorithms.
If they are teens (14-18), it's perhaps still good to use some algorithms that give pretty results (for example 3D or fractals), but since they are older and capable of more abstract thinking, I don't think 2D turtle graphics is interesting enough.
If they are older, doing any graphics is a distraction. At that age, they should have enough inner motivation to learn without anything fancy.
To sum up, I think that fancy graphics serves more motivational role (that you see what you did fast, and it's easy to show others what can you do with a computer) than learning role (that it would make learning real programming easier).
In the late 80s, before I was programming in C, I was programming in Applesoft BASIC and Logo. As a child I thought the turtle was great because it make programming simple. If I decide to teach my children Logo I will probably start here to get an actively developed Logo interpreter.
The key thing about LOGO is user-defined functions. It is very good at conveying that, as long as you emphasize it. Show interactively how to draw a square, then make a new word called square. Then show how you can draw patterns using square. Then make those patterns into words, and so on.
You could do worse in teaching programming than using a tool like Scratch. It's a drag and drop programming interface and can be used to teach basic concepts of programming with some fun visual results (as can be seen from the gallery on their website).
Rob
Logo gave me a very clear picture (no pun intended) on how recursive functions would work, and since I was doing assembly programming at the time, the need to return to the previous state when returning to a method became very clear with Logo.
Recursive implementations of things where also very easy to see the effect of.
I wrote script/code in a c-like dialect for a game called Doom2 before I knew what programming was, so when it came to seriously learning about concepts such as pointers, inheritance and polymorphism I found the basics a breeze because I could construct a mental model to not only help me understand, but also appreciate how cool things like pointers and arrays are.
A friend of mine is a good programming student, but he gets frustrated when he can't visualize an algorithm working, when I was starting to help other students I found they had the same problem, if they can't see something working it's harder to appreciate as a fledgling programmer, the same friend eloquently suggested I "Show 'em some crazy pimp shit and then show them how it's done". He's right, even if someone really wants to learn something they'll be able to draw on more mental energy if they think what they're learning lets them do awesome things.
My best bit of advice is this: AT THE START SPEND AS LITTLE TIME PROGRAMMING TO THE CONSOLE AS POSSIBLE
It makes you feel constrained and your efforts appear futile, only after you appreciate it as a front end should it be used for learning to program. I wouldn't use logo myself because I don't think it can teach concepts such as the aforementioned polymorphism or inheritance nearly as well as other methods, I know a friend of mine is teaching a teenager how to program using XNA in a wrapper, I think anything that can let you blit an image to the screen is fine. That way you can see why you'd want an abstract base class called EnemyEntity with behavior that's inherited by zombie and dog etc. It's not that the concepts are hard to understand, it's just that at first they're hard to appreciate.
I could go on but I think that puts across what I've learned by teaching others. I think using graphics in teaching programming allows students to gain the ability to build mental models of intangible concepts faster than any other.
XNA If you want to teach C# that's an amazing graphics library, just write a wrapper sprite class to hide as much complexity when first starting out and teaching concepts.
SDL A lower level library if you're going to start with c++
During one of my first-year computer science papers we used Java to create fractal patterns via a turtle object.
It was pretty fun to see visually whether or not we had correctly implemented the algorithm required to produce a certain pattern. However, so answer the main question, I wouldn't say that programming via a turtle is useful. I'd say the best way to teach someone to program is to get them to build their own app to do whatever they want it to do. This gives them creative control, plus if they get stuck they can learn how to resolve a problem.
I strongly suggest to start with a interpreted language like Logo (not compiled) because of the quality of the error messages. Reading error messages is very important in this process. Also, at the easy level, Logo allows you to run your instructions one by one in direct mode and carry them to your procedures when you get the expected results.
# Alex: MicroWorlds is a commercial version of Logo and it does exist in English, Spanish, Portuguese, Italian, Russian, etc. it's a big plus if you are not a native English-speaking person.
LOGO is not only Turtle-Graphics.
There are also other interesting concepts in it which come from LISP.
'Turtle' is just icing on the cake and the "imperative" side of Logo.
:)
I learned to program in BASIC by writing simple programs drawing faces (I mean circles and squares) on the screen. Somehow the whole turtle programming was never my thing, although a few of my friends learned that way. Later on I moved to Pascal, then to Delphi, Java and C++/C#.
In my opinion the trick is to "wow" your student and impress/empower with potential things that you can accomplish by writing your own programs. I would actually demonstrate some GUI programming or game programming. It's much easier to learn the basics by keeping the end goal in mind.
Recently I came across SmallBasic - a cool programming environment for kids designed to teach concepts. I would give that a try. It comes with a pretty complete paper describing how to use it.
When I got my first computer (VIC-20) and started programming it was very hard to explain to my parents what I was doing.
My mother tok a course in computing preparing for a project of computerizing the library she worked in. They had a couple of classes introducing them to programming. After learning LOGO she came home and said that she suddenly understood what I was into.
So LOGO with turtle graphics brought us closer together!
I did a "computing for kids" course in the late eighties, and there was an extensive section on turtle graphics using logo. In all honesty I was bored to tears, and learned virtually nothing from it.
I think "programming the turtle" might work better for someone who is artistically inclined, or hugely into geometry, but by and large, there are far more interesting problems to attack, even for kids.
Ah, the memories of good old Logo. I think I got more of a geometry lesson than a programming lesson out of it, e.g. figuring out how much to turn at various points to produce a particular shape, design or pattern. It may work if you plan on mixing geometry with the programming, but if the person doesn't have the basics of geometry, e.g. what is a square and how is it different from other 4-sided shapes, what is a triangle, etc.
I used logo and turtle at school too, a great introduction.
It looks like our kids will be getting a slightly updated interface with Microsoft Kodu. It looks very impressive. It's an icon based programming language made for creating games that runs on X-Box Live.
I'm currently learning python and using a little bit of turtle. In labs we haven't used it, but our homework does. It's nice to know it exists, and it's a good way to get certain commands and syntax in. Overall I don't feel it was completely necessary though.
When I was young, I found it very interesting. It was one of the first programming languages that I've learned, even though I've used it for about two days. It started my interest in programming.
Nowadays, I think the syntax is a bit unclear because most statements are abbreviations. Nowadays, computers are far more powerful thus the language could profit from clearer statement. Another factor is the native language of the person who is learning to use it. If English is not your native language then Logo becomes a bit more complex to understand. So if you're teaching Logo to children, make sure they're familiar with English terms first. (Quite easy if you're a native English-speaking person. More complex if you're originally Dutch, German, French, Portuguese. Even more complex if you're Russian or Chinese because you'd have to adjust to a different character set too.)
I have just begun teaching my 7-year-old how to program using Logo, and he is having a load of fun with it. The commands are easy enough for his limited reading ability and he just loves drawing cool pictures using the turtle graphics. I was amazed at how well he retained what he had learned using it, so I feel it was a good choice for his age.
For older kids (or adults) other languages might have more advantages as a beginner language though
Personal experience, YMMV...
My first encounter with a computer was turtle graphics in my early teens. I loved and was immediately hooked. (Perhaps because for the first time someone [something] did exactly what I told it to do?)
The visual and instant feedback made me want to do more and more. I really wanted to figure out how to replicate the pictures I saw in the book I was using. Without me even classifying it as "work", it slowly built up my early programming skills and my confidence I could learn on my own.
I credit it with sending me in the path I'm in today, a happy software developer who can't believe I get paid to do this work (I know, I know - all corporate snickering aside, I like my work).
As I said, YMMV.