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• IPv6, isn't it just a few extra bits?

  - by rclewis

  It's always an interesting task, to try and explain what you do to family and friends. I have described IPv6 as the "Next Generation Internet"  or "Second Internet" but the hollow expressions on my kids faces scream for the instant relief of the latest video game.  Never one to give up easily, I have formulated a new example - the Post Office... Similar to the Post Office the Internet delivers mail and packages based on addresses. As the number of residences, businesses, and delivery locations increased, the 5 digit ZIP Code (Washington, DC 20005) was expanded to ZIP+4  allowing for more precise delivery points (Postmaster General, Washington, DC 20260-3100). Ah, if only computers were as simple.  IPv6 isn't an add-on or expansion of the existing IPv4 Addressing, it is a new addressing model which will allow the internet to grow from a single computer in the basement of a university or your parents kitchen table, to support the multitude of smart phones, smart TV's, tablets, dvr's, and disk players, all clambering to connect for information. Unfortunetly there are only a finite number of IPv4 public addresses left, and those are being consumed at an ever increasing rate. Few people could have predicted the explosive growth of the internet or the shortage of IPv4 addresses we now face - but there is a "Plan B" and that is the vastly larger address space of IPv6.  Many in the industry have labeled this a "business continuity" problem,  when in fact most companies will be able to continue conducting business once they run out of existing IPv4 Addresses. The problem is really a Customer Continuity problem, how will businesses communicate with existing customers and reach new customers online who's only option is to adopt IPv6 when IPv4 is depleted? Perhaps a first step is publishing a blog that is also accessible via IPv6, it's just a few extra bits. Join us for the Oracle OpenWorld 2012 Session:   Navigating IPv6 @ Oracle Thursday, Oct. 4th 2:15PM - 3:15PM  Palace Hotel - Concert   Learn more about IPv6 Technologies at Oracle

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• Using game of life or other virtual environment for artificial (intelligence) life simulation? [clos

  - by Berlin Brown

  One of my interests in AI focuses not so much on data but more on biologic computing. This includes neural networks, mapping the brain, cellular-automata, virtual life and environments. Described below is an exciting project that includes develop a virtual environment for bots to evolve in. "Polyworld is a cross-platform (Linux, Mac OS X) program written by Larry Yaeger to evolve Artificial Intelligence through natural selection and evolutionary algorithms." http://en.wikipedia.org/wiki/Polyworld " Polyworld is a promising project for studying virtual life but it still is far from creating an "intelligent autonomous" agent. Here is my question, in theory, what parameters would you use create an AI environment? Possibly a brain environment? Possibly multiple self contained life organisms that have their own "brain" or life structures. I would like a create a spin on the game of life simulation. What if you have a 64x64 game of life grid. But instead of one grid, you might have N number of grids. The N number of grids are your "life force" If all of the game of life entities die in a particular grid then that entire grid dies. A group of "grids" makes up a life form. I don't have an immediate goal. First, I want to simulate an environment and visualize what is going on in the environment with OpenGL and see if there are any interesting properties to the environment. I then want to add "scarce resources" and see if the AI environment can manage resources adequately.

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• Objective-measures of the expressiveness of programming languages [closed]

  - by Casebash

  I am very interested in the expressiveness of different languages. Everyone who has programmed in multiple languages knows that sometimes a language allows you to express concepts which you can't express in other languages. You can have all kinds of subjective discussion about this, but naturally it would be better to have an objective measure. There do actually exist objective measures. One is Turing-Completeness, which means that a language is capable of generating any output that could be generated by following a sequential set of steps. There are also other lesser levels of expressiveness such as Finite State Automata. Now, except for domain specific languages, pretty much all modern languages are Turing complete. It is therefore natural to ask the following question: Can we can define any other formal measures of expressiveness which are greater than Turing completeness? Now of course we can't define this by considering the output that a program can generate, as Turing machines can already produce the same output that any other program can. But there are definitely different levels in what concepts can be expressed - surely no-one would argue that assembly language is as powerful as a modern object oriented language like Python. You could use your assembly to write a Python interpreter, so clearly any accurate objective measure would have to exclude this possibility. This also causes a problem with trying to define the expressiveness using the minimum number of symbols. How exactly to do so is not clear and indeed appears extremely difficult, but we can't assume that just because we don't know how to solve a problem, that nobody know how to. It is also doesn't really make sense to demand a definition of expressiveness before answering the question - after all the whole point of this question is to obtain such a definition. I think that my explanation will be clear enough for anyone with a strong theoretical background in computer science to understand what I am looking for. If you do have such a background and you disagree, please comment why, but if you don't thats probably why you don't understand the question.

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• snort analysis of wireshark capture

  - by Ben Voigt

  I'm trying to identify trouble users on our network. ntop identifies high traffic and high connection users, but malware doesn't always need high bandwidth to really mess things up. So I am trying to do offline analysis with snort (don't want to burden the router with inline analysis of 20 Mbps traffic). Apparently snort provides a -r option for this purpose, but I can't get the analysis to run. The analysis system is gentoo, amd64, in case that makes any difference. I've already used oinkmaster to download the latest IDS signatures. But when I try to run snort, I keep getting the following error: % snort -V ,,_ -*> Snort! <*- o" )~ Version 2.9.0.3 IPv6 GRE (Build 98) x86_64-linux '''' By Martin Roesch & The Snort Team: http://www.snort.org/snort/snort-team Copyright (C) 1998-2010 Sourcefire, Inc., et al. Using libpcap version 1.1.1 Using PCRE version: 8.11 2010-12-10 Using ZLIB version: 1.2.5 %> snort -v -r jan21-for-snort.cap -c /etc/snort/snort.conf -l ~/snortlog/ (snip) 273 out of 1024 flowbits in use. [ Port Based Pattern Matching Memory ] +- [ Aho-Corasick Summary ] ------------------------------------- | Storage Format : Full-Q | Finite Automaton : DFA | Alphabet Size : 256 Chars | Sizeof State : Variable (1,2,4 bytes) | Instances : 314 | 1 byte states : 304 | 2 byte states : 10 | 4 byte states : 0 | Characters : 69371 | States : 58631 | Transitions : 3471623 | State Density : 23.1% | Patterns : 3020 | Match States : 2934 | Memory (MB) : 29.66 | Patterns : 0.36 | Match Lists : 0.77 | DFA | 1 byte states : 1.37 | 2 byte states : 26.59 | 4 byte states : 0.00 +---------------------------------------------------------------- [ Number of patterns truncated to 20 bytes: 563 ] ERROR: Can't find pcap DAQ! Fatal Error, Quitting.. net-libs/daq is installed, but I don't even want to capture traffic, I just want to process the capture file. What configuration options should I be setting/unsetting in order to do offline analysis instead of real-time capture?

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• A star vs internet routing pathfinding

  - by alan2here

  In many respects pathfinding algorythms like A star for finding the shortest route though graphs are similar to the pathfinding on the internet when routing trafic. However the pathfinding routers perform seem to have remarkable properties. As I understand it: It's very perfromant. New nodes can be added at any time that use a free address from a finite (not tree like) address space. It's real routing, like A*, theres never any doubling back for example. IP addresses don't have to be geographicly nearby. The network reacts quickly to changes to the networks shape, for example if a line is down. Routers share information and it takes time for new IP's to be registered everywhere, but presumably every router dosn't have to store a list of all the addresses each of it's directions leads most directly to. I can't find this information elsewhere however I don't know where to look or what search tearms to use. I'm looking for a basic, general, high level description to the algorithms workings, from the point of view of an individual router.

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• How to Log Into a Web App Simultaneously with Different Account?

  - by Ngu Soon Hui

  I want to log into a web application, using at least ten account names at one single point of time ( I am not trying to do anything illegal, so don't worry). AFAIK, each tab in Chrome will share the same session, therefore, for one machine, one can use Google Chrome to log in at most 2 accounts, one in normal mode, another in Incognito mode. Is there anyway I can log into multiple accounts? I know I can open up IE and Firefox ( probably Safari etc) and login, but this is not really scalable as the number of web browsers is finite. Edit: My application is a localhost application; it resides on my computer. So proxy may not be that useful, and you now probably understand why it's nothing illegal. Edit2: CookieSwap seems like a good idea, but the problem is that once I swap the cookie, all the tabs and the FF apps' cookie are swap as well. Can the swapping be done on a tab basis or on application basis, so that on a dual-monitor, I can see the different login side-by-side?

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• Customer Spotlight - CSX: Charles Pack

  - by cwarticki

  A couple of weeks ago, I had the distinct privilege of facilitating a training session with CSX.  CSX is a wonderful customer.  They've been a dedicated Oracle customer for many years. They have quite an extensive Oracle footprint including Server Technologies, Fusion Middleware and E-Business Suite products.  They also utilize Oracle's Solution Support Center offering from Advanced Customer Services, for their Database products. I'm always on the lookout for Oracle gems and I discovered one at CSX. Before my session began, I met with Charles Pack.  In my view, he's an Oracle guru.  Don't take my word for it, just read any of the books he's authored or co-authored and the one soon to be released.  Just looking at his bookshelf, I saw titles going back to Oracle 7 & 8, as well as a Solaris 2.x book.  Remember those?   Anyway, Charles is a technologist and a manager (and wears numerous other hats too).  I had a wonderful time talking with Charles and getting to know him.  What do you consider keys to your personal success?  Inability to quit.  When I decide that I will accomplish something, I will, regardless of the nature of the challenge.  Never quitting means a perpetual drive for change and progress and setting examples for others to follow.  The reason I write OCP books is because I can provide a path for people to improve their knowledge of the product, gain a certification, and reach their professional goals. What do you consider the most important part of your job?  Negotiations.  We all have competing goals, incentives and finite resources, but we should all have the same common goal – progress.  So finding the way for all parties to progress is the most important thing we do. What is the most important part of your relationship with Oracle?  Oracle provides solutions – not just products - that are critical to our business success.  So continuous communication regarding education, services, product roadmaps and shared goals is the most important part of our ongoing relationship. Charles is an Oracle loyalist.  His career has been based on using our products and he's passionate about the products he works with.  You can tell, just by talking with him.  I appreciate Charles and other customers like him.  He's an expert in his field and an Oracle evangelist.  He is an asset to CSX and to their success.  He's an advocate for Oracle and an asset to our customers.  You can also friend and follow Charles on Twitter @charlesapack It was a pleasure meeting you Charles! -Chris Warticki Global Customer Management

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• Drawing random smooth lines contained in a square [migrated]

  - by Doug Mercer

  I'm trying to write a matlab function that creates random, smooth trajectories in a square of finite side length. Here is my current attempt at such a procedure: function [] = drawroutes( SideLength, v, t) %DRAWROUTES Summary of this function goes here % Detailed explanation goes here %Some parameters intended to help help keep the particles in the box RandAccel=.01; ConservAccel=0; speedlimit=.1; G=10^(-8); % %Initialize Matrices Ax=zeros(v,10*t); Ay=Ax; vx=Ax; vy=Ax; x=Ax; y=Ax; sx=zeros(v,1); sy=zeros(v,1); % %Define initial position in square x(:,1)=SideLength*.15*ones(v,1)+(SideLength*.7)*rand(v,1); y(:,1)=SideLength*.15*ones(v,1)+(SideLength*.7)*rand(v,1); % for i=2:10*t %Measure minimum particle distance component wise from boundary %for each vehicle BorderGravX=[abs(SideLength*ones(v,1)-x(:,i-1)),abs(x(:,i-1))]'; BorderGravY=[abs(SideLength*ones(v,1)-y(:,i-1)),abs(y(:,i-1))]'; rx=min(BorderGravX)'; ry=min(BorderGravY)'; % %Set the sign of the repulsive force for k=1:v if x(k,i)<.5*SideLength sx(k)=1; else sx(k)=-1; end if y(k,i)<.5*SideLength sy(k)=1; else sy(k)=-1; end end % %Calculate Acceleration w/ random "nudge" and repulive force Ax(:,i)=ConservAccel*Ax(:,i-1)+RandAccel*(rand(v,1)-.5*ones(v,1))+sx*G./rx.^2; Ay(:,i)=ConservAccel*Ay(:,i-1)+RandAccel*(rand(v,1)-.5*ones(v,1))+sy*G./ry.^2; % %Ad hoc method of trying to slow down particles from jumping outside of %feasible region for h=1:v if abs(vx(h,i-1)+Ax(h,i))<speedlimit vx(h,i)=vx(h,i-1)+Ax(h,i); elseif (vx(h,i-1)+Ax(h,i))<-speedlimit vx(h,i)=-speedlimit; else vx(h,i)=speedlimit; end end for h=1:v if abs(vy(h,i-1)+Ay(h,i))<speedlimit vy(h,i)=vy(h,i-1)+Ay(h,i); elseif (vy(h,i-1)+Ay(h,i))<-speedlimit vy(h,i)=-speedlimit; else vy(h,i)=speedlimit; end end % %Update position x(:,i)=x(:,i-1)+(vx(:,i-1)+vx(:,i))/2; y(:,i)=y(:,i-1)+(vy(:,i-1)+vy(:,1))/2; % end %Plot position clf; hold on; axis([-100,SideLength+100,-100,SideLength+100]); cc=hsv(v); for j=1:v plot(x(j,1),y(j,1),'ko') plot(x(j,:),y(j,:),'color',cc(j,:)) end hold off; % end My original plan was to place particles within a square, and move them around by allowing their acceleration in the x and y direction to be governed by a uniformly distributed random variable. To keep the particles within the square, I tried to create a repulsive force that would push the particles away from the boundaries of the square. In practice, the particles tend to leave the desired "feasible" region after a relatively small number of time steps (say, 1000)." I'd love to hear your suggestions on either modifying my existing code or considering the problem from another perspective. When reading the code, please don't feel the need to get hung up on any of the ad hoc parameters at the very beginning of the script. They seem to help, but I don't believe any beside the "G" constant should truly be necessary to make this system work. Here is an example of the current output: Many of the vehicles have found their way outside of the desired square region, [0,400] X [0,400].

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• Is there a perfect algorithm for chess?

  - by Overflown

  Dear Stack Overflow community, I was recently in a discussion with a non-coder person on the possibilities of chess computers. I'm not well versed in theory, but think I know enough. I argued that there could not exist a deterministic Turing machine that always won or stalemated at chess. I think that, even if you search the entire space of all combinations of player1/2 moves, the single move that the computer decides upon at each step is based on a heuristic. Being based on a heuristic, it does not necessarily beat ALL of the moves that the opponent could do. My friend thought, to the contrary, that a computer would always win or tie if it never made a "mistake" move (however do you define that?). However, being a programmer who has taken CS, I know that even your good choices - given a wise opponent - can force you to make "mistake" moves in the end. Even if you know everything, your next move is greedy in matching a heuristic. Most chess computers try to match a possible end game to the game in progress, which is essentially a dynamic programming traceback. Again, the endgame in question is avoidable though. -- thanks, Allan Edit: Hmm... looks like I ruffled some feathers here. That's good. Thinking about it again, it seems like there is no theoretical problem with solving a finite game like chess. I would argue that chess is a bit more complicated than checkers in that a win is not necessarily by numerical exhaustion of pieces, but by a mate. My original assertion is probably wrong, but then again I think I've pointed out something that is not yet satisfactorily proven (formally). I guess my thought experiment was that whenever a branch in the tree is taken, then the algorithm (or memorized paths) must find a path to a mate (without getting mated) for any possible branch on the opponent moves. After the discussion, I will buy that given more memory than we can possibly dream of, all these paths could be found.

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• What is private bytes, virtual bytes, working set?

  - by Devil Jin

  I am using perfmon windows utility to debug memory leak in a process. Perfmon explaination: Working Set- Working Set is the current size, in bytes, of the Working Set of this process. The Working Set is the set of memory pages touched recently by the threads in the process. If free memory in the computer is above a threshold, pages are left in the Working Set of a process even if they are not in use. When free memory falls below a threshold, pages are trimmed from Working Sets. If they are needed they will then be soft-faulted back into the Working Set before leaving main memory. Virtual Bytes- Virtual Bytes is the current size, in bytes, of the virtual address space the process is using. Use of virtual address space does not necessarily imply corresponding use of either disk or main memory pages. Virtual space is finite, and the process can limit its ability to load libraries. Private Bytes- Private Bytes is the current size, in bytes, of memory that this process has allocated that cannot be shared with other processes. Q1. Is it the private byte should I measure to be sure if the process is having any leak as it does not involve any shared libraries and any leak if happening will be coming from the process itself? Q2. What is the total memory consumed by the process? Is it the Virtual byte size? or Is it the sum of Virtual Bytes and Working Set Q3. Is there any relation between private bytes, working set and virtual bytes. Q4. Any tool which gives a better idea memory information?

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• SQL select descendants of a row

  - by Joey Adams

  Suppose a tree structure is implemented in SQL like this: CREATE TABLE nodes ( id INTEGER PRIMARY KEY, parent INTEGER -- references nodes(id) ); Although cycles can be created in this representation, let's assume we never let that happen. The table will only store a collection of roots (records where parent is null) and their descendants. The goal is to, given an id of a node on the table, find all nodes that are descendants of it. A is a descendant of B if either A's parent is B or A's parent is a descendant of B. Note the recursive definition. Here is some sample data: INSERT INTO nodes VALUES (1, NULL); INSERT INTO nodes VALUES (2, 1); INSERT INTO nodes VALUES (3, 2); INSERT INTO nodes VALUES (4, 3); INSERT INTO nodes VALUES (5, 3); INSERT INTO nodes VALUES (6, 2); which represents: 1 `-- 2 |-- 3 | |-- 4 | `-- 5 | `-- 6 We can select the (immediate) children of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1; We can select the children and grandchildren of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1 UNION ALL SELECT b.* FROM nodes AS a, nodes AS b WHERE a.parent=1 AND b.parent=a.id; We can select the children, grandchildren, and great grandchildren of 1 by doing this: SELECT a.* FROM nodes AS a WHERE parent=1 UNION ALL SELECT b.* FROM nodes AS a, nodes AS b WHERE a.parent=1 AND b.parent=a.id UNION ALL SELECT c.* FROM nodes AS a, nodes AS b, nodes AS c WHERE a.parent=1 AND b.parent=a.id AND c.parent=b.id; How can a query be constructed that gets all descendants of node 1 rather than those at a finite depth? It seems like I would need to create a recursive query or something. I'd like to know if such a query would be possible using SQLite. However, if this type of query requires features not available in SQLite, I'm curious to know if it can be done in other SQL databases.

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• Workflow engine BPMN, Drools, etc or ESB?

  - by Tom

  We currently have an application that is based on an in-house developed workflow engine with YAML based DSL. We are looking to move parts of it to Java. I have discovered a number of java solutions like Intalio, JBPM, Drools Expert, Drools Flow etc. They appear to be aimed at businesses where the business analyst creates the workflows using a graphical editor and submits them to the workflow engine. They seem geared towards ease of use for non-technical people rather than for developers with a focus on human interaction. The workflows tend to look like. Discover-a-file -\ -> join -> process-file -> move-file -> register-file Discover-some-metadata -/ If any step fails we need to retry it X times. We also need to be able to stop the system and be able to restart it and have it continue from where it was (durable). Some of our workflows can be defined by a set of goals we need to achieve so Jess's backwards rule chaining sounds interesting but it is not open source. It might be that what we are after is a Finite State Machine engine or just an Enterprise Service Bus and do everything as JMS queues. Is there a good open source workflow engine that is both standards-based but also geared towards developers. We don't particular want to use a graphical workflow designer or write reams of XML and it should ideally be in Java or language agnostic (makes REST/Soap calls to external services). Thanks, Tom

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• Haskell Linear Algebra Matrix Library for Arbitrary Element Types

  - by Johannes Weiß

  I'm looking for a Haskell linear algebra library that has the following features: Matrix multiplication Matrix addition Matrix transposition Rank calculation Matrix inversion is a plus and has the following properties: arbitrary element (scalar) types (in particular element types that are not Storable instances). My elements are an instance of Num, additionally the multiplicative inverse can be calculated. The elements mathematically form a finite field (??2256). That should be enough to implement the features mentioned above. arbitrary matrix sizes (I'll probably need something like 100x100, but the matrix sizes will depend on the user's input so it should not be limited by anything else but the memory or the computational power available) as fast as possible, but I'm aware that a library for arbitrary elements will probably not perform like a C/Fortran library that does the work (interfaced via FFI) because of the indirection of arbitrary (non Int, Double or similar) types. At least one pointer gets dereferenced when an element is touched (written in Haskell, this is not a real requirement for me, but since my elements are no Storable instances the library has to be written in Haskell) I already tried very hard and evaluated everything that looked promising (most of the libraries on Hackage directly state that they wont work for me). In particular I wrote test code using: hmatrix, assumes Storable elements Vec, but the documentation states: Low Dimension : Although the dimensionality is limited only by what GHC will handle, the library is meant for 2,3 and 4 dimensions. For general linear algebra, check out the excellent hmatrix library and blas bindings I looked into the code and the documentation of many more libraries but nothing seems to suit my needs :-(. Update Since there seems to be nothing, I started a project on GitHub which aims to develop such a library. The current state is very minimalistic, not optimized for speed at all and only the most basic functions have tests and therefore should work. But should you be interested in using or helping out developing it: Contact me (you'll find my mail address on my web site) or send pull requests.

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• Backreferences in lookbehind

  - by polygenelubricants

  Can you use backreferences in a lookbehind? Let's say I want to split wherever behind me a character is repeated twice. String REGEX1 = "(?<=(.)\\1)"; // DOESN'T WORK! String REGEX2 = "(?<=(?=(.)\\1)..)"; // WORKS! System.out.println(java.util.Arrays.toString( "Bazooka killed the poor aardvark (yummy!)" .split(REGEX2) )); // prints "[Bazoo, ka kill, ed the poo, r aa, rdvark (yumm, y!)]" Using REGEX2 (where the backreference is in a lookahead nested inside a lookbehind) works, but REGEX1 gives this error at run-time: Look-behind group does not have an obvious maximum length near index 8 (?<=(.)\1) ^ This sort of make sense, I suppose, because in general the backreference can capture a string of any length (if the regex compiler is a bit smarter, though, it could determine that \1 is (.) in this case, and therefore has a finite length). So is there a way to use a backreference in a lookbehind? And if there isn't, can you always work around it using this nested lookahead? Are there other commonly-used techniques?

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• Change Data Capture or Change Tracking - Same as Traditional Audit Trail Table?

  - by HardCode

  Before I delve into the abyss of Microsoft documentation any deeper, I'd like to know if someone experienced with Change Data Capture and Change Tracking know if one or both of these can be used to replace the traditional ... "Audit trail table copy of the 'real table' (all of the fields of the original table, plus date/time, user ID, and DML action field) inserted into by Triggers" ... setup for a database table audit trail, where the trigger populates the audit trail table (which is all manual work). The MSDN overview documentation explains at a high level what Change Data Capture and Change Tracking are, but it isn't clear enough to me, and doesn't state outright, that these tools can be used to replace the traditional audit trail tables we've made so often. Can someone with any experience using Change Data Capture and Change Tracking save me a lot of time, or confirm that I am spending time looking at the right tool? The critical part of our audit trail is capturing all changes to a table's fields (on INSERT, UPDATE, DELETE), when it happened, and who did it. These changes are commonly provided to an end user chronologically via an audit trail report. Which is another question ... Change Data Capture or Change Tracking is the solution, I'd assume that this data can be queried just like data from a normal table? EDIT: I need a permanent audit trail, irregardless of time. I see that Change Data Capture has to do with the transaction logs, so this sounds finite to me.

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• Examples of monoids/semigroups in programming

  - by jkff

  It is well-known that monoids are stunningly ubiquitous in programing. They are so ubiquitous and so useful that I, as a 'hobby project', am working on a system that is completely based on their properties (distributed data aggregation). To make the system useful I need useful monoids :) I already know of these: Numeric or matrix sum Numeric or matrix product Minimum or maximum under a total order with a top or bottom element (more generally, join or meet in a bounded lattice, or even more generally, product or coproduct in a category) Set union Map union where conflicting values are joined using a monoid Intersection of subsets of a finite set (or just set intersection if we speak about semigroups) Intersection of maps with a bounded key domain (same here) Merge of sorted sequences, perhaps with joining key-equal values in a different monoid/semigroup Bounded merge of sorted lists (same as above, but we take the top N of the result) Cartesian product of two monoids or semigroups List concatenation Endomorphism composition. Now, let us define a quasi-property of an operation as a property that holds up to an equivalence relation. For example, list concatenation is quasi-commutative if we consider lists of equal length or with identical contents up to permutation to be equivalent. Here are some quasi-monoids and quasi-commutative monoids and semigroups: Any (a+b = a or b, if we consider all elements of the carrier set to be equivalent) Any satisfying predicate (a+b = the one of a and b that is non-null and satisfies some predicate P, if none does then null; if we consider all elements satisfying P equivalent) Bounded mixture of random samples (xs+ys = a random sample of size N from the concatenation of xs and ys; if we consider any two samples with the same distribution as the whole dataset to be equivalent) Bounded mixture of weighted random samples Which others do exist?

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• BackgroundWorker might be causing my application to hang

  - by alexD

  I have a Form that uses a BackgroundWorker to execute a series of tests. I use the ProgressChanged event to send messages to the main thread, which then does all of the updates on the UI. I've combed through my code to make sure I'm not doing anything to the UI in the background worker. There are no while loops in my code and the BackgroundWorker has a finite execution time (measured in seconds or minutes). However, for some reason when I lock my computer, often times the application will be hung when I log back in. The thing is, the BackgroundWorker isn't even running when this happens. The reason I believe it is related to the BackgroundWorker though is because the form only hangs when the BackgroundWorker has been executed since the application was loaded (it only runs when given a certain user input). I pass this thread a List of TreeNodes from a TreeView in my UI through the RunWorkerAsync method, but I only read those nodes in the worker thread..any modifications I make to them is done in the UI thread through the progressChanged event. I do use Thread.Sleep in my worker thread to execute tests at timed intervals (which involves sending messages over a TCP socket, which was not created in the worker thread). I am completely perplexed as to why my application might be hanging. I'm sure I'm doing something 'illegal' somewhere, I just don't know what.

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• Creating a smart text generator

  - by royrules22

  I'm doing this for fun (or as 4chan says "for teh lolz") and if I learn something on the way all the better. I took an AI course almost 2 years ago now and I really enjoyed it but I managed to forget everything so this is a way to refresh that. Anyway I want to be able to generate text given a set of inputs. Basically this will read forum inputs (or maybe Twitter tweets) and then generate a comment based on the learning. Now the simplest way would be to use a Markov Chain Text Generator but I want something a little bit more complex than that as the MKC basically only learns by word order (which word is more likely to appear after word x given the input text). I'm trying to see if there's something I can do to make it a little bit more smarter. For example I want it to do something like this: Learn from a large selection of posts in a message board but don't weight it too much For each post: Learn from the other comments in that post and weigh these inputs higher Generate comment and post See what other users' reaction to your post was. If good weigh it positively so you make more posts that are similar to the one made, and vice versa if negative. It's the weighing and learning from mistakes part that I'm not sure how to implement. I thought about Artificial Neural Networks (mainly because I remember enjoying that chapter) but as far as I can tell that's mainly used to classify things (i.e. given a finite set of choices [x1...xn] which x is this given input) not really generate anything. I'm not even sure if this is possible or if it is what should I go about learning/figuring out. What algorithm is best suited for this? To those worried that I will use this as a bot to spam or provide bad answers to SO, I promise that I will not use this to provide (bad) advice or to spam for profit. I definitely will not post it's nonsensical thoughts on SO. I plan to use it for my own amusement. Thanks!

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• Is Google the only OpenID provider that requires "identifier_select"?

  - by Skrat

  I am developing an OpenID consumer in PHP and am using the fantastic LightOpenID library (http://gitorious.org/lightopenid). Basing my code off of that found in the example client script I have successfully created a consumer. However, I've run across a snag: Google requires the openid.identity and openid.claimed_id to be set to "http://specs.openid.net/auth/2.0/identifier_select" (see here). If I do that it works but other providers (i.e. AOL) don't. Here are my questions: Is Google a corner case –– is it the only OpenID provider where identifier_select is required, contrary to the OpenID specs? Is there a shortcoming in the LightOpenID library? Is my understanding of how OpenID works incorrect? If Google is not the only provider that requires identifier_select are there a finite number of them which I'll just hardcode in, or is there someway to determine this through the OpenID spec? I'm new to the internals of OpenID so I wouldn't be surprised if this is a dumb question. I haven't been able to find any info on this subject after scouring the Internet.

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• Generic FSM for game in C++ ?

  - by Mr.Gando

  Hello, I was wondering if there's a way I could code some kind of "generic" FSM for a game with C++?. My game has a component oriented design, so I use a FSM Component. my Finite State Machine (FSM) Component, looks more or less this way. class gecFSM : public gecBehaviour { public: //Constructors gecFSM() { state = kEntityState_walk; } gecFSM(kEntityState s) { state = s; } //Interface void setRule(kEntityState initialState, int inputAction, kEntityState resultingState); void performAction(int action); private: kEntityState fsmTable[MAX_STATES][MAX_ACTIONS]; }; I would love to hear your opinions/ideas or suggestions about how to make this FSM component, generic. With generic I mean: 1) Creating the fsmTable from an xml file is really easy, I mean it's just a bunch of integers that can be loaded to create an MAX_STATESxMAX_ACTION matrix. void gecFSM::setRule(kEntityState initialState, int inputAction, kEntityState resultingState) { fsmTable[initialState][inputAction] = resultingState; } 2) But what about the "perform Action" method ? void gecFSM::performAction(int action) { switch( smTable[ ownerEntity->getState() ][ action ] ) { case WALK: /*Walk action*/ break; case STAND: /*Stand action*/ break; case JUMP: /*Jump action*/ break; case RUN: /*Run action*/ break; } } What if I wanted to make the "actions" and the switch generic? This in order to avoid creating a different FSM component class for each GameEntity? (gecFSMZombie, gecFSMDryad, gecFSMBoss etc ?). That would allow me to go "Data Driven" and construct my generic FSM's from files for example. What do you people suggest?

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• Pecking order of pigeons?

  - by sc_ray

  I was going though problems on graph theory posted by Prof. Ericksson from my alma-mater and came across this rather unique question about pigeons and their innate tendency to form pecking orders. The question goes as follows: Whenever groups of pigeons gather, they instinctively establish a pecking order. For any pair of pigeons, one pigeon always pecks the other, driving it away from food or potential mates. The same pair of pigeons always chooses the same pecking order, even after years of separation, no matter what other pigeons are around. Surprisingly, the overall pecking order can contain cycles—for example, pigeon A pecks pigeon B, which pecks pigeon C, which pecks pigeon A. Prove that any finite set of pigeons can be arranged in a row from left to right so that every pigeon pecks the pigeon immediately to its left. Since this is a question on Graph theory, the first things that crossed my mind that is this just asking for a topological sort of a graphs of relationships(relationships being the pecking order). What made this a little more complex was the fact that there can be cyclic relationships between the pigeons. If we have a cyclic dependency as follows: A-B-C-A where A pecks on B,B pecks on C and C goes back and pecks on A If we represent it in the way suggested by the problem, we have something as follows: C B A But the above given row ordering does not factor in the pecking order between C and A. I had another idea of solving it by mathematical induction where the base case is for two pigeons arranged according to their pecking order, assuming the pecking order arrangement is valid for n pigeons and then proving it to be true for n+1 pigeons. I am not sure if I am going down the wrong track here. Some insights into how I should be analyzing this problem will be helpful. Thanks

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• How do I display a view as if it's the front page via a module?

  - by Justin

  I have a simple view that feeds a home page. I have a custom module that registers some specific URLs in hook_menu that I pass into my module so I can pass them as arguments into the view. I can get the module to display the view all right, but it doesn't use the teaser/is_front view that outputs when I access the home page. I looked through the APIs but I can't seem to figure out how I can output the view via my module as if it's the front page, meaning $is_front is true and the teasers would appear. The reason I'm not passing in the arguments via the URL bar into the view itself is: My argument list is known and finite The argument order is mixed, meaning I will sometimes have /argument1, /argument1/argument2 or just /argument2. I only want to capture the first level URL as an argument for specific, known strings (e.g. I don't want to pass /admin into my view but I do want to pass in /los-angeles, which I register in the menu system via hook_menu in my module) Here are some examples to make this more clear: /admin - loads the admin page /user - loads the login page /boston - passes into the first argument of the view; shows in front/teaser mode / - shows view with no arguments /bread - passes into argument 2 of the view; shows in front/teaser mode /boston/bread - Passes into argument 1 and 2 of the view; shows in front/teaser mode Maybe I'm going about this the wrong way? Or perhaps there is a way to have a module load a view and somehow set front/teaser mode? Details: Drupal 6, PHP 5, MySQL 5, Views, CCK

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• How do I create a class repository in Java and do I really need it?

  - by Roman

  I have a large number of objects which are identified by names (strings). So, I would like to have a kind of mapping from object name to the class instances. I was told that in this situation I can use a "repository" class which works like that: Server myServer = ServerRepository.getServer("NameOfServer"); So, if there is already an object (sever) with the "NameOfServer" it will be returned by the "getServer". If such an object does not exist yet, it will be created and returned by the "getServer". So, my question is how to program such a "repository" class? In this class I have to be able to check if there is an instance of a given class such that it has a given value of a given field. How can I do it? I need to have a kind of loop over all existing object of a given class? Another part of my question is why I cannot use associative arrays (associative container, map, mapping, dictionary, finite map)? (I am not sure how do you call it in Java) In more details, I have an "array" which maps names of objects to objects. So, whenever I create a new object, I add a new element to the array: myArray["NameOfServer"] = new Server("NameOfServer").

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• Which is better Java programming practice: stacking enums and enum constructors, or subclassing?

  - by Arvanem

  Hi folks, Given a finite number of items which differ in kind, is it better to represent them with stacked enums and enum constructors, or to subclass them? Or is there a better approach altogether? To give you some context, in my small RPG program (which ironically is supposed to be simple), a character has different kinds of items in his or her inventory. Items differ based on their type and use and effect. For example, one item of inventory is a spell scroll called Gremlin that adjusts the Utility attribute. Another item might be a sword called Mort that is used in combat and inflicts damage. In my RPG code, I now have tried two ways of representing inventory items. One way was subclassing (for example, InventoryItem - Spell - AdjustingAttributes; InventoryItem - Weapon - Sword) and instantiating each subclass when needed, and assigning values such as names like Gremlin and Mort. The other way was by stacking enums and enum constructors. For example, I created enums for itemCategory and itemSpellTypes and itemWeaponTypes, and the InventoryItem enum was like this: public enum InventoryItem { GREMLIN(itemType.SPELL, itemSpellTypes.ATTRIBUTE, Attribute.UTILITY), MORT(itemType.WEAPON, itemWeaponTypes.SWORD, 30); InventoryItem(itemType typeOfItem, itemSpellTypes spellType, Attribute attAdjusted) { // snip, enum logic here } InventoryItem(itemType typeOfItem, itemWeaponTypes weaponType, int dmg) { // snip, enum logic here } // and so on, for all the permutations of items. } Is there a better Java programming practice than these two approaches? Or if these are the only ways, which of the two is better? Thanks in advance for your suggestions.

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• Fastest way to perform subset test operation on a large collection of sets with same domain

  - by niktech

  Assume we have trillions of sets stored somewhere. The domain for each of these sets is the same. It is also finite and discrete. So each set may be stored as a bit field (eg: 0000100111...) of a relatively short length (eg: 1024). That is, bit X in the bitfield indicates whether item X (of 1024 possible items) is included in the given set or not. Now, I want to devise a storage structure and an algorithm to efficiently answer the query: what sets in the data store have set Y as a subset. Set Y itself is not present in the data store and is specified at run time. Now the simplest way to solve this would be to AND the bitfield for set Y with bit fields of every set in the data store one by one, picking the ones whose AND result matches Y's bitfield. How can I speed this up? Is there a tree structure (index) or some smart algorithm that would allow me to perform this query without having to AND every stored set's bitfield? Are there databases that already support such operations on large collections of sets?

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