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  • Is there "good" PRNG generating values without hidden state?

    - by actual
    I need some good pseudo random number generator that can be computed like a pure function from its previous output without any state hiding. Under "good" I mean: I must be able to parametrize generator in such way that running it for 2^n iterations with any parameters should cover all or almost all values between 0 and 2^n - 1, where n is the number of bits in output value. Combined generator output of n + p bits must cover all or almost all values between 0 and 2^(n + p) - 1 if I run it for 2^n iterations for every possible combination of its parameters, where p is the number of bits in parameters. For example, LCG can be computed like a pure function and it can meet first condition, but it can not meet second one. Say, we have 32-bit generator, m = 2^32 and it is constant, our p = 64 (two 32-bit parameters a and c), n + p = 96, so we must peek data by three ints from output to meet second condition. Unfortunately, condition can not be meet because of strictly alternating sequence of odd and even ints in output. To overcome this, hidden state must be introduced, but that makes function not pure and breaks first condition (period become much longer). Am I wanting too much?

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  • Why do I get errors when using unsigned integers in an expression with C++?

    - by neuviemeporte
    Given the following piece of (pseudo-C++) code: float x=100, a=0.1; unsigned int height = 63, width = 63; unsigned int hw=31; for (int row=0; row < height; ++row) { for (int col=0; col < width; ++col) { float foo = x + col - hw + a * (col - hw); cout << foo << " "; } cout << endl; } The values of foo are screwed up for half of the array, in places where (col - hw) is negative. I figured because col is int and comes first, that this part of the expression is converted to int and becomes negative. Unfortunately, apparently it doesn't, I get an overflow of an unsigned value and I've no idea why. How should I resolve this problem? Use casts for the whole or part of the expression? What type of casts (C-style or static_cast<...)? Is there any overhead to using casts (I need this to work fast!)? EDIT: I changed all my unsigned ints to regular ones, but I'm still wondering why I got that overflow in this situation.

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  • Strange behaviour of CheckBox and TwoWay bound property

    - by walkor
    Hello, everyone. I fell in the following situation: I have a main UserControl with a DataGrid (which contains List). I need to show different panels depending on properties of the selected row(object). So i've created 2 controls and included them into this main control. Main control has 2 public properties - public List<ComplexObject> SourceList { get; set; } and public ComplexObject CurrentObject { get; set; } Pseudo-code: <UserControl x:Name="Main"> <DataGrid ItemsSource="{Binding SourceList}" SelectedItem="{Binding CurrentObject, Mode=TwoWay}"/> <Controls:RightPanelFirst Visibility="condition2"/> <Controls:RightPanelSecond Visibility="condition2"/> </UserControl> RightPanelFirst and RightPanelSecond have the following xaml: <UserControl> <... content here...> <CheckBox IsChecked="{Binding CurrentObject.ComplexProperty.SimpleProperty1, Mode=TwoWay}"> <CheckBox IsChecked="{Binding CurrentObject.ComplexProperty.SimpleProperty2, Mode=TwoWay}" x:Name="cbSecond"> <TextBox IsEnabled="{Binding IsChecked, ElementName=cbSecond}"/> </UserControl> So, my actual steps: Check both checkboxes (object values are set to true) Make other actions in code behind which modify CurrentObject. Then i want UI to reflect the changes, so I call NotifyPropertyChanged("CurrentObject"); SimpleProperty1 remains the same, but SimpleProperty2 resets to false I have no idea why this happens, can anyone help me please? Silverlight drives me mad.

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  • Why am I getting a EXC_BAD_ACCESS in a NSTimer selector?

    - by AngeDeLaMort
    I've got quite a weird problem. To make it short, i'll write some pseudo-code: init: create a dictionary and insert n elements. create a "repeat timer" and add it to the currentRunLoop using the timerRefresh selector. timerRefresh: using a list of keys, find the items in the dictionary if the item exists -> call a function So, for an unknown reason, I get an EXC_BAD_ACCESS when I do: [item function]; But I traced the address I got from the dictionary items and it's ok. The ref count of the items in the dictionary is still 1. The {release, dealloc} of the items in the dictionary aren't called. Everything seems fine. Also, to make it worst, it works for some items. So, I'm wondering if there is a threading problem? or something else obscure? The callstack is quite simple: #0 0x93e0604b in objc_msgSend_fpret #1 0x00f3e6b0 in ?? #2 0x0001cfca in -[myObject functionm:] at myObject.m:000 #3 0x305355cd in __NSFireTimer #4 0x302454a0 in CFRunLoopRunSpecific #5 0x30244628 in CFRunLoopRunInMode #6 0x32044c31 in GSEventRunModal #7 0x32044cf6 in GSEventRun #8 0x309021ee in UIApplicationMain #9 0x000027e0 in main at main.m:14 So, any suggestion where to look would be appreciated.

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  • Using the Queue class in Python 2.6

    - by voipme
    Let's assume I'm stuck using Python 2.6, and can't upgrade (even if that would help). I've written a program that uses the Queue class. My producer is a simple directory listing. My consumer threads pull a file from the queue, and do stuff with it. If the file has already been processed, I skip it. The processed list is generated before all of the threads are started, so it isn't empty. Here's some pseudo-code. import Queue, sys, threading processed = [] def consumer(): while True: file = dirlist.get(block=True) if file in processed: print "Ignoring %s" % file else: # do stuff here dirlist.task_done() dirlist = Queue.Queue() for f in os.listdir("/some/dir"): dirlist.put(f) max_threads = 8 for i in range(max_threads): thr = Thread(target=consumer) thr.start() dirlist.join() The strange behavior I'm getting is that if a thread encounters a file that's already been processed, the thread stalls out and waits until the entire program ends. I've done a little bit of testing, and the first 7 threads (assuming 8 is the max) stop, while the 8th thread keeps processing, one file at a time. But, by doing that, I'm losing the entire reason for threading the application. Am I doing something wrong, or is this the expected behavior of the Queue/threading classes in Python 2.6?

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  • Optimally place a pie slice in a rectangle.

    - by Lisa
    Given a rectangle (w, h) and a pie slice with start angle and end angle, how can I place the slice optimally in the rectangle so that it fills the room best (from an optical point of view, not mathematically speaking)? I'm currently placing the pie slice's center in the center of the rectangle and use the half of the smaller of both rectangle sides as the radius. This leaves plenty of room for certain configurations. Examples to make clear what I'm after, based on the precondition that the slice is drawn like a unit circle: A start angle of 0 and an end angle of PI would lead to a filled lower half of the rectangle and an empty upper half. A good solution here would be to move the center up by 1/4*h. A start angle of 0 and an end angle of PI/2 would lead to a filled bottom right quarter of the rectangle. A good solution here would be to move the center point to the top left of the rectangle and to set the radius to the smaller of both rectangle sides. This is fairly easy for the cases I've sketched but it becomes complicated when the start and end angles are arbitrary. I am searching for an algorithm which determines center of the slice and radius in a way that fills the rectangle best. Pseudo code would be great since I'm not a big mathematician.

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  • is this a design pattern?

    - by Michel
    Hi all, i have to build some financial data report, and for making the calculation, there are a lot of 'if then' situations: if it's a large client, subtract 10%, if it's postal code equals '10101', add 10%, if the day is on a saturday, make a difficult calculation etc. so i once read about this kind of example, and what they did was (hope i remember well) create a class with some base info and make it possible to add all kinds of calculationobjects to it. So to put what i remembered in pseudo code Basecalc bc = new baseCalc(); //put the info in the bc so other objects can do their if bc.Add(new Largecustomercalc()); bc.Add(new PostalcodeCalc()); bc.add(new WeekdayCalc()); the the bc would run the Calc() methods of all of the added Calc objects. As i type this i think all the Calc objects must be able to see the Basecalc properties to correctly perform their calculation logic. So all the if's are in the different Calc objects and not ALL in the Basecalc. does this make sense? I was wondering if this is some kind of design pattern?

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  • Questions about the Backpropogation Algorithm

    - by Colemangrill
    I have a few questions concerning backpropogation. I'm trying to learn the fundamentals behind neural network theory and wanted to start small, building a simple XOR classifier. I've read a lot of articles and skimmed multiple textbooks - but I can't seem to teach this thing the pattern for XOR. Firstly, I am unclear about the learning model for backpropogation. Here is some pseudo-code to represent how I am trying to train the network. [Lets assume my network is setup properly (ie: multiple inputs connect to a hidden layer connect to an output layer and all wired up properly)]. SET guess = getNetworkOutput() // Note this is using a sigmoid activation function. SET error = desiredOutput - guess SET delta = learningConstant * error * sigmoidDerivative(guess) For Each Node in inputNodes For Each Weight in inputNodes[n] inputNodes[n].weight[j] += delta; // At this point, I am assuming the first layer has been trained. // Then I recurse a similar function over the hidden layer and output layer. // The prime difference being that it further divi's up the adjustment delta. I realize this is probably not enough to go off of, and I will gladly expound on any part of my implementation. Using the above algorithm, my neural network does get trained, kind of. But not properly. The output is always XOR 1 1 [smallest number] XOR 0 0 [largest number] XOR 1 0 [medium number] XOR 0 1 [medium number] I can never train the [1,1] [0,0] to be the same value. If you have any suggestions, additional resources, articles, blogs, etc for me to look at I am very interested in learning more about this topic. Thank you for your assistance, I appreciate it greatly!

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  • Groovy & Grails Concurrency ( quartz, executor )

    - by Pietro
    What I'm trying to do is to run multiple threads at some starting time. Those threads must stay alive for 90minutes after start. During the 90minutes they execute something after a random sleep time (ex: 5minutes to 15minutes). Here is a pseudo code on how I would implement it. The problem is that doing it in this way the threads run in an unexpected way. How can I implement correctly something like this? Class MyJob { static triggers = { cron name: 'first', cronExpression: "0 30 21 * * FRI" cron name: 'second', cronExpression: "0 30 19 * * FRI" cron name: 'third', cronExpression: "0 30 17 * * FRI" def myService def execute() { switch( between trigger name ) case 'first': model = Model.findByAttribute(...) ... myService.run( model, start_time ) break; ... } } class MyService { def run( model, start_time ) { def end_time = end_time.plusMinutes(90) model.fields.each( field -> Thread.start { executeSomeTasks( field, start_time, end_time ) } ) } def executeSomeTasks( field, start_time, end_time ) { while( start_time < end_time ) { ...do something ... sleep( Random.nextInt( 1000 ) ); } } }

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  • Virtual audio driver (microphone)

    - by Dalamber
    Hello guys, I want to develop a virtual microphone driver. Please, do not say anything about DirectShow - that's not "the way". I need a solution that will work with any software including Skype and MSN. And DirectShow doesn't fit these requirements. I found AVStream Filter-Centric Simulated Capture Driver (avssamp.sys) in Windows 7 WDK. What I need is an audio part of it. By default it reads avssamp.wav and plays it. But this driver is registered as WDM streaming capture device. And I want it in Audio Capture Device. There are some posts in the web but they are all the same: http://www.tech-archive.net/Archive/Development/microsoft.public.development.device.drivers/2005-05/msg00124.html http://www.winvistatips.com/problem-installing-avssamp-audio-capture-sources-category-t184898.html I think registering this filter-driver as audio capture device will make Skype recognize it as a microphone and thefore I will be able to push any PCM file as if it goes from mic. If someone already faced this problem before, please help. Thanks in advance.

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  • Big-O for GPS data

    - by HH
    A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is an arbitrary constants Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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  • Uncommitted reads in SSIS

    - by OldBoy
    I'm trying to debug some legacy Integration Services code, and really want some confirmation on what I think the problem is: We have a very large data task inside a control flow container. This control flow container is set up with TransactionOption = supported - i.e. it will 'inherit' transactions from parent containers, but none are set up here. Inside the data flow there is a call to a stored proc that writes to a table with pseudo code something like: "If a record doesn't exist that matches these parameters then write it" Now, the issue is that there are three records being passed into this proc all with the same parameters, so logically the first record doesn't find a match and a record is created. The second record (with the same parameters) also doesn't find a match and another record is created. My understanding is that the first 'record' passed to the proc in the dataflow is uncommitted and therefore can't be 'read' by the second call. The upshot being that all three records create a row, when logically only the first should. In this scenario am I right in thinking that it is the uncommitted transaction that stops the second call from seeing the first? Even setting the isolation level on the container doesn't help because it's not being wrapped in a transaction anyway.... Hope that makes sense, and any advice gratefully received. Work-arounds confer god-like status on you.

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  • Auto scale and rotate images

    - by Dave Jarvis
    Given: two images of the same subject matter; the images have the same resolution, colour depth, and file format; the images differ in size and rotation; and two lists of (x, y) co-ordinates that correlate the images. I would like to know: How do you transform the larger image so that it visually aligns to the second image? (Optional.) What are the minimum number of points needed to get an accurate transformation? (Optional.) How far apart do the points need to be to get an accurate transformation? The transformation would need to rotate, scale, and possibly shear the larger image. Essentially, I want to create (or find) a program that does the following: Input two images (e.g., TIFFs). Click several anchor points on the small image. Click the several corresponding anchor points on the large image. Transform the large image such that it maps to the small image by aligning the anchor points. This would help align pictures of the same stellar object. (For example, a hand-drawn picture from 1855 mapped to a photograph taken by Hubble in 2000.) Many thanks in advance for any algorithms (preferably Java or similar pseudo-code), ideas or links to related open-source software packages.

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  • How to combine apache requests?

    - by Bruce
    To give you the situation in abstract: I have an ajax client that often needs to retrieve 3-10 static documents from the server. Those 3-10 documents are selected by the client out of about 100 documents in total. I have no way of knowing in advance which 3-10 documents the client will require. Additionally, those 100 documents are generated from database content, and so change over time. It seems messy to me to have to make 10 ajax requests for 10 separate documents. My first thought was to write a jsp that could use the include action. ie in pseudo code for (param in params){ jsp:include page="[param]" } But it turns out the tomcat doesn't just include the html resource, it recompiles it, generating a class file every time, which also seems wasteful. Does any one know of a neat solution for combining apache requests to static files to make one request, rather than several, but without the overhead of, for example, tomcat generating extra class files for each static file and regenerating them each time the static file changes? Thanks! Hopefully my question is clear - it's a bit long-winded.

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  • Pre Project Documentation

    - by DeanMc
    I have an issue that I feel many programmers can relate to... I have worked on many small scale projects. After my initial paper brain storm I tend to start coding. What I come up with is usually a rough working model of the actual application. I design in a disconnected fashion so I am talking about underlying code libraries, user interfaces are the last thing as the library usually dictates what is needed in the UI. As my projects get bigger I worry that so should my "spec" or design document. The above paragraph, from my investigations, is echoed all across the internet in one fashion or another. When a UI is concerned there is a bit more information but it is UI specific and does not relate to code libraries. What I am beginning to realise is that maybe code is code is code. It seems from my extensive research that there is no 1:1 mapping between a design document and the code. When I need to research a topic I dump information into OneNote and from there I prioritise features into versions and then into related chunks so that development runs in a fairly linear fashion, my tasks tend to look like so: Implement Binary File Reader Implement Binary File Writer Create Object to encapsulate Data for expression to the caller Now any programmer worth his salt is aware that between those three to do items could be a potential wall of code that could expand out to multiple files. I have tried to map the complete code process for each task but I simply don't think it can be done effectively. By the time one mangles pseudo code it is essentially code anyway so the time investment is negated. So my question is this: Am I right in assuming that the best documentation is the code itself. We are all in agreement that a high level overview is needed. How high should this be? Do you design to statement, class or concept level? What works for you?

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  • OpenMP: Get total number of running threads

    - by Konrad Rudolph
    I need to know the total number of threads that my application has spawned via OpenMP. Unfortunately, the omp_get_num_threads() function does not work here since it only yields the number of threads in the current team. However, my code runs recursively (divide and conquer, basically) and I want to spawn new threads as long as there are still idle processors, but no more. Is there a way to get around the limitations of omp_get_num_threads and get the total number of running threads? If more detail is required, consider the following pseudo-code that models my workflow quite closely: function divide_and_conquer(Job job, int total_num_threads): if job.is_leaf(): # Recurrence base case. job.process() return left, right = job.divide() current_num_threads = omp_get_num_threads() if current_num_threads < total_num_threads: # (1) #pragma omp parallel num_threads(2) #pragma omp section divide_and_conquer(left, total_num_threads) #pragma omp section divide_and_conquer(right, total_num_threads) else: divide_and_conquer(left, total_num_threads) divide_and_conquer(right, total_num_threads) job = merge(left, right) If I call this code with a total_num_threads value of 4, the conditional annotated with (1) will always evaluate to true (because each thread team will contain at most two threads) and thus the code will always spawn two new threads, no matter how many threads are already running at a higher level. I am searching for a platform-independent way of determining the total number of threads that are currently running in my application.

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  • VLC ActivX plugin not playing video in update IE9

    - by Prashant Mehta
    I am using vlc ActiveX plugin on web browser IE9 to play video live streaming. Its work perfect in IE8 but when I update browser from IE8 to IE9 than it not playing video file or live straming. here is my code. <object type="application/x-vlc-plugin" id="vlc" width="517" height="388" classid="clsid:9BE31822-FDAD-461B-AD51-BE1D1C159921"> <param name="MRL" id="mrlVideo" value="" /> <param name="volume" value="50" /> <param name="autoplay" value="True" /> <param name="loop" value="false" /> <param name="fullscreen" value="false" /> <param name="wmode" value="transparent" /> <param name="toolbar" value="true" /> <param name="windowless" value="true" /> </object> and in javascript I am using these var vlc = document.getElementById("vlc"); var options = new Array(":rtsp-tcp"); var urlVideofile = "hppt://IP:portnumber/" var id = vlc.playlist.add(urlVideofile, null, options); vlc.playlist.playItem(id); Here is attach image that showing what exactly error is coming Any help is greatly appreciated Thanks.

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  • Web Audio API and mobile browsers

    - by Michael
    I've run into a problem while implementing sound and music into an HTML game that I'm building. I'm using the Web Audio API, loading all the sound files with XMLHttpRequests and decoding them into an AudioBufferSourceNode with AudioContext.prototype.decodeAudioData(). It looks something like this: var request = new XMLHttpRequest(); request.open("GET", "soundfile.ogg", true); request.responseType = "arraybuffer"; request.onload = function() { context.decodeAudioData(request.response) } request.send(); Everything plays fine, but on mobile the decodeAudioData takes an absurdly long time for the background music. I then tried using AudioContext.prototype.createMediaElementSource() to load the music from an HTML Audio object, since they support streaming and don't have to load the whole file into memory at once. It looked something like this: var audio = new Audio('soundfile.ogg'); var source = context.createMediaElementSource(audio); var mainVolume = context.createGain(); source.connect(mainVolume); mainVolume.connect(context.destination); This loads much faster, but the audio volume isn't affected by the gain node. Works fine on desktop, so I'm assuming this is a bug/limitation of mobile Chrome (testing on Android). Is there actually no good, well-performing way to handle sound on mobile browsers or am just I doing something stupid?

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  • How can I make hundreds of simultaneously running processes communicate with a database through one

    - by Olfan
    Long speech short: How can I make hundreds of simultaneously running processes communicate with a database through one or few permanent sessions? The whole story: I once built a number crunching engine that handles vast amounts of large data files by forking off one child after another giving each a small number of files to work on. File locking, progress monitoring and result propagation happen in an Oracle database which all (sub-)processes access at various times using an application-specific module which encapsulates DBI. This worked well at first, but now with higher volumes of input data, the number of database sessions (one per child, and they can be very short-lived) constantly being opened and closed is becoming an issue. I now want to centralise database access so that there are only one or few fixed database sessions which handle all database access for all the (sub-)processes. The presence of the database abstraction module should make the changes easy because the function calls in the worker instances can stay the same. My problem is that I cannot think of a suitable way to enhance said module in order to establish communication between all the processes and the database connector(s). I thought of message queueing, but couldn't come up with a way of connecting a large herd of requestors with one or few database connectors in a way so that bidirectional communication is possible (for collecting the query result). An asynchronous approach could help here in that all requests are written to the same queue and the database connector servicing the request will "call back" to submit the result. But my mind fails me in generating an image clear enough so that I can paint into code. Threading instead of forking might have given me an easier start, but this would now require massive changes to the code base that I'm not prepared to do to a live system. The more I think of it, the more the base idea looks like a pre-forked web server to me only that it doesn't serve web pages but database queries. Any ideas on what to dig into, and where? Sample (pseudo) code to inspire me, links to possibly related articles, ready solutions on CPAN maybe?

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  • Array, change color, as3

    - by pixelGreaser
    Hi Thanks for the help Yesterday, but I have on more question. How can I change color of text on certain words? My animation plays the text animation of THIS SALE IS RED HOT!!! I want RED HOT it to be red. It seems the array can be indexed in such a way to switch the color from Blue to Red. MY BANNER ADD var myArray:Array = ["THIS","SALE","IS","RED HOT!!!",]; var tm:Timer = new Timer(500); tm.addEventListener(TimerEvent.TIMER, countdown); function countdown(event:TimerEvent) { tx.text = myArray[(tm.currentCount-1)%myArray.length]; } tm.start(); tx.textColor = 0x0000FF; Cont...PSEUDO CODE //var myArray:Array = ["This","Sale","is","RED HOT!!!",]; var spliceRedhot = myArray.splice(-1); //trace(myArray[2]); trace(spliceRedhot); function mySplice(e:Event):void{ if (spliceRedhot = 4){ //Make RED HOT!!! red tx.textColor = 0xFF0000; } else{ //Text is Blue again tx.textColor = 0x0000FF; } }

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  • How to change Hibernate´s auto persistance strategy

    - by Kristofer Borgstrom
    I just noted that my hibernate entities are automatically persisted to the database (or at least to cache) before I call any save() or update() method. To me this is a pretty strange default behavior but ok, as long as I can disable it, it´s fine. The problem I have is I want to update my entity´s state (from 1 to 2) only if the entity in the database still has the state it had when I retrieved [1] (this is to eliminate concurrency issues when another server is updating this same object). For this reason I have created a custom NamedQuery that will only update the entity if state is 1. So here is some pseudo-code: //Get the entity Entity item = dao.getEntity(); item.getState(); //==1 //Update the entity item.setState(2); //Here is the problem, this effectively changes the state of my entity braking my query that verifies that state is still == 1. dao.customUpdate(item); //Returns 0 rows changes since state != 1. So, how do I make sure the setters don´t change the state in cache/db? Thanks, Kristofer

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  • How to delete duplicate/aggregate rows faster in a file using Java (no DB)

    - by S. Singh
    I have a 2GB big text file, it has 5 columns delimited by tab. A row will be called duplicate only if 4 out of 5 columns matches. Right now, I am doing dduping by first loading each coloumn in separate List , then iterating through lists, deleting the duplicate rows as it encountered and aggregating. The problem: it is taking more than 20 hours to process one file. I have 25 such files to process. Can anyone please share their experience, how they would go about doing such dduping? This dduping will be a throw away code. So, I was looking for some quick/dirty solution, to get job done as soon as possible. Here is my pseudo code (roughly) Iterate over the rows i=current_row_no. Iterate over the row no. i+1 to last_row if(col1 matches //find duplicate && col2 matches && col3 matches && col4 matches) { col5List.set(i,get col5); //aggregate } Duplicate example A and B will be duplicate A=(1,1,1,1,1), B=(1,1,1,1,2), C=(2,1,1,1,1) and output would be A=(1,1,1,1,1+2) C=(2,1,1,1,1) [notice that B has been kicked out]

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  • Average over a timeframe with missing data

    - by BHare
    Assuming a table such as: UID Name Datetime Users 4 Room 4 2012-08-03 14:00:00 3 2 Room 2 2012-08-03 14:00:00 3 3 Room 3 2012-08-03 14:00:00 1 1 Room 1 2012-08-03 14:00:00 2 3 Room 3 2012-08-03 14:15:00 1 2 Room 2 2012-08-03 14:15:00 4 1 Room 1 2012-08-03 14:15:00 3 1 Room 1 2012-08-03 14:30:00 6 1 Room 1 2012-08-03 14:45:00 3 2 Room 2 2012-08-03 14:45:00 7 3 Room 3 2012-08-03 14:45:00 8 4 Room 4 2012-08-03 14:45:00 4 I wanted to get the average user count of each room (1,2,3,4) from the time 2PM to 3PM. The problem is that sometimes the room may not "check in" at the 15 minute interval time, so the assumption has to be made that the previous last known user count is still valid. For example the check-in's for 2012-08-03 14:15:00 room 4 never checked in, so it must be assumed that room 4 had 3 users at 2012-08-03 14:15:00 because that is what it had at 2012-08-03 14:00:00 This follows on through so that the average user count I am looking for is as follows: Room 1: (2 + 3 + 6 + 3) / 4 = 3.5 Room 2: (3 + 4 + 4 + 7) / 4 = 4.5 Room 3: (1 + 1 + 1 + 8) / 4 = 2.75 Room 4: (3 + 3 + 3 + 4) / 4 = 3.25 where # is the assumed number based on the previous known check-in. I am wondering if it's possible to so this with SQL alone? if not I am curious of a ingenious PHP solution that isn't just bruteforce math, as such as my quick inaccurate pseudo code: foreach ($rooms_id_array as $room_id) { $SQL = "SELECT * FROM `table` WHERE (`UID` == $room_id && `Datetime` >= 2012-08-03 14:00:00 && `Datetime` <= 2012-08-03 15:00:00)"; $result = query($SQL); if ( count($result) < 4 ) { // go through each date and find what is missing, and then go to previous date and use that instead } else { foreach ($result) $sum += $result; $avg = $sum / 4; } }

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  • Invoking different methods on threads

    - by Kraken
    I have a main process main. It creates 10 threads (say) and then what i want to do is the following: while(required){ Thread t= new Thread(new ClassImplementingRunnable()); t.start(); counter++; } Now i have the list of these threads, and for each thread i want to do a set of process, same for all, hence i put that implementation in the run method of ClassImplementingRunnable. Now after the threads have done their execution, i wan to wait for all of them to stop, and then evoke them again, but this time i want to do them serially not in parallel. for this I join each thread, to wait for them to finish execution but after that i am not sure how to evoke them again and run that piece of code serially. Can i do something like for(each thread){ t.reevoke(); //how can i do that. t.doThis(); // Also where does `dothis()` go, given that my ClassImplementingRunnable is an inner class. } Also, i want to use the same thread, i.e. i want the to continue from where they left off, but in a serial manner. I am not sure how to go about the last piece of pseudo code. Kindly help. Working with with java.

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  • JavaCC: How can I specify which token(s) are expected in certain context?

    - by java.is.for.desktop
    Hello, everyone! I need to make JavaCC aware of a context (current parent token), and depending on that context, expect different token(s) to occur. Consider the following pseudo-code: TOKEN <abc> { "abc*" } // recognizes "abc", "abcd", "abcde", ... TOKEN <abcd> { "abcd*" } // recognizes "abcd", "abcde", "abcdef", ... TOKEN <element1> { "element1" "[" expectOnly(<abc>) "]" } TOKEN <element2> { "element2" "[" expectOnly(<abcd>) "]" } ... So when the generated parser is "inside" a token named "element1" and it encounter "abcdef" it recognizes it as <abc>, but when its "inside" a token named "element2" it recognizes the same string as <abcd>. element1 [ abcdef ] // aha! it can only be <abc> element2 [ abcdef ] // aha! it can only be <abcd> If I'm not wrong, it would behave similar to more complex DTD definitions of an XML file. So, how can one specify, in which "context" which token(s) are valid/expected? NOTE: It would be not enough for my real case to define a kind of "hierarchy" of tokens, so that "abcdef" is always first matched against <abcd> and than <abc>. I really need context-aware tokens.

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