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  • Should I define a single "DataContext" and pass references to it around or define muliple "DataConte

    - by Nate Bross
    I have a Silverlight application that consists of a MainWindow and several classes which update and draw images on the MainWindow. I'm now expanding this to keep track of everything in a database. Without going into specifics, lets say I have a structure like this: MainWindow Drawing-Surface Class1 -- Supports Drawing DataContext + DataServiceCollection<T> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) Class3 Each "Class" is passed a reference to the Drawing Surface so they can interact with it independently. I'm starting to use WCF Data Services in Class1 and its working well; however, the other classes are also going to need access to the WCF Data Services. (Should I define my "DataContext" in MainWindow and pass a reference to each child class?) Class1 will need READ access to the "transactions" data, and Class2 will need READ access to some of the drawing data. So my question is, where does it make the most sense to define my DataContext? Does it make sense to: Define a "global" WCF Data Service "Context" object and pass references to that in all of my subsequent classes? Define an instance of the "Context" for each Class1, Class2, etc Have each method that requires access to data define its own instance of the "Context" and use closures handle the async load/complete events? Would a structure like this make more sense? Is there any danger in keeping an active "DataContext" open for an extended period of time? Typical usecase of this application could range from 1 minute to 40+ minutes. MainWindow Drawing-Surface DataContext Class1 -- Supports Drawing DataServiceCollection<DrawingType> w/events Class2 -- Manages "transactions" (add/delete objects from drawing) DataServiceCollection<TransactionType> w/events Class3 DataServiceCollection<T> w/events

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  • remove values from an array php

    - by LiveEn
    I have a array of links and i have another array which contains certain values i would like to filter in the list eg: http://www.liquidshredder.co.uk/shop%3Fkw%3Dsurfboards%26fl%3D330343%26ci%3D3889610385%26network%3Ds http://www.bournemouth-surfing.co.uk/index.php%3FcPath%3D32 http://www.stcstores.co.uk/wetsuit-range-sizing--pricing-info-1-w.asp http://www.kingofwatersports.com/wetsuit-sale-c227.html http://www.uk.best-price.com/search/landing/query/bodyboards/s/google/altk/Surf%2Band/koid/1944273223/ http://www.surfinghardware.co.uk/Results.cfm%3Fcategory%3D20%26kw%3Dbodyboards%26fl%3D11407%26ci%3D3326979552%26network%3Ds http://www.teste.co.uk/adtrack/baod.html http://www.teste.co.uk/bodyboards/ www.sandskater.co.uk/ www.sandskater.co.uk/bodyboards/+Bodyboards&sa=X&ei=GwSWS-KaGM24rAeF-vCKDA&ved=0CBMQHzAKOAo http://www.extremesportstrader.co.uk/buy/water/bodyboarding/ www.extremesportstrader.co.uk/buy/water/bodyboarding/+Bodyboards&sa=X&ei=GwSWS-KaGM24rAeF-vCKDA&ved=0CBYQHzALOAo www.circle-one.co.uk/+Bodyboards&sa=X&ei=GwSWS-KaGM24rAeF-vCKDA&ved=0CBkQHzAMOAo http://www.teste.co.uk/bodyboards/p1 http://www.teste.co.uk/bodyboards/p2 http://www.amazon.co.uk/s/%3Fie%3DUTF8%26keywords%3Dbodyboards%26tag%3Dgooghydr-21%26index%3Daps%26hvadid%3D4764625891%26ref%3Dpd_sl_2lyzsfw1ar_e http://www.teste.co.uk/bodyboards/p3 www.extremesportstrader.co.uk/buy/water/ and i would like to remove all the instances of "http://www.teste.co.uk"? i tried the below code but it doesn't work :( $remove=array("teste.co.uk","127.0.0.1","localhost","wikipedia.org","gmail.com","answers.yahoo.com"); foreach ($list[0] as $key=>$clean) { if (in_array($clean,$remove)) { unset($list[0][$key]); } echo $clean; echo '<br>'; }

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  • Ranking/ weighing search result

    - by biso
    I am trying to build an application that has a smart adaptive search engine (lets say for cars). If I search for for 4x4 then the DB will return all the 4x4 cars I have (100 cars) - but as time goes by and I start checking out cars, liking them, commenting on them, etc the order of the search result should be the different. That means 1 month later when searching for 4x4, I should get the same result set ordered differently as per my previous interaction with the site. If I was mainly liking and commenting on German cars, BMW should be on the top and Land cruiser should be further down. This ranking should be based on attributes that I captureduring user interaction (eg: car origin, user age, user location, car type[4x4, coupe, hatchback], price range). So for each car result I get, I will be weighing it based on how well it is performing on the 5 attributes above. I intend to use the DB just as a repository and do the ranking and the thinking on the server. My question is, what kind of algorithm should I be using to weigh/rank my search result? Thanks.

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  • EC2 persistence of machine

    - by Seagull
    I want to 'persist' my Amazon EC2 images. My scenario: I have a range of Windows and Linux machines Some machines are EBS backed, whereas others are S3 backed. I need to be able to persist a machine (put it to sleep), preferably keeping all settings active I had them when the machine was running. I need to be able to quickly wake up a machine from sleep [Ideally with an SLA of less than 2 min to turn-on, if such an SLA is available with Amazon]. Here's the stuff that confuses me: AWS allows me to put EBS backed machines to sleep, but not S3 backed. I believe I can put S3 machines into some sort of persistence mode. But this involves shutting down the machine, writing it to S3 storage and then recovering from there (not a real sleep mode, but at least I don't continue to get billed for CPU). S3 backing seems to take a long time to either writing a machine to disk, or to recover (turn on a machine). I can't tell immediately which machines are EBS backed and which are S3 backed? It seems like I can instantiate either type, but it's not immediately clear how Amazon decided whether a given machine should be EBS or S3 backed. Advice?

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  • problem with evolutionary algorithms degrading into simulated annealing: mutation too small?

    - by Schnalle
    i have a problem understanding evolutionary algorithms. i tried using this technique several times, but i always ran into the same problem: degeneration into simulated annealing. lets say my initial population, with fitness in brackets, is: A (7), B (9), C (14), D (19) after mating and mutation i have following children: AB (8.3), AC (12.2), AD (14.1), BC(11), BD (14.7), CD (17) after elimination of the weakest, we get A, AB, B, AC next turn, AB will mate again with a result around 8, pushing AC out. next turn, AB again, pushing B out (assuming mutation changes fitness mostly in the 1 range). now, after only a few turns the pool is populated with the originally fittest candidates (A, B) and mutations of those two (AB). this happens regardless of the size of the initial pool, it just takes a bit longer. say, with an initial population of 50 it takes 50 turns, then all others are eliminated, turning the whole setup in a more complicated simulated annealing. in the beginning i also mated canditates with themselves, worsening the problem. so, what do i miss? are my mutation rates simply too small and will it go away if i increase them? here's the project i'm using it for: http://stefan.schallerl.com/simuan-grid-grad/ yeah, the code is buggy and the interface sucks, but i'm too lazy to fix it right now - and be careful, it may lock up your browser. better use chrome, even thought firefox is not slower than chrome for once (probably the tracing for the image comparison pays off, yay!). if anyone is interested, the code can be found here. here i just dropped the ev-alg idea and went for simulated annealing. ps: i'm not even sure about simulated annealing - it is like evolutionary algorithms, just with a population size of one, right?

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  • php fopen function dies, though I have file permissions set to read and write

    - by Matthew Robert Keable
    I'm following a tutorial on php, and am having difficulty getting this to work. I set the appropriate directory permissions to read and write, but every time I run this, I get the die string. The code is: $ourFileName = "testFile.txt"; $ourFileHandle = fopen($ourFileName, 'w') or die("can't open file"); fclose($ourFileHandle); As far as my basic understanding goes, if "testFile.txt" does not exist, fopen should create that file (I have basic knowledge of Python, and remember this same principle in that language). But it...it doesn't. Even if I create the aforementioned file, and put it up, that line of code still returns a die string. My hosting account does not give me permission to execute. Is this a problem? My server runs on Windows. I am using Dreamweaver CS5, on OSX 10.5.8. I've done some searching on this, and see other people having similar issues - but none of them keyed to exactly my range of problems. Being that I'm a beginner, I feel that it might be something I'm overlooking. Thanks!!

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  • Losing URI segments when paginating with CodeIgniter

    - by Danny Herran
    I have a /payments interface where the user should be able to filter via price range, bank, and other stuff. Those filters are standard select boxes. When I submit the filter form, all the post data goes to another method called payments/search. That method performs the validation, saves the post values into a session flashdata and redirects the user back to /payments passing the flashdata name via URL. So my standard pagination links with no filters are exactly like this: payments/index/20/ payments/index/40/ payments/index/60/ And if you submit the filter form, the returning URL is: payments/index/0/b48c7cbd5489129a337b0a24f830fd93 This works just great. If I change the zero for something else, it paginates just fine. The only issue however is that the << 1 2 3 4 page links wont keep the hash after the pagination offset. CodeIgniter is generating the page links ignoring that additional uri segment. My uri_segment config is already set to 3: $config['uri_segment'] = 3; I cannot set the page offset to 4 because that hash may or may not exists. Any ideas of how can I solve this? Is it mandatory for CI to have the offset as the last segment in the uri? Maybe I am trying an incorrect approach, so I am all ears. Thank you folks.

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  • Segmentation in Linux : Segmentation & Paging are redundant?

    - by claws
    Hello, I'm reading "Understanding Linux Kernel". This is the snippet that explains how Linux uses Segmentation which I didn't understand. Segmentation has been included in 80 x 86 microprocessors to encourage programmers to split their applications into logically related entities, such as subroutines or global and local data areas. However, Linux uses segmentation in a very limited way. In fact, segmentation and paging are somewhat redundant, because both can be used to separate the physical address spaces of processes: segmentation can assign a different linear address space to each process, while paging can map the same linear address space into different physical address spaces. Linux prefers paging to segmentation for the following reasons: Memory management is simpler when all processes use the same segment register values that is, when they share the same set of linear addresses. One of the design objectives of Linux is portability to a wide range of architectures; RISC architectures in particular have limited support for segmentation. All Linux processes running in User Mode use the same pair of segments to address instructions and data. These segments are called user code segment and user data segment , respectively. Similarly, all Linux processes running in Kernel Mode use the same pair of segments to address instructions and data: they are called kernel code segment and kernel data segment , respectively. Table 2-3 shows the values of the Segment Descriptor fields for these four crucial segments. I'm unable to understand 1st and last paragraph.

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  • making binned boxplot in matplotlib with numpy and scipy in Python

    - by user248237
    I have a 2-d array containing pairs of values and I'd like to make a boxplot of the y-values by different bins of the x-values. I.e. if the array is: my_array = array([[1, 40.5], [4.5, 60], ...]]) then I'd like to bin my_array[:, 0] and then for each of the bins, produce a boxplot of the corresponding my_array[:, 1] values that fall into each box. So in the end I want the plot to contain number of bins-many box plots. I tried the following: min_x = min(my_array[:, 0]) max_x = max(my_array[:, 1]) num_bins = 3 bins = linspace(min_x, max_x, num_bins) elts_to_bins = digitize(my_array[:, 0], bins) However, this gives me values in elts_to_bins that range from 1 to 3. I thought I should get 0-based indices for the bins, and I only wanted 3 bins. I'm assuming this is due to some trickyness with how bins are represented in linspace vs. digitize. What is the easiest way to achieve this? I want num_bins-many equally spaced bins, with the first bin containing the lower half of the data and the upper bin containing the upper half... i.e., I want each data point to fall into some bin, so that I can make a boxplot. thanks.

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  • TortoiseSVN lists files as modified, but they are identical

    - by BJ Safdie
    I am merging a hot fix from our QA branch back into our Dev branch. Five files have changed. I do a fresh checkout of the Dev branch. I then do a merge (range of revisions) from QA into the Dev working copy. It brings in five files and there is a conflict on an external and ignore property -- which I resolve by "using local" (dev). When I check modifications or commit, I expect to see the five files I merged as the only changes. However, I get close to 700 "modified" files showing up in the commit dialog. If I select one of these file and "Compare with base," WinMerge comes up and says the "files are identical." I have tried this with the file dates set to "last committed" and not. Why are all of these files showing up as modified, when they are identical? What in the merge is causing this? How do I prevent SVN/TortoiseSVN from getting confused this way in the future?

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  • Why does adding Crossover to my Genetic Algorithm give me worse results?

    - by MahlerFive
    I have implemented a Genetic Algorithm to solve the Traveling Salesman Problem (TSP). When I use only mutation, I find better solutions than when I add in crossover. I know that normal crossover methods do not work for TSP, so I implemented both the Ordered Crossover and the PMX Crossover methods, and both suffer from bad results. Here are the other parameters I'm using: Mutation: Single Swap Mutation or Inverted Subsequence Mutation (as described by Tiendil here) with mutation rates tested between 1% and 25%. Selection: Roulette Wheel Selection Fitness function: 1 / distance of tour Population size: Tested 100, 200, 500, I also run the GA 5 times so that I have a variety of starting populations. Stop Condition: 2500 generations With the same dataset of 26 points, I usually get results of about 500-600 distance using purely mutation with high mutation rates. When adding crossover my results are usually in the 800 distance range. The other confusing thing is that I have also implemented a very simple Hill-Climbing algorithm to solve the problem and when I run that 1000 times (faster than running the GA 5 times) I get results around 410-450 distance, and I would expect to get better results using a GA. Any ideas as to why my GA performing worse when I add crossover? And why is it performing much worse than a simple Hill-Climb algorithm which should get stuck on local maxima as it has no way of exploring once it finds a local max?

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  • Select all points in a matrix within 30m of another point

    - by pinnacler
    So if you look at my other posts, it's no surprise I'm building a robot that can collect data in a forest, and stick it on a map. We have algorithms that can detect tree centers and trunk diameters and can stick them on a cartesian XY plane. We're planning to use certain 'key' trees as natural landmarks for localizing the robot, using triangulation and trilateration among other methods, but programming this and keeping data straight and efficient is getting difficult using just Matlab. Is there a technique for sub-setting an array or matrix of points? Say I have 1000 trees stored over 1km (1000m), is there a way to say, select only points within 30m radius of my current location and work only with those? I would just use a GIS, but I'm doing this in Matlab and I'm unaware of any GIS plugins for Matlab. I forgot to mention, this code is going online, meaning it's going on a robot for real-time execution. I don't know if, as the map grows to several miles, using a different data structure will help or if calculating every distance to a random point is what a spatial database is going to do anyway. I'm thinking of mirroring two arrays, one sorted by X and the other by Y. Then bubble sorting to determine the 30m range in that. I do the same for both arrays, X and Y, and then have a third cross link table that will select the individual values. But I don't know, what that's called, how to program that and I'm sure someone already has so I don't want to reinvent the wheel. Cartesian Plane GIS

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  • What's the most efficient query?

    - by Aaron Carlino
    I have a table named Projects that has the following relationships: has many Contributions has many Payments In my result set, I need the following aggregate values: Number of unique contributors (DonorID on the Contribution table) Total contributed (SUM of Amount on Contribution table) Total paid (SUM of PaymentAmount on Payment table) Because there are so many aggregate functions and multiple joins, it gets messy do use standard aggregate functions the the GROUP BY clause. I also need the ability to sort and filter these fields. So I've come up with two options: Using subqueries: SELECT Project.ID AS PROJECT_ID, (SELECT SUM(PaymentAmount) FROM Payment WHERE ProjectID = PROJECT_ID) AS TotalPaidBack, (SELECT COUNT(DISTINCT DonorID) FROM Contribution WHERE RecipientID = PROJECT_ID) AS ContributorCount, (SELECT SUM(Amount) FROM Contribution WHERE RecipientID = PROJECT_ID) AS TotalReceived FROM Project; Using a temporary table: DROP TABLE IF EXISTS Project_Temp; CREATE TEMPORARY TABLE Project_Temp (project_id INT NOT NULL, total_payments INT, total_donors INT, total_received INT, PRIMARY KEY(project_id)) ENGINE=MEMORY; INSERT INTO Project_Temp (project_id,total_payments) SELECT `Project`.ID, IFNULL(SUM(PaymentAmount),0) FROM `Project` LEFT JOIN `Payment` ON ProjectID = `Project`.ID GROUP BY 1; INSERT INTO Project_Temp (project_id,total_donors,total_received) SELECT `Project`.ID, IFNULL(COUNT(DISTINCT DonorID),0), IFNULL(SUM(Amount),0) FROM `Project` LEFT JOIN `Contribution` ON RecipientID = `Project`.ID GROUP BY 1 ON DUPLICATE KEY UPDATE total_donors = VALUES(total_donors), total_received = VALUES(total_received); SELECT * FROM Project_Temp; Tests for both are pretty comparable, in the 0.7 - 0.8 seconds range with 1,000 rows. But I'm really concerned about scalability, and I don't want to have to re-engineer everything as my tables grow. What's the best approach?

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  • A standard set of questions to ask an interviewer?

    - by Rob Wells
    We have had many questions for interviewers to ask interviewees. But none addressing information flow in the other direction, interviewee to interviewer. Just an indirect question about "deal breakers" and one about "finding dream jobs". What I'm after is when you're interviewing at a company do you have a set of questions that you like to ask to help get a feel for the company and the work environment? I have a series of questions that I like to ask that range from the development environment to testing techniques to how the team get on together. Anything else you'd like to ask? Edit: I moved my original list of interviewer questions to my answer below. I've also gone through the other answers and added the ones thought were useful in to that answer. The answer is community wiki so feel free to add anything useful. N.B. This is my first cut of categories. Feel free to modify/add/etc. the categories. Or to recategorise the questions themselves.

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  • How to embed XBase expressions in an Xtext DSL

    - by Marcus Mathioudakis
    I am writing a simple little DSL for specifying constraints on messages, and Have been trying without success for a while to embed XBase expressions into the language. The Grammar looks like this: grammar org.xtext.businessrules.BusinessRules with org.eclipse.xtext.xbase.Xbase //import "http://www.eclipse.org/xtext/xbase/Xbase" as xbase import "http://www.eclipse.org/xtext/common/JavaVMTypes" as jvmTypes generate businessRules "http://www.xtext.org/businessrules/BusinessRules" Start: rules+=Constraint*; Constraint: {Constraint} 'FOR' 'PAYLOAD' payload=PAYLOAD 'ELEMENT' element=ID 'CONSTRAINED BY' constraint=XExpression; PAYLOAD: "SimulationSessionEvents" |"stacons" |"any" ; Range: 'above' min=INT ('below' max=INT)? |'below' max=INT ('above' min=INT)? ; When trying to parse a file such as: FOR PAYLOAD SimulationSessionEvents ELEMENT matrix CONSTRAINED BY ... I can't get it to work for ... = any kind of Arithmetic expression, although it works for ...= loop or if expression, or even just a number. As soon as I do something like '-5' or '4-5' it says Couldn't resolve reference to JvmIdentifiableElement '-', even though the Xbase.xtext Grammar looks like it allows these expressions. I don't think I'm missing any Jars, as it doesn't complain when I run the mwe workflow, but only when trying to parse the input file. Any help would be much appreciated.

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  • Mysql select - improve performance

    - by realshadow
    Hey, I am working on an e-shop which sells products only via loans. I display 10 products per page in any category, each product has 3 different price tags - 3 different loan types. Everything went pretty well during testing time, query execution time was perfect, but today when transfered the changes to the production server, the site "collapsed" in about 2 minutes. The query that is used to select loan types sometimes hangs for ~10 seconds and it happens frequently and thus it cant keep up and its hella slow. The table that is used to store the data has approximately 2 milion records and each select looks like this: SELECT * FROM products_loans WHERE KOD IN("X17/Q30-10", "X17/12", "X17/5-24") AND 369.27 BETWEEN CENA_OD AND CENA_DO; 3 loan types and the price that needs to be in range between CENA_OD and CENA_DO, thus 3 rows are returned. But since I need to display 10 products per page, I need to run it trough a modified select using OR, since I didnt find any other solution to this. I have asked about it here, but got no answer. As mentioned in the referencing post, this has to be done separately since there is no column that could be used in a join (except of course price and code, but that ended very, very badly). Here is the show create table, kod and CENA_OD/CENA_DO very indexed via INDEX. CREATE TABLE `products_loans` ( `KOEF_ID` bigint(20) NOT NULL, `KOD` varchar(30) NOT NULL, `AKONTACIA` int(11) NOT NULL, `POCET_SPLATOK` int(11) NOT NULL, `koeficient` decimal(10,2) NOT NULL default '0.00', `CENA_OD` decimal(10,2) default NULL, `CENA_DO` decimal(10,2) default NULL, `PREDAJNA_CENA` decimal(10,2) default NULL, `AKONTACIA_SUMA` decimal(10,2) default NULL, `TYP_VYHODY` varchar(4) default NULL, `stage` smallint(6) NOT NULL default '1', PRIMARY KEY (`KOEF_ID`), KEY `CENA_OD` (`CENA_OD`), KEY `CENA_DO` (`CENA_DO`), KEY `KOD` (`KOD`), KEY `stage` (`stage`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 And also selecting all loan types and later filtering them trough php doesnt work good, since each type has over 50k records and the select takes too much time as well... Any ides about improving the speed are appreciated.

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  • Enumerate all paths in a weighted graph from A to B where path length is between C1 and C2

    - by awmross
    Given two points A and B in a weighted graph, find all paths from A to B where the length of the path is between C1 and C2. Ideally, each vertex should only be visited once, although this is not a hard requirement. I supose I could use a heuristic to sort the results of the algorithm to weed out "silly" paths (e.g. a path that just visits the same two nodes over and over again) I can think of simple brute force algorithms, but are there any more sophisticed algorithms that will make this more efficient? I can imagine as the graph grows this could become expensive. In the application I am developing, A & B are actually the same point (i.e. the path must return to the start), if that makes any difference. Note that this is an engineering problem, not a computer science problem, so I can use an algorithm that is fast but not necessarily 100% accurate. i.e. it is ok if it returns most of the possible paths, or if most of the paths returned are within the given length range.

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  • Binary Search Tree for specific intent

    - by Luís Guilherme
    We all know there are plenty of self-balancing binary search trees (BST), being the most famous the Red-Black and the AVL. It might be useful to take a look at AA-trees and scapegoat trees too. I want to do deletions insertions and searches, like any other BST. However, it will be common to delete all values in a given range, or deleting whole subtrees. So: I want to insert, search, remove values in O(log n) (balanced tree). I would like to delete a subtree, keeping the whole tree balanced, in O(log n) (worst-case or amortized) It might be useful to delete several values in a row, before balancing the tree I will most often insert 2 values at once, however this is not a rule (just a tip in case there is a tree data structure that takes this into account) Is there a variant of AVL or RB that helps me on this? Scapegoat-trees look more like this, but would also need some changes, anyone who has got experience on them can share some thougts? More precisely, which balancing procedure and/or removal procedure would help me keep this actions time-efficient?

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  • URL shortening: using inode as short name?

    - by Licky Lindsay
    The site I am working on wants to generate its own shortened URLs rather than rely on a third party like tinyurl or bit.ly. Obviously I could keep a running count new URLs as they are added to the site and use that to generate the short URLs. But I am trying to avoid that if possible since it seems like a lot of work just to make this one thing work. As the things that need short URLs are all real physical files on the webserver my current solution is to use their inode numbers as those are already generated for me ready to use and guaranteed to be unique. function short_name($file) { $ino = @fileinode($file); $s = base_convert($ino, 10, 36); return $s; } This seems to work. Question is, what can I do to make the short URL even shorter? On the system where this is being used, the inodes for newly added files are in a range that makes the function above return a string 7 characters long. Can I safely throw away some (half?) of the bits of the inode? And if so, should it be the high bits or the low bits? I thought of using the crc32 of the filename, but that actually makes my short names longer than using the inode. Would something like this have any risk of collisions? I've been able to get down to single digits by picking the right value of "$referencefile". function short_name($file) { $ino = @fileinode($file); // arbitrarily selected pre-existing file, // as all newer files will have higher inodes $ino = $ino - @fileinode($referencefile); $s = base_convert($ino, 10, 36); return $s; }

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  • how to Compute the average probe length for success and failure - Linear probe (Hash Tables)

    - by fang_dejavu
    hi everyone, I'm doing an assignment for my Data Structures class. we were asked to to study linear probing with load factors of .1, .2 , .3, ...., and .9. The formula for testing is: The average probe length using linear probing is roughly Success-- ( 1 + 1/(1-L)**2)/2 or Failure-- (1+1(1-L))/2. we are required to find the theoretical using the formula above which I did(just plug the load factor in the formula), then we have to calculate the empirical (which I not quite sure how to do). here is the rest of the requirements **For each load factor, 10,000 randomly generated positive ints between 1 and 50000 (inclusive) will be inserted into a table of the "right" size, where "right" is strictly based upon the load factor you are testing. Repeats are allowed. Be sure that your formula for randomly generated ints is correct. There is a class called Random in java.util. USE it! After a table of the right (based upon L) size is loaded with 10,000 ints, do 100 searches of newly generated random ints from the range of 1 to 50000. Compute the average probe length for each of the two formulas and indicate the denominators used in each calculationSo, for example, each test for a .5 load would have a table of size approximately 20,000 (adjusted to be prime) and similarly each test for a .9 load would have a table of approximate size 10,000/.9 (again adjusted to be prime). The program should run displaying the various load factors tested, the average probe for each search (the two denominators used to compute the averages will add to 100), and the theoretical answers using the formula above. .** how do I calculate the empirical success?

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  • JavaME - LWUIT images eat up all the memory

    - by Marko
    Hi, I'm writing a MIDlet using LWUIT and images seem to eat up incredible amounts of memory. All the images I use are PNGs and are packed inside the JAR file. I load them using the standard Image.createImage(URL) method. The application has a number of forms and each has a couple of labels an buttons, however I am fairly certain that only the active form is kept in memory (I know it isn't very trustworthy, but Runtime.freeMemory() seems to confirm this). The application has worked well in 240x320 resolution, but moving it to 480x640 and using appropriately larger images for UI started causing out of memory errors to show up. What the application does, among other things, is download remote images. The application seems to work fine until it gets to this point. After downloading a couple of PNGs and returning to the main menu, the out of memory error is encountered. Naturally, I looked into the amount of memory the main menu uses and it was pretty shocking. It's just two labels with images and four buttons. Each button has three images used for style.setIcon, setPressedIcon and setRolloverIcon. Images range in size from 15 to 25KB but removing two of the three images used for every button (so 8 images in total), Runtime.freeMemory() showed a stunning 1MB decrease in memory usage. The way I see it, I either have a whole lot of memory leaks (which I don't think I do, but memory leaks aren't exactly known to be easily tracked down), I am doing something terribly wrong with image handling or there's really no problem involved and I just need to scale down. If anyone has any insight to offer, I would greatly appreciate it.

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  • Scrolling to the bottom of a div on page load: issue with syntaxhighlighter

    - by Rayne
    I've been using this code: var objDiv = document.getElementById("code"); objDiv.scrollTop = objDiv.scrollHeight; to scroll to the very bottom of the div. It worked perfectly in FF and Chrome (I asked a question about it not working in Chrome a few days ago, but it appears the guy who was testing it on Chrome was incorrect, so I tested it myself) until I started syntax highlighting the code that I put in the div with SyntaxHighlighter. Before, I was putting the code in a <p> and breaking lines with <br />, but the <br /> stuff doesn't fly with SyntaxHighlighter, so I replaced all of those with newlines (not entirely certain if this is important, but it's worth mentioning). Now, when the page loads, it does scroll, but not all the way down. It scrolls nearly to the bottom. I've tried all the methods listed in the other question I mentioned but they all do the same thing, or nothing at all. Is there anything else I can try? Here is the relevant piece of the generated HTML. Forgive the poor formatting, I'm not writing the HTML by hand, but rather using Hiccup with Clojure, and it doesn't bother with formatting. <div class="scroll" id="code"><pre class="brush: clojure">=> (doseq [x (range 1 100)] (println x)) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 nil </pre></div><script type="text/javascript">var objDiv = document.getElementById("code"); objDiv.scrollTop = objDiv.scrollHeight;</script>

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  • What are the fastest-performing options for a read-only, unordered collection of unique strings?

    - by Dan Tao
    Disclaimer: I realize the totally obvious answer to this question is HashSet<string>. It is absurdly fast, it is unordered, and its values are unique. But I'm just wondering, because HashSet<T> is a mutable class, so it has Add, Remove, etc.; and so I am not sure if the underlying data structure that makes these operations possible makes certain performance sacrifices when it comes to read operations -- in particular, I'm concerned with Contains. Basically, I'm wondering what are the absolute fastest-performing data structures in existence that can supply a Contains method for objects of type string. Within or outside of the .NET framework itself. I'm interested in all kinds of answers, regardless of their limitations. For example I can imagine that some structure might be restricted to strings of a certain length, or may be optimized depending on the problem domain (e.g., range of possible input values), etc. If it exists, I want to hear about it. One last thing: I'm not restricting this to read-only data structures. Obviously any read-write data structure could be embedded inside a read-only wrapper. The only reason I even mentioned the word "read-only" is that I don't have any requirement for a data structure to allow adding, removing, etc. If it has those functions, though, I won't complain.

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  • python can't start a new thread

    - by Giorgos Komnino
    I am building a multi threading application. I have setup a threadPool. [ A Queue of size N and N Workers that get data from the queue] When all tasks are done I use tasks.join() where tasks is the queue . The application seems to run smoothly until suddently at some point (after 20 minutes in example) it terminates with the error thread.error: can't start new thread Any ideas? Edit: The threads are daemon Threads and the code is like: while True: t0 = time.time() keyword_statuses = DBSession.query(KeywordStatus).filter(KeywordStatus.status==0).options(joinedload(KeywordStatus.keyword)).with_lockmode("update").limit(100) if keyword_statuses.count() == 0: DBSession.commit() break for kw_status in keyword_statuses: kw_status.status = 1 DBSession.commit() t0 = time.time() w = SWorker(threads_no=32, network_server='http://192.168.1.242:8180/', keywords=keyword_statuses, cities=cities, saver=MySqlRawSave(DBSession), loglevel='debug') w.work() print 'finished' When the daemon threads are killed? When the application finishes or when the work() finishes? Look at the thread pool and the worker (it's from a recipe ) from Queue import Queue from threading import Thread, Event, current_thread import time event = Event() class Worker(Thread): """Thread executing tasks from a given tasks queue""" def __init__(self, tasks): Thread.__init__(self) self.tasks = tasks self.daemon = True self.start() def run(self): '''Start processing tasks from the queue''' while True: event.wait() #time.sleep(0.1) try: func, args, callback = self.tasks.get() except Exception, e: print str(e) return else: if callback is None: func(args) else: callback(func(args)) self.tasks.task_done() class ThreadPool: """Pool of threads consuming tasks from a queue""" def __init__(self, num_threads): self.tasks = Queue(num_threads) for _ in range(num_threads): Worker(self.tasks) def add_task(self, func, args=None, callback=None): ''''Add a task to the queue''' self.tasks.put((func, args, callback)) def wait_completion(self): '''Wait for completion of all the tasks in the queue''' self.tasks.join() def broadcast_block_event(self): '''blocks running threads''' event.clear() def broadcast_unblock_event(self): '''unblocks running threads''' event.set() def get_event(self): '''returns the event object''' return event

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  • TSQL - make a literal float value

    - by David B
    I understand the host of issues in comparing floats, and lament their use in this case - but I'm not the table author and have only a small hurdle to climb... Someone has decided to use floats as you'd expect GUIDs to be used. I need to retrieve all the records with a specific float value. sp_help MyTable -- Column_name Type Computed Length Prec -- RandomGrouping float no 8 53 Here's my naive attempt: --yields no results SELECT RandomGrouping FROM MyTable WHERE RandomGrouping = 0.867153569942739 And here's an approximately working attempt: --yields 2 records SELECT RandomGrouping FROM MyTable WHERE RandomGrouping BETWEEN 0.867153569942739 - 0.00000001 AND 0.867153569942739 + 0.00000001 -- 0.867153569942739 -- 0.867153569942739 In my naive attempt, is that literal a floating point literal? Or is it really a decimal literal that gets converted later? If my literal is not a floating point literal, what is the syntax for making a floating point literal? EDIT: Another possibility has occurred to me... it may be that a more precise number than is displayed is stored in this column. It may be impossible to create a literal that represents this number. I will accept answers that demonstrate that this is the case. EDIT: response to DVK. TSQL is MSSQLServer's dialect of SQL. This script works, and so equality can be performed deterministically between float types: DECLARE @X float SELECT top 1 @X = RandomGrouping FROM MyTable WHERE RandomGrouping BETWEEN 0.839110948199148 - 0.000000000001 AND 0.839110948199148 + 0.000000000001 --yields two records SELECT * FROM MyTable WHERE RandomGrouping = @X I said "approximately" because that method tests for a range. With that method I could get values that are not equal to my intended value. The linked article doesn't apply because I'm not (intentionally) trying to straddle the world boundaries between decimal and float. I'm trying to work with only floats. This isn't about the non-convertibility of decimals to floats.

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