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  • Throughput measurements

    - by dotsid
    I wrote simple load testing tool for testing performance of Java modules. One problem I faced is algorithm of throughput measurements. Tests are executed in several thread (client configure how much times test should be repeated), and execution time is logged. So, when tests are finished we have following history: 4 test executions 2 threads 36ms overall time - idle * test execution 5ms 9ms 4ms 13ms T1 |-*****-*********-****-*************-| 3ms 6ms 7ms 11ms T2 |-***-******-*******-***********-----| <-----------------36ms---------------> For the moment I calculate throughput (per second) in a following way: 1000 / overallTime * threadCount. But there is problem. What if one thread will complete it's own tests more quickly (for whatever reason): 3ms 3ms 3ms 3ms T1 |-***-***-***-***----------------| 3ms 6ms 7ms 11ms T2 |-***-******-*******-***********-| <--------------32ms--------------> In this case actual throughput is much better because of measured throughput is bounded by the most slow thread. So, my question is how should I measure throughput of code execution in multithreaded environment.

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  • determine if intersection of a set with conjunction of two other sets is empty

    - by koen
    For any three given sets A, B and C: is there a way to determine (programmatically) whether there is an element of A that is part of the conjunction of B and C? example: A: all numbers greater than 3 B: all numbers lesser than 7 C: all numbers that equal 5 In this case there is an element in set A, being the number 5, that fits. I'm implementing this as specifications, so this numerical range is just an example. A, B, C could be anything.

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  • RijndaelManaged Padding when data matches block size

    - by trampster
    If I use PKCS7 padding in RijndaelManaged with 16 bytes of data then I get 32 bytes of data output. It appears that for PKCS7 when the data size matches the block size it adds a whole extra block of data. If I use Zeros padding for 16 bytes of data I get out 16 bytes of data. So for Zeros padding if the data matches the block size then it doesn't pad. I have searched through the documentation and it says nothing about this difference in padding behavior. Can someone please point me to some kind of documentation which specifies what the padding behavior should be for the different padding modes when the data size matches the block size.

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  • Could a truly random number be generated using pings to psuedo-randomly selected IP addresses?

    - by _ande_turner_
    The question posed came about during a 2nd Year Comp Science lecture while discussing the impossibility of generating numbers in a deterministic computational device. This was the only suggestion which didn't depend on non-commodity-class hardware. Subsequently nobody would put their reputation on the line to argue definitively for or against it. Anyone care to make a stand for or against. If so, how about a mention as to a possible implementation?

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  • The Immerman-Szelepcsenyi Theorem

    - by Daniel Lorch
    In the Immerman-Szelepcsenyi Theorem, two algorithms are specified that use non-determinisim. There is a rather lengthy algorithm using "inductive counting", which determines the number of reachable configurations for a given non-deterministic turing machine. The algorithm looks like this: Let m_{i+1}=0 For all configurations C Let b=0, r=0 For all configurations D Guess a path from I to D in at most i steps If found Let r=r+1 If D=C or D goes to C in 1 step Let b=1 If r<m_i halt and reject Let m_{i+1}=m_{i+1}+b I is the starting configuration. m_i is the number of configurations reachable from the starting configuration in i steps. This algorithm only calculates the "next step", i.e. m_i+1 from m_i. This seems pretty reasonable, but since we have nondeterminisim, why don't we just write: Let m_i = 0 For all configurations C Guess a path from I to C in at most i steps If found m_i = m_i + 1 What is wrong with this algorithm? I am using nondeterminism to guess a path from I to C, and I verify reachability I am iterating through the list of ALL configurations, so I am sure to not miss any configuration I respect space bounds I can generate a certificate (the list of reachable configs) I believe I have a misunderstanding of the "power" of non-determinisim, but I can't figure out where to look next. I am stuck on this for quite a while and I would really appreciate any help.

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  • Caching Authentication Data

    - by PartlyCloudy
    Hi, I'm currently implementing a REST web service using CouchDB and RESTlet. The RESTlet layer is mainly for authentication and some minor filtering of the JSON data served by CouchDB: Clients <= HTTP = [ RESTlet <= HTTP = CouchDB ] I'm using CouchDB also to store user login data, because I don't want to add an additional database server for that purpose. Thus, each request to my service causes two CouchDB requests conducted by RESTlet (auth data + "real" request). In order to keep the service as efficent as possible, I want to reduce the number of requests, in this case redundant requests for login data. My idea now is to provide a cache (i.e.LRU-Cache via LinkedHashMap) within my RESTlet application that caches login data, because HTTP caching will probabily not be enough. But how do I invalidate the cache data, once a user changes the password, for instance. Thanks to REST, the application might run on several servers in parallel, and I don't want to create a central instance just to cache login data. Currently, I save requested auth data in the cache and try to auth new requests by using them. If a authentication fails or there is now entry available, I'll dispatch a GET request to my CouchDB storage in order to obtain the actual auth data. So in a worst case, users that have changed their data will perhaps still be able to login with their old credentials. How can I deal with that? Or what is a good strategy to keep the cache(s) up-to-date in general? Thanks in advance.

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  • Are mathematical Algorithms protected by copyright?

    - by analogy
    I wish to implement an algorithm which i read in a journal paper in my software (commercial). I want to know if this is allowed or not. The algorithm in question is described in http://arxiv.org/abs/0709.2938 It is a very simple algorithm and a number of implementations exist in python (http://igraph.sourceforge.net/) and java. One of them is in gpl another which i got from a different researcher and had no license attached. There are significant differences in two implementations, e.g. second one uses threads and multiple cores. It is possible to rewrite/ (not translate) the algorithm. So can I use it in my software or on a server for commercial purpose. Thanks UPDATE: I am completely aware of copyright on the text of paper, it was published in phys rev E. I am concerned with use of the algorithm, in commercial software. Also the publication means that unless the patent has been already filed. The method has been disclosed publicly hence barring patent in future. Also the GPL implementation is not by authors themselves but comes from a third party. Finally i am not using the GPL implementation but creating my own using C++.

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  • How do I create a good evaluation function for a new board game?

    - by A. Rex
    I write programs to play board game variants sometimes. The basic strategy is standard alpha-beta pruning or similar searches, sometimes augmented by the usual approaches to endgames or openings. I've mostly played around with chess variants, so when it comes time to pick my evaluation function, I use a basic chess evaluation function. However, now I am writing a program to play a completely new board game. How do I choose a good or even decent evaluation function? The main challenges are that the same pieces are always on the board, so a usual material function won't change based on position, and the game has been played less than a thousand times or so, so humans don't necessarily play it enough well yet to give insight. (PS. I considered a MoGo approach, but random games aren't likely to terminate.) Any ideas? Game details: The game is played on a 10-by-10 board with a fixed six pieces per side. The pieces have certain movement rules, and interact in certain ways, but no piece is ever captured. The goal of the game is to have enough of your pieces in certain special squares on the board. The goal of the computer program is to provide a player which is competitive with or better than current human players.

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  • AIR: sync gui with data-base?

    - by John Isaacks
    I am going to be building an AIR application that shows a list (about 1-25 rows of data) from a data-base. The data-base is on the web. I want the list to be as accurate as possible, meaning as soon as the data-base data changes, the list displayed in the app should update asap. I do not know of anyway that the air application could be notified when there is a change, I am thinking I am going to have to poll the data-base at certain intervals to keep an up to date list. So my question is, first is there any way to NOT have to keep checking the data-base? or if I do keep have to keep checking the data-base what is a reasonable interval to do that at? Thanks.

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  • A two way minimum spanning tree of a directed graph

    - by mvid
    Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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  • Languages and VMs: Features that are hard to optimize and why

    - by mrjoltcola
    I'm doing a survey of features in preparation for a research project. Name a mainstream language or language feature that is hard to optimize, and why the feature is or isn't worth the price paid, or instead, just debunk my theories below with anecdotal evidence. Before anyone flags this as subjective, I am asking for specific examples of languages or features, and ideas for optimization of these features, or important features that I haven't considered. Also, any references to implementations that prove my theories right or wrong. Top on my list of hard to optimize features and my theories (some of my theories are untested and are based on thought experiments): 1) Runtime method overloading (aka multi-method dispatch or signature based dispatch). Is it hard to optimize when combined with features that allow runtime recompilation or method addition. Or is it just hard, anyway? Call site caching is a common optimization for many runtime systems, but multi-methods add additional complexity as well as making it less practical to inline methods. 2) Type morphing / variants (aka value based typing as opposed to variable based) Traditional optimizations simply cannot be applied when you don't know if the type of someting can change in a basic block. Combined with multi-methods, inlining must be done carefully if at all, and probably only for a given threshold of size of the callee. ie. it is easy to consider inlining simple property fetches (getters / setters) but inlining complex methods may result in code bloat. The other issue is I cannot just assign a variant to a register and JIT it to the native instructions because I have to carry around the type info, or every variable needs 2 registers instead of 1. On IA-32 this is inconvenient, even if improved with x64's extra registers. This is probably my favorite feature of dynamic languages, as it simplifies so many things from the programmer's perspective. 3) First class continuations - There are multiple ways to implement them, and I have done so in both of the most common approaches, one being stack copying and the other as implementing the runtime to use continuation passing style, cactus stacks, copy-on-write stack frames, and garbage collection. First class continuations have resource management issues, ie. we must save everything, in case the continuation is resumed, and I'm not aware if any languages support leaving a continuation with "intent" (ie. "I am not coming back here, so you may discard this copy of the world"). Having programmed in the threading model and the contination model, I know both can accomplish the same thing, but continuations' elegance imposes considerable complexity on the runtime and also may affect cache efficienty (locality of stack changes more with use of continuations and co-routines). The other issue is they just don't map to hardware. Optimizing continuations is optimizing for the less-common case, and as we know, the common case should be fast, and the less-common cases should be correct. 4) Pointer arithmetic and ability to mask pointers (storing in integers, etc.) Had to throw this in, but I could actually live without this quite easily. My feelings are that many of the high-level features, particularly in dynamic languages just don't map to hardware. Microprocessor implementations have billions of dollars of research behind the optimizations on the chip, yet the choice of language feature(s) may marginalize many of these features (features like caching, aliasing top of stack to register, instruction parallelism, return address buffers, loop buffers and branch prediction). Macro-applications of micro-features don't necessarily pan out like some developers like to think, and implementing many languages in a VM ends up mapping native ops into function calls (ie. the more dynamic a language is the more we must lookup/cache at runtime, nothing can be assumed, so our instruction mix is made up of a higher percentage of non-local branching than traditional, statically compiled code) and the only thing we can really JIT well is expression evaluation of non-dynamic types and operations on constant or immediate types. It is my gut feeling that bytecode virtual machines and JIT cores are perhaps not always justified for certain languages because of this. I welcome your answers.

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  • Indentation control while developing a small python like language

    - by sap
    Hello, I'm developing a small python like language using flex, byacc (for lexical and parsing) and C++, but i have a few questions regarding scope control. just as python it uses white spaces (or tabs) for indentation, not only that but i want to implement index breaking like for instance if you type "break 2" inside a while loop that's inside another while loop it would not only break from the last one but from the first loop as well (hence the number 2 after break) and so on. example: while 1 while 1 break 2 'hello world'!! #will never reach this. "!!" outputs with a newline end 'hello world again'!! #also will never reach this. again "!!" used for cout end #after break 2 it would jump right here but since I don't have an "anti" tab character to check when a scope ends (like C for example i would just use the '}' char) i was wondering if this method would the the best: I would define a global variable, like "int tabIndex" on my yacc file that i would access in my lex file using extern. then every time i find a tab character on my lex file i would increment that variable by 1. when parsing on my yacc file if i find a "break" keyword i would decrement by the amount typed after it from the tabIndex variable, and when i reach and EOF after compiling and i get a tabIndex != 0 i would output compilation error. now the problem is, whats the best way to see if the indentation got reduced, should i read \b (backspace) chars from lex and then reduce the tabIndex variable (when the user doesn't use break)? another method to achieve this? also just another small question, i want every executable to have its starting point on the function called start() should i hardcode this onto my yacc file? sorry for the long question any help is greatly appreciated. also if someone can provide an yacc file for python would be nice as a guideline (tried looking on Google and had no luck). thanks in advance.

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  • how to use random bits to simulate a fair 26-sided die?

    - by Michael Levin
    How do I use a random number generator that gives bits (0 or 1) to simulate a fair 26-sided die? I want to use a bitstream to pick letters of the English alphabet such that the odds of any one letter coming up is the same as the odds of any other letter (I know real words aren't like that and have specific frequency distributions for each letter but it doesn't matter here). What's the best way to use binary 0/1 decisions to pick letters fairly from the set A-Z? I can think of a few ways to map bits onto letters but it's not obvious to me that they won't be biased. Is there a known good way?

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  • Searching through large data set

    - by calccrypto
    how would i search through a list with ~5 mil 128bit (or 256, depending on how you look at it) strings quickly and find the duplicates (in python)? i can turn the strings into numbers, but i don't think that's going to help much. since i haven't learned much information theory, is there anything about this in information theory? and since these are hashes already, there's no point in hashing them again

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  • Can Goldberg algorithm in ocamlgraph be used to find Minimum Cost Flow graph?

    - by Tautrimas
    I'm looking for an implementation to the Minimum Cost Flow graph problem in OCaml. OCaml library ocamlgraph has Goldberg algorithm implementation. The paper called Efficient implementation of the Goldberg-Tarjan minimum-cost flow algorithm is noting that Goldberg-Tarjan algorithm can find minimum cost graph. Question is, does ocamlgraph algorithm also find the minimum cost? Library documentation only states, that it's suitable at least for the maximum flow problem. If not, does anybody have a good link to a nice any minimum cost optimization algorithm code? I will manually translate it into OCaml then. Forgive me, if I missed it on Wikipedia: there are too many algos on flow networks for the first day!

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  • changing user in ubuntu

    - by Rahul Mehta
    Hi , this is my ls -all, the zfapi folder have the root right , how can i change this to www-data. Also Please advise what is the first root and secont root is ? Thanks drwxr-xr-x 4 www-data www-data 4096 2011-01-06 18:21 cdnapi -rw-r--r-- 1 www-data www-data 678 2010-08-30 12:02 config.js drwxr-xr-x 4 www-data www-data 4096 2010-11-23 15:55 css drwxr-xr-x 7 www-data www-data 4096 2010-11-17 13:12 images -rw-r--r-- 1 www-data www-data 25064 2010-12-17 18:26 index.html -rw-r--r-- 1 www-data www-data 19830 2010-12-18 11:24 init.js drwxr-xr-x 2 www-data www-data 4096 2010-12-02 12:34 lib -rw-r--r-- 1 www-data www-data 18758 2010-12-06 18:00 styles.css -rw-r--r-- 1 www-data www-data 1081 2010-10-21 17:56 testbganim.html drwxr-xr-x 2 www-data www-data 4096 2010-12-17 11:15 yapi drwxr-xr-x 7 root root 4096 2011-01-07 18:20 zfapi

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  • HLSL How can one pass data between shaders / read existing colour value?

    - by RJFalconer
    Hello all, I have 2 HLSL ps2.0 shaders. Simplified, they are: Shader 1 Reads texture Outputs colour value based on this texture Shader 2 Needs to read in existing colour (or have it passed in/read from a register) Outputs the final colour which is a function of the previous colour (They need to be different shaders as I've reached the maximum vertex-shader outputs for 1 shader) My problem is I cannot work out how Shader 2 can access the existing fragment/pixel colour. Is the only way for shaders to interact really just the alpha blending options? These aren't sufficient if I want to use the colour as input to my function.

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  • Use queried json data in a function

    - by SztupY
    I have a code similar to this: $.ajax({ success: function(data) { text = ''; for (var i = 0; i< data.length; i++) { text = text + '<a href="#" id="Data_'+ i +'">' + data[i].Name + "</a><br />"; } $("#SomeId").html(text); for (var i = 0; i< data.length; i++) { $("#Data_"+i).click(function() { alert(data[i]); RunFunction(data[i]); return false; }); } } }); This gets an array of some data in json format, then iterates through this array generating a link for each entry. Now I want to add a function for each link that will run a function that does something with this data. The problem is that the data seems to be unavailable after the ajax success function is called (although I thought that they behave like closures). What is the best way to use the queried json data later on? (I think setting it as a global variable would do the job, but I want to avoid that, mainly because this ajax request might be called multiple times) Thanks.

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  • Subgraph isomorphism on disconnected graphs with connection rules

    - by Mac
    Hello I was wondering if anyone knows about a solution to the following problem: Given a graph g as query and a set of graphs B with connection rules R. The connection rules describe how two graphs out of B can be linked together. Linking points are marked vertexes. Find all combination of graphs in B that contain g as a subgraph. Regards Mac

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  • How do I display data in a table and allow users to copy selected data?

    - by cfouche
    Hi I have a long list of data that I want to display in table format to users. The data changes when the user performs certain actions in my app, but it is not directly editable. So the user can create a reasonably big table of data, but he can't change individual cells' values. However, I do want the data to be copy-able. So I want it to be possible for the user to select some or all of the cells, and do a ctrl-C to copy the data to his clipboard, and then a ctrl-V to paste the data to an external text editor. At the moment, I'm displaying the data in a ListView with a GridView and this works perfectly, except that GridView doesn't allow one to copy data. What other options can I try? Ours is a WPF app, coding in c#.

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  • How to use a data type (table) defined in another database in SQL2k8?

    - by Victor Rodrigues
    I have a Table Type defined in a database. It is used as a table-valued parameter in a stored procedure. I would like to call this procedure from another database, and in order to pass the parameter, I need to reference this defined type. But when I do DECLARE @table dbOtherDatabase.dbo.TypeName , it tells me that The type name 'dbOtherDatabase.dbo.TypeName' contains more than the maximum number of prefixes. The maximum is 1. How could I reference this table type?

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  • After adding data files to a file group Is there a way to distribute the data into the new files?

    - by Blootac
    I have a database in a single file group, with a single file group. I've added 7 data files to this file group. Is there a way to rebalance the data over the 8 data files other than by telling sql server to empty the original? If this is the only way, is it possible to allow sql server to start writing to this file? MSDN says that once its empty its marked so no new data will be written to it. What I'm aiming for is 8 equally balanced data files. I'm running SQL Server 2005 standard edition. Thanks

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