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• Javascript: Machine Constants Applicable?

  - by DavidB2013

  I write numerical routines for students of science and engineering (although they are freely available for use by anybody else as well) and am wondering how to properly use machine constants in a JavaScript program, or if they are even applicable. For example, say I am writing a program in C++ that numerically computes the roots of the following equation: exp(-0.7x) + sin(3x) - 1.2x + 0.3546 = 0 A root-finding routine should be able to compute roots to within the machine epsilon. In C++, this value is specified by the language: DBL_EPSILON. C++ also specifies the smallest and largest values that can be held by a float or double variable. However, how does this convert to JavaScript? Since a Javascript program runs in a web browser, and I don't know what kind of computer will run the program, and JavaScript does not have corresponding predefined values for these quantities, how can I implement my own version of these constants so that my programs compute results to as much accuracy as allowed on the computer running the web browser? My first draft is to simply copy over the literal constants from C++: FLT_MIN: 1.17549435082229e-038 FLT_MAX: 3.40282346638529e+038 DBL_EPSILON: 2.2204460492503131e-16 I am also willing to write small code blocks that could compute these values for each machine on which the program is run. That way, a supercomputer might compute results to a higher accuracy than an old, low-level, PC. BUT, I don't know if such a routine would actually reach the computer, in which case, I would be wasting my time. Anybody here know how to compute and use (in Javascript) values that correspond to machine constants in a compiled language? Is it worth my time to write small programs in Javascript that compute DBL_EPSILON, FLT_MIN, FLT_MIN, etc. for use in numerical routines? Or am I better off simply assigning literal constants that come straight from C++ on a standard Windows PC?

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• Better to build or buy a compute grid platform?

  - by James B

  I am looking to do some quite processor-intensive brute force processing for string matching. I have run my prototype in a multi-threaded environment and compared the performance to an implementation using Gridgain with a couple of nodes (also multithreaded). The performance I observed was that my Gridgain implementation performed slower to my multithreaded implementation. It could be the case that there was a flaw in my gridgain implementation, but it was only a prototype, and I thought the results were indicative. So my question is this: What are the advantages of having to learn and then build an implementation for a particular grid platform (hadoop, gridgain, or EC2 if going hosted - other suggestions welcome), when one could fairly easily put together a lightweight compute grid platform with a much shallower learning curve?...i.e. what do we get for free with these cloud/grid platforms that are worth having/tricky to implement? (Please note, I don't have any need for a data grid) Cheers, -James (p.s. Happy to make this community wiki if needbe)

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• Java or Python distributed compute job (on a student budget)?

  - by midget_sadhu

  I have a large dataset (c. 40G) that I want to use for some NLP (largely embarrassingly parallel) over a couple of computers in the lab, to which i do not have root access, and only 1G of user space. I experimented with hadoop, but of course this was dead in the water-- the data is stored on an external usb hard drive, and i cant load it on to the dfs because of the 1G user space cap. I have been looking into a couple of python based options (as I'd rather use NLTK instead of Java's lingpipe if I can help it), and it seems distributed compute options look like: Ipython DISCO After my hadoop experience, i am trying to make sure i try and make an informed choice -- any help on what might be more appropriate would be greatly appreciated. Amazon's EC2 etc not really an option, as i have next to no budget.

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• How can I compute the average cost for this solution of the element uniqueness problem?

  - by Alceu Costa

  In the book Introduction to the Design & Analysis of Algorithms, the following solution is proposed to the element uniqueness problem: ALGORITHM UniqueElements(A[0 .. n-1]) // Determines whether all the elements in a given array are distinct // Input: An array A[0 .. n-1] // Output: Returns "true" if all the elements in A are distinct // and false otherwise. for i := 0 to n - 2 do for j := i + 1 to n - 1 do if A[i] = A[j] return false return true How can I compute the average cost (i.e. number of comparisons for a given n) for this algorithm? What is a reasonable assumption about the input?

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• What algorithms compute directions from point A to point B on a map?

  - by A. Rex

  How do map providers (such as Google or Yahoo! Maps) suggest directions? I mean, they probably have real-world data in some form, certainly including distances but also perhaps things like driving speeds, presence of sidewalks, train schedules, etc. But suppose the data were in a simpler format, say a very large directed graph with edge weights reflecting distances. I want to be able to quickly compute directions from one arbitrary point to another. Sometimes these points will be close together (within one city) while sometimes they will be far apart (cross-country). Graph algorithms like Dijkstra's algorithm will not work because the graph is enormous. Luckily, heuristic algorithms like A* will probably work. However, our data is very structured, and perhaps some kind of tiered approach might work? (For example, store precomputed directions between certain "key" points far apart, as well as some local directions. Then directions for two far-away points will involve local directions to a key points, global directions to another key point, and then local directions again.) What algorithms are actually used in practice? PS. This question was motivated by finding quirks in online mapping directions. Contrary to the triangle inequality, sometimes Google Maps thinks that X-Z takes longer and is farther than using an intermediate point as in X-Y-Z. But maybe their walking directions optimize for another parameter, too? PPS. Here's another violation of the triangle inequality that suggests (to me) that they use some kind of tiered approach: X-Z versus X-Y-Z. The former seems to use prominent Boulevard de Sebastopol even though it's slightly out of the way. (Edit: this example doesn't work anymore, but did at the time of the original post. The one above still works as of early November 2009.)

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• Amazon Elastic Compute Cloud: how to set up a small and persistent test machine?

  - by mjustin

  Hello, is there a short tutorial available which shows how I can set up a small Linux server on Amazon EC2 so that I can configure it and launch it when needed? I understand that there is EBS to provide a persistent storage and that an image can be booted right from EBS. There are also existing images which are perfect starting points, with Linux installed, so I simply have to 'copy' somehow an existing image to EBS, and configure it there. Is there some article which guides through these steps?

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• Any reviews about the Amazon Elastic Compute Cloud (Amazon EC2)?

  - by hkshambesh

  I want to use it for hosting large system which will contain x-large database.

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• Windows Azure VMs - New "Stopped" VM Options Provide Cost-effective Flexibility for On-Demand Workloads

  - by KeithMayer

  Originally posted on: http://geekswithblogs.net/KeithMayer/archive/2013/06/22/windows-azure-vms---new-stopped-vm-options-provide-cost-effective.aspxDidn’t make it to TechEd this year? Don’t worry!  This month, we’ll be releasing a new article series that highlights the Best of TechEd announcements and technical information for IT Pros.  Today’s article focuses on a new, much-heralded enhancement to Windows Azure Infrastructure Services to make it more cost-effective for spinning VMs up and down on-demand on the Windows Azure cloud platform. NEW! VMs that are shutdown from the Windows Azure Management Portal will no longer continue to accumulate compute charges while stopped! Previous to this enhancement being available, the Azure platform maintained fabric resource reservations for VMs, even in a shutdown state, to ensure consistent resource availability when starting those VMs in the future.  And, this meant that VMs had to be exported and completely deprovisioned when not in use to avoid compute charges. In this article, I'll provide more details on the scenarios that this enhancement best fits, and I'll also review the new options and considerations that we now have for performing safe shutdowns of Windows Azure VMs. Which scenarios does the new enhancement best fit? Being able to easily shutdown VMs from the Windows Azure Management Portal without continued compute charges is a great enhancement for certain cloud use cases, such as: On-demand dev/test/lab environments - Freely start and stop lab VMs so that they are only accumulating compute charges when being actively used.  "Bursting" load-balanced web applications - Provision a number of load-balanced VMs, but keep the minimum number of VMs running to support "normal" loads. Easily start-up the remaining VMs only when needed to support peak loads. Disaster Recovery - Start-up "cold" VMs when needed to recover from disaster scenarios. BUT ... there is a consideration to keep in mind when using the Windows Azure Management Portal to shutdown VMs: although performing a VM shutdown via the Windows Azure Management Portal causes that VM to no longer accumulate compute charges, it also deallocates the VM from fabric resources to which it was previously assigned.  These fabric resources include compute resources such as virtual CPU cores and memory, as well as network resources, such as IP addresses.  This means that when the VM is later started after being shutdown from the portal, the VM could be assigned a different IP address or placed on a different compute node within the fabric. In some cases, you may want to shutdown VMs using the old approach, where fabric resource assignments are maintained while the VM is in a shutdown state.  Specifically, you may wish to do this when temporarily shutting down or restarting a "7x24" VM as part of a maintenance activity.  Good news - you can still revert back to the old VM shutdown behavior when necessary by using the alternate VM shutdown approaches listed below.  Let's walk through each approach for performing a VM Shutdown action on Windows Azure so that we can understand the benefits and considerations of each... How many ways can I shutdown a VM? In Windows Azure Infrastructure Services, there's three general ways that can be used to safely shutdown VMs: Shutdown VM via Windows Azure Management Portal Shutdown Guest Operating System inside the VM Stop VM via Windows PowerShell using Windows Azure PowerShell Module Although each of these options performs a safe shutdown of the guest operation system and the VM itself, each option handles the VM shutdown end state differently. Shutdown VM via Windows Azure Management Portal When clicking the Shutdown button at the bottom of the Virtual Machines page in the Windows Azure Management Portal, the VM is safely shutdown and "deallocated" from fabric resources.  Shutdown button on Virtual Machines page in Windows Azure Management Portal  When the shutdown process completes, the VM will be shown on the Virtual Machines page with a "Stopped ( Deallocated )" status as shown in the figure below. Virtual Machine in a "Stopped (Deallocated)" Status "Deallocated" means that the VM configuration is no longer being actively associated with fabric resources, such as virtual CPUs, memory and networks. In this state, the VM will not continue to allocate compute charges, but since fabric resources are deallocated, the VM could receive a different internal IP address ( called "Dynamic IPs" or "DIPs" in Windows Azure ) the next time it is started.  TIP: If you are leveraging this shutdown option and consistency of DIPs is important to applications running inside your VMs, you should consider using virtual networks with your VMs.  Virtual networks permit you to assign a specific IP Address Space for use with VMs that are assigned to that virtual network.  As long as you start VMs in the same order in which they were originally provisioned, each VM should be reassigned the same DIP that it was previously using. What about consistency of External IP Addresses? Great question! External IP addresses ( called "Virtual IPs" or "VIPs" in Windows Azure ) are associated with the cloud service in which one or more Windows Azure VMs are running.  As long as at least 1 VM inside a cloud service remains in a "Running" state, the VIP assigned to a cloud service will be preserved.  If all VMs inside a cloud service are in a "Stopped ( Deallocated )" status, then the cloud service may receive a different VIP when VMs are next restarted. TIP: If consistency of VIPs is important for the cloud services in which you are running VMs, consider keeping one VM inside each cloud service in the alternate VM shutdown state listed below to preserve the VIP associated with the cloud service. Shutdown Guest Operating System inside the VM When performing a Guest OS shutdown or restart ( ie., a shutdown or restart operation initiated from the Guest OS running inside the VM ), the VM configuration will not be deallocated from fabric resources. In the figure below, the VM has been shutdown from within the Guest OS and is shown with a "Stopped" VM status rather than the "Stopped ( Deallocated )" VM status that was shown in the previous figure. Note that it may require a few minutes for the Windows Azure Management Portal to reflect that the VM is in a "Stopped" state in this scenario, because we are performing an OS shutdown inside the VM rather than through an Azure management endpoint. Virtual Machine in a "Stopped" Status VMs shown in a "Stopped" status will continue to accumulate compute charges, because fabric resources are still being reserved for these VMs.  However, this also means that DIPs and VIPs are preserved for VMs in this state, so you don't have to worry about VMs and cloud services getting different IP addresses when they are started in the future. Stop VM via Windows PowerShell In the latest version of the Windows Azure PowerShell Module, a new -StayProvisioned parameter has been added to the Stop-AzureVM cmdlet. This new parameter provides the flexibility to choose the VM configuration end result when stopping VMs using PowerShell: When running the Stop-AzureVM cmdlet without the -StayProvisioned parameter specified, the VM will be safely stopped and deallocated; that is, the VM will be left in a "Stopped ( Deallocated )" status just like the end result when a VM Shutdown operation is performed via the Windows Azure Management Portal.  When running the Stop-AzureVM cmdlet with the -StayProvisioned parameter specified, the VM will be safely stopped but fabric resource reservations will be preserved; that is the VM will be left in a "Stopped" status just like the end result when performing a Guest OS shutdown operation. So, with PowerShell, you can choose how Windows Azure should handle VM configuration and fabric resource reservations when stopping VMs on a case-by-case basis. TIP: It's important to note that the -StayProvisioned parameter is only available in the latest version of the Windows Azure PowerShell Module.  So, if you've previously downloaded this module, be sure to download and install the latest version to get this new functionality. Want to Learn More about Windows Azure Infrastructure Services? To learn more about Windows Azure Infrastructure Services, be sure to check-out these additional FREE resources: Become our next "Early Expert"! Complete the Early Experts "Cloud Quest" and build a multi-VM lab network in the cloud for FREE!  Build some cool scenarios! Check out our list of over 20+ Step-by-Step Lab Guides based on key scenarios that IT Pros are implementing on Windows Azure Infrastructure Services TODAY!  Looking forward to seeing you in the Cloud! - Keith Build Your Lab! Download Windows Server 2012 Don’t Have a Lab? Build Your Lab in the Cloud with Windows Azure Virtual Machines Want to Get Certified? Join our Windows Server 2012 "Early Experts" Study Group

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• Presentations on OVCA & OVN

  - by uwes

  The following three presentations regarding Oracle Virtual Compute Appliance and Oracle SDN from Oracle Open World sessions are now available for download from eSTEP portal. Oracle Virtual Compute Appliance: From Power On to Production in About an Hour Charlie Boyle and Premal Savla give an overview of the Oracle Virtual Compute Appliance. This presentation is a mix of the business and technical slides. Rapid Application Deployment with Oracle Virtual Compute Appliance Kurt Hackel and Saar Maoz, both in Product Development, explain how to use Oracle VM templates to deploy applications faster and walk through a demo with Oracle VM templates for Oracle Database.  Oracle SDN: Software-Defined Networking in a Hybrid, Open Data Center Krishna Srinivasan and Ronen Kofman explain Oracle SDN and provide use cases for multi-tenant private cloud, IaaS, serving Tier 1 application and virtual network services. The presentation can be downloaded from eSTEP portal. URL: http://launch.oracle.com/ PIN: eSTEP_2011 The material can be found under tab eSTEP Download Located under: Recent Updates and Engineered Sysytems/Optimized Solutions

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• Graph Theory: How to compute closeness centrality for each node in a set of data?

  - by Jordan

  I'd like to learn how to apply network theory to my own cache of relational data. I'm trying to build a demo of a new way of browsing a music library, using network theory, that I think would make for a very intuitive and useful way of finding the right song at any given time. I have all the data (artists as nodes, similarity from 0 to 1 between each artist and those it is related to) and I can already program, but I don't know how to actually calculate the centrality of a node from that. I've spent a while trying to email different professors at my school but no one seems to know where I can learn this. I hope someone's done something similar. Thanks in advance you guys! ~Jordan

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• In C# should I reuse a function / property parameter to compute temp result or create a temporary v

  - by Hamish Grubijan

  The example below may not be problematic as is, but it should be enough to illustrate a point. Imagine that there is a lot more work than trimming going on. public string Thingy { set { // I guess we can throw a null reference exception here on null. value = value.Trim(); // Well, imagine that there is so much processing to do this.thingy = value; // That this.thingy = value.Trim() would not fit on one line ... So, if the assignment has to take two lines, then I either have to abusereuse the parameter, or create a temporary variable. I am not a big fan of temporary variables. On the other hand, I am not a fan of convoluted code. I did not include an example where a function is involved, but I am sure you can imagine it. One concern I have is if a function accepted a string and the parameter was "abused", and then someone changed the signature to ref in both places - this ought to mess things up, but ... who would knowingly make such a change if it already worked without a ref? Seems like it is their responsibility in this case. If I mess with the value of value, am I doing something non-trivial under the hood? If you think that both approaches are acceptable, then which do you prefer and why? Thanks.

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• How to compute the probability of a multi-class prediction using libsvm?

  - by Cuga

  I'm using libsvm and the documentation leads me to believe that there's a way to output the believed probability of an output classification's accuracy. Is this so? And if so, can anyone provide a clear example of how to do it in code? Currently, I'm using the Java libraries in the following manner SvmModel model = Svm.svm_train(problem, parameters); SvmNode x[] = getAnArrayOfSvmNodesForProblem(); double predictedValue = Svm.svm_predict(model, x);

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• How do I compute the approximate entropy of a bit string?

  - by dreeves

  Is there a standard way to do this? Googling -- "approximate entropy" bits -- uncovers multiple academic papers but I'd like to just find a chunk of pseudocode defining the approximate entropy for a given bit string of arbitrary length. (In case this is easier said than done and it depends on the application, my application involves 16,320 bits of encrypted data (cyphertext). But encrypted as a puzzle and not meant to be impossible to crack. I thought I'd first check the entropy but couldn't easily find a good definition of such. So it seemed like a question that ought to be on StackOverflow! Ideas for where to begin with de-cyphering 16k random-seeming bits are also welcome...) See also this related question: http://stackoverflow.com/questions/510412/what-is-the-computer-science-definition-of-entropy

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• MySQL: Is it possible to compute MAX( AVG (field) )?

  - by Brad

  My current query reads: SELECT entry_id, user_id, cat_id, AVG( rating ) as avg_rate FROM entry_rate WHERE 1 GROUP BY entry_id cat_id relates to different categories: 1, 2, 3 or 4 Is there a way I can find the maximum average for each user in each category without setting up an additional table? The return could potentially be 4 maximum avg_rate for each user_id Visit the link below for example: http://lh5.ggpht.com/_rvDQuhTddnc/S8Os_77qR9I/AAAAAAAAA2M/IPmzNeYjfCA/s800/table1.jpg

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• In APL, how can I compute the lowest unused positive integer from a given set of integers?

  - by Paul Mansour

  For example, given 1 8 4 9 0 2 , return 3. Thanks.

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• Need .Net method to compute a Google Pagerank request checksum.

  - by Steve K

  The company I work for is currently developing a SEO tool which needs to include a domain or url Pagerank. It is possible to retrieve such data directly from Google by sending a request to the url called by the Google ToolBar. On of the parameters send to that url is a checksum of the domain whose pagerank is being requested. I have found multiple .Net methods for calculating that check sum; however, every one randomly returns corrupt values every so often. I can only handle errors to a certain point before my final data set becomes useless. I know that there are countless tools out there, from browser plugins to desktop applications, that can process page rank, so it can't be impossible. My question, then, is two fold: 1) Any anyone heard of the problem I am having? (specifically in .Net) If so, how can it (or has it) be resolved? 2) Is there a better source for retrieving Pagerank data? Below is the Url and checksum code I have been using. "http://toolbarqueries.google.com/search?client=navclient-auto&ie=UTF-8&oe=UTF-8&features=Rank:&q=info:" & strUrl & "ch=" & strCheckSum where: strUrl = the url being queried strCheckSum = CheckHash(GetHash(url)) (see code below) Any help would be greatly appreciated. ''' <summary> ''' Returns a hash-string from the site's URL ''' </summary> ''' <param name="_SiteURL">full URL as indexed by Google</param> ''' <returns>HASH for site as a string</returns> Private Shared Function GetHash(ByVal _SiteURL As String) As String Try Dim _Check1 As Long = StrToNum(_SiteURL, 5381, 33) Dim _Check2 As Long = StrToNum(_SiteURL, 0, 65599) _Check1 >>= 2 _Check1 = ((_Check1 >> 4) And 67108800) Or (_Check1 And 63) _Check1 = ((_Check1 >> 4) And 4193280) Or (_Check1 And 1023) _Check1 = ((_Check1 >> 4) And 245760) Or (_Check1 And 16383) Dim T1 As Long = ((((_Check1 And 960) << 4) Or (_Check1 And 60)) << 2) Or (_Check2 And 3855) Dim T2 As Long = ((((_Check1 And 4294950912) << 4) Or (_Check1 And 15360)) << 10) Or (_Check2 And 252641280) Return Convert.ToString(T1 Or T2) Catch Return "0" End Try End Function ''' <summary> ''' Checks the HASH-string returned and adds check numbers as necessary ''' </summary> ''' <param name="_HashNum">generated HASH-string</param> ''' <returns>modified HASH-string</returns> Private Shared Function CheckHash(ByVal _HashNum As String) As String Try Dim _CheckByte As Long = 0 Dim _Flag As Long = 0 Dim _tempI As Long = Convert.ToInt64(_HashNum) If _tempI < 0 Then _tempI = _tempI * (-1) End If Dim _Hash As String = _tempI.ToString() Dim _Length As Integer = _Hash.Length For x As Integer = _Length - 1 To 0 Step -1 Dim _quick As Char = _Hash(x) Dim _Re As Long = Convert.ToInt64(_quick.ToString()) If 1 = (_Flag Mod 2) Then _Re += _Re _Re = CLng(((_Re \ 10) + (_Re Mod 10))) End If _CheckByte += _Re _Flag += 1 Next _CheckByte = _CheckByte Mod 10 If 0 <> _CheckByte Then _CheckByte = 10 - _CheckByte If 1 = (_Flag Mod 2) Then If 1 = (_CheckByte Mod 2) Then _CheckByte >>= 1 End If End If End If If _Hash.Length = 9 Then _CheckByte += 5 End If Return "7" + _CheckByte.ToString() + _Hash Catch Return "0" End Try End Function ''' <summary> ''' Converts the string (site URL) into numbers for the HASH ''' </summary> ''' <param name="_str">Site URL as passed by GetHash()</param> ''' <param name="_Chk">Necessary passed value</param> ''' <param name="_Magic">Necessary passed value</param> ''' <returns>Long Integer manipulation of string passed</returns> Private Shared Function StrToNum(ByVal _str As String, ByVal _Chk As Long, ByVal _Magic As Long) As Long Try Dim _Int64Unit As Long = Convert.ToInt64(Math.Pow(2, 32)) Dim _StrLen As Integer = _str.Length For x As Integer = 0 To _StrLen - 1 _Chk *= _Magic If _Chk >= _Int64Unit Then _Chk = (_Chk - (_Int64Unit * Convert.ToInt64(_Chk \ _Int64Unit))) _Chk = IIf((_Chk < -2147483648), (_Chk + _Int64Unit), _Chk) End If _Chk += CLng(Asc(_str(x))) Next Catch End Try Return _Chk End Function

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• How to compute a unicode string which bidirectional representation is specified?

  - by valdo

  Hello, fellows. I have a rather pervert question. Please forgive me :) There's an official algorithm that describes how bidirectional unicode text should be presented. http://www.unicode.org/reports/tr9/tr9-15.html I receive a string (from some 3rd-party source), which contains latin/hebrew characters, as well as digits, white-spaces, punctuation symbols and etc. The problem is that the string that I receive is already in the representation form. I.e. - the sequence of characters that I receive should just be presented from left to right. Now, my goal is to find the unicode string which representation is exactly the same. Means - I need to pass that string to another entity; it would then render this string according to the official algorithm, and the result should be the same. Assuming the following: The default text direction (of the rendering entity) is RTL. I don't want to inject "special unicode characters" that explicitly override the text direction (such as RLO, RLE, etc.) I suspect there may exist several solutions. If so - I'd like to preserve the RTL-looking of the string as much as possible. The string usually consists of hebrew words mostly. I'd like to preserve the correct order of those words, and characters inside those words. Whereas other character sequences may (and should) be transposed. One naive way to solve this is just to swap the whole string (this takes care of the hebrew words), and then swap inside it sequences of non-hebrew characters. This however doesn't always produce correct results, because actual rules of representation are rather complex. The only comprehensive algorithm that I see so far is brute-force check. The string can be divided into sequences of same-class characters. Those sequences may be joined in random order, plus any of them may be reversed. I can check all those combinations to obtain the correct result. Plus this technique may be optimized. For instance the order of hebrew words is known, so we only have to check different combinations of their "joining" sequences. Any better ideas? If you have an idea, not necessarily the whole solution - it's ok. I'll appreciate any idea. Thanks in advance.

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• How to compute palindrome from a stream of characters in sub-linear space/time?

  - by wrick

  I don't even know if a solution exists or not. Here is the problem in detail. You are a program that is accepting an infinitely long stream of characters (for simplicity you can assume characters are either 1 or 0). At any point, I can stop the stream (let's say after N characters were passed through) and ask you if the string received so far is a palindrome or not. How can you do this using less sub-linear space and/or time.

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• Is it possible to compute the minimum of three numbers by using two comparisons at the same time?

  - by Milo Hou

  I've been trying to think up of some way that I could do two comparisons at the same time to find the greatest/least of three numbers. Arithmetic operations on them are considered "free" in this case. That is to say, the classical way of finding the greater of two, and then comparing it to the third number isn't valid in this case because one comparison depends on the result of the other. Is it possible to use two comparisons where this isn't the case? I was thinking maybe comparing the differences of the numbers somehow or their products or something, but came up with nothing. Just to reemphasize, two comparisons are still done, just that neither comparison relies on the result of the other comparison. EDIT: what about: boolA = A^2 + B^2 < C^2 boolB = A > B if boolA then max=C else if boolB then max=A else max=B

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• Can Visual Studio (should it be able to) compute a diff between any two changesets associated with a

  - by Hamish Grubijan

  Here is my use case: I start on a project XYZ, for which I create a work item, and I make frequent check-ins, easily 10-20 in total. ALL of the code changes will be code-read and code-reviewed. The change sets are not consecutive - other people check-in in-between my changes, although they are very unlikely to touch the exact same files. So ... at the en of the project I am interested in a "total diff" - as if there was a single check-in by me to complete the entire project. In theory this is computable. From the list of change sets associated with the work item, you get the list of all files that were affected. Then, the algorithm can aggregate individual diffs over each file and combine them into one. It is possible that a pure total diff is uncomputable due to the fact that someone else renamed files, or changed stuff around very closely, or in the same functions as me. I that case ... I suppose a total diff can include those changes by non-me as well, and warn me about the fact. I would find this very useful, but I do not know how to do t in practice. Can Visual Studio 2008/2010 (and/or TFS server) do it? Are there other source control systems capable of doing this? Thanks.

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• How can we compute the LAST page with JPA?

  - by Kevin

  I would like to implement pagination in my Servlet/EJB/JPA-Hibernate project, but I can't figure out how only one page from the query and know the number of pages I must display I use setFirstResult(int first) ; setMaxResults(int max) ; and that's working alright, but how can I know how many pages I will have in total? (Hibernate is my JPA provider, but I would prefer using only JPA if possible) UPDATE: COUNT() seems to be the better/easiest solution; but what can be the cost of SELECT COUNT(*) FROM ... in comparison with executeQuery("SELECT * FROM ...).getListResult().size() ?

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• In C# should I reuse a function / property parameter to compute cleaner temporary value or create a

  - by Hamish Grubijan

  The example below may not be problematic as is, but it should be enough to illustrate a point. Imagine that there is a lot more work than trimming going on. public string Thingy { set { // I guess we can throw a null reference exception here on null. value = value.Trim(); // Well, imagine that there is so much processing to do this.thingy = value; // That this.thingy = value.Trim() would not fit on one line ... So, if the assignment has to take two lines, then I either have to abusereuse the parameter, or create a temporary variable. I am not a big fan of temporary variables. On the other hand, I am not a fan of convoluted code. I did not include an example where a function is involved, but I am sure you can imagine it. One concern I have is if a function accepted a string and the parameter was "abused", and then someone changed the signature to ref in both places - this ought to mess things up, but ... who would knowingly make such a change if it already worked without a ref? Seems like it is their responsibility in this case. If I mess with the value of value, am I doing something non-trivial under the hood? If you think that both approaches are acceptable, then which do you prefer and why? Thanks.

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• Easy way to compute how close an auto_increment is to its maximum value?

  - by David M

  So yesterday we had a table that has an auto_increment PK for a smallint that reached its maximum. We had to alter the table on an emergency basis, which is definitely not how we like to roll. Is there an easy way to report on how close each auto_increment field that we use is to its maximum? The best way I can think of is to do a SHOW CREATE TABLE statement, parse out the size of the auto-incremented column, then compare that to the AUTO_INCREMENT value for the table. On the other hand, given that the schema doesn't change very often, should I store information about the columns' maximum values and get the current AUTO_INCREMENT with SHOW TABLE STATUS?

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• How do I compute a variable in Javascript if and only if it is used?

  - by LLer

  This is what I'm doing right now. var foo = function() { var x = someComplicatedComputationThatMayTakeMoreTime(); this.foo = function() { return x; }; return x; } It works but only if foo is called as a function like so foo(); But what if I want to call it as a normal variable with a value? I could modify the code to be var foo = function() { var x = someComplicatedComputationThatMayTakeMoreTime(); this.foo = x; return x; } That would allow me to only call it once as a function and after that as a regular variable. But it's still not what I want. Plus it gets complicated if it accidentally gets called as a function again, returning an error. Is this even possible in Javascript?

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• using fortran subroutine,compute the distance among (x1,y1),(x2,y2),(x3,y3).

  - by prachi

  REJKYLJJJJJJJYLJKD TRJIHPOOOOOOOOOOOOOOOOOOOOOODKH TRLKHNNNNNNNNNNNNNNNNUJRYIOSESESESESESESESESESESESESESEHGTLKH

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