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  • How to optimize Dijkstra algorithm for a single shortest path between 2 nodes?

    - by Nazgulled
    Hi, I was trying to understand this implementation in C of the Dijkstra algorithm and at the same time modify it so that only the shortest path between 2 specific nodes (source and destination) is found. However, I don't know exactly what do to. The way I see it, there's nothing much to do, I can't seem to change d[] or prev[] cause those arrays aggregate some important data for the shortest path calculation. The only thing I can think of is stopping the algorithm when the path is found, that is, break the cycle when mini = destination when it's being marked as visited. Is there anything else I could do to make it better or is that enough? P.S: I just noticed that the for loops start at 1 until <=, why can't it start at 0 and go until <?

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  • What is the algorithm used by the memberwise equality test in .NET structs?

    - by Damian Powell
    What is the algorithm used by the memberwise equality test in .NET structs? I would like to know this so that I can use it as the basis for my own algorithm. I am trying to write a recursive memberwise equality test for arbitrary objects (in C#) for testing the logical equality of DTOs. This is considerably easier if the DTOs are structs (since ValueType.Equals does mostly the right thing) but that is not always appropriate. I would also like to override comparison of any IEnumerable objects (but not strings!) so that their contents are compared rather than their properties. This has proven to be harder than I would expect. Any hints will be greatly appreciated. I'll accept the answer that proves most useful or supplies a link to the most useful information. Thanks.

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  • Algorithm to generate all possible permutations of a list?

    - by LLer
    Say I have a list of n elements, I know there are n! possible ways to order these elements. What is an algorithm to generate all possible orderings of this list? Example, I have list [a, b, c]. The algorithm would return [[a, b, c], [a, c, b,], [b, a, c], [b, c, a], [c, a, b], [c, b, a]]. I'm reading this here http://en.wikipedia.org/wiki/Permutation#Algorithms_to_generate_permutations But Wikipedia has never been good at explaining. I don't understand much of it.

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  • Bandpass filter of FFT applied image. (Like ImageJ bandpass filter algorithm)

    - by maximus
    There is a good function that I need, which is implemented in Java program: ImageJ I need to understand the algorithm used there. The function has several parameters: link text And before using FFT it converts image to a special one: The Bandpass Filter uses a special algorithm to reduce edge artifacts (before the Fourier transform, the image is extended in size by attaching mirrored copies of image parts outside the original image, thus no jumps occur at the edges) Can you tell me more about this special transform? Actually tiling mirrored image. I am writing on C++ and wish to rewrite that part of the program on C++.

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  • Returning and instance of a Class given its .class (MyClass.class)

    - by jax
    I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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  • Database version control resources

    - by Wes McClure
    In the process of creating my own DB VCS tool tsqlmigrations.codeplex.com I ran into several good resources to help guide me along the way in reviewing existing offerings and in concepts that would be needed in a good DB VCS.  This is my list of helpful links that others can use to understand some of the concepts and some of the tools in existence.  In the next few posts I will try to explain how I used these to create TSqlMigrations.   Blogs entries Three rules for database work - K. Scott Allen http://odetocode.com/blogs/scott/archive/2008/01/30/three-rules-for-database-work.aspx Versioning databases - the baseline http://odetocode.com/blogs/scott/archive/2008/01/31/versioning-databases-the-baseline.aspx Versioning databases - change scripts http://odetocode.com/blogs/scott/archive/2008/02/02/versioning-databases-change-scripts.aspx Versioning databases - views, stored procedures and the like http://odetocode.com/blogs/scott/archive/2008/02/02/versioning-databases-views-stored-procedures-and-the-like.aspx Versioning databases - branching and merging http://odetocode.com/blogs/scott/archive/2008/02/03/versioning-databases-branching-and-merging.aspx Evolutionary Database Design - Martin Fowler http://martinfowler.com/articles/evodb.html Are database migration frameworks worth the effort? - Good challenges http://www.ridgway.co.za/archive/2009/01/03/are-database-migration-frameworks-worth-the-effort.aspx Continuous Integration (in general) http://martinfowler.com/articles/continuousIntegration.html http://martinfowler.com/articles/originalContinuousIntegration.html Is Your Database Under Version Control? http://www.codinghorror.com/blog/archives/000743.html 11 Tools for Database Versioning http://secretgeek.net/dbcontrol.asp How to do database source control and builds http://mikehadlow.blogspot.com/2006/09/how-to-do-database-source-control-and.html .Net Database Migration Tool Roundup http://flux88.com/blog/net-database-migration-tool-roundup/ Books Book Description Refactoring Databases: Evolutionary Database Design Martin Fowler signature series on refactoring databases. Book site: http://databaserefactoring.com/ Recipes for Continuous Database Integration: Evolutionary Database Development (Digital Short Cut) A good question/answer layout of common problems and solutions with database version control. http://www.informit.com/store/product.aspx?isbn=032150206X

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  • Is there a way to force ContourPlot re-check all the points on the each stage of it's recursion algorithm?

    - by Alexey Popkov
    Hello, Thanks to this excellent analysis of the Plot algorithm by Yaroslav Bulatov, I now understand the reason why Plot3D and ContourPlot fail to draw smoothly functions with breaks and discontinuities. For example, in the following case ContourPlot fails to draw contour x^2 + y^2 = 1 at all: ContourPlot[Abs[x^2 + y^2 - 1], {x, -1, 1}, {y, -1, 1}, Contours -> {0}] It is because the algorithm does not go deeply into the region near x^2 + y^2 = 1. It "drops" this region on an initial stage and do not tries to investigate it further. Increasing MaxRecursion does nothing in this sense. And even undocumented option Method -> {Refinement -> {ControlValue -> .01 \[Degree]}} does not help (but makes Plot3D a little bit smoother). The above function is just a simple example. In real life I'm working with very complicated implicit functions that cannot be solved analytically. Is there a way to get ContourPlot to go deeply into such regions near breaks and discontinuities?

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  • How does the rsync algorithm correctly identify repeating blocks?

    - by Kai
    I'm on a personal quest to learn how the rsync algorithm works. After some reading and thinking, I've come up with a situation where I think the algorithm fails. I'm trying to figure out how this is resolved in an actual implementation. Consider this example, where A is the receiver and B is the sender. A = abcde1234512345fghij B = abcde12345fghij As you can see, the only change is that 12345 has been removed. Now, to make this example interesting, let's choose a block size of 5 bytes (chars). Hashing the values on the sender's side using the weak checksum gives the following values list. abcde|12345|fghij abcde -> 495 12345 -> 255 fghij -> 520 values = [495, 255, 520] Next we check to see if any hash values differ in A. If there's a matching block we can skip to the end of that block for the next check. If there's a non-matching block then we've found a difference. I'll step through this process. Hash the first block. Does this hash exist in the values list? abcde -> 495 (yes, so skip) Hash the second block. Does this hash exist in the values list? 12345 -> 255 (yes, so skip) Hash the third block. Does this hash exist in the values list? 12345 -> 255 (yes, so skip) Hash the fourth block. Does this hash exist in the values list? fghij -> 520 (yes, so skip) No more data, we're done. Since every hash was found in the values list, we conclude that A and B are the same. Which, in my humble opinion, isn't true. It seems to me this will happen whenever there is more than one block that share the same hash. What am I missing?

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  • What algorithm should I use for encrypting and embedding a password for an application?

    - by vfclists
    What algorithm should I use for encrypting and embedding a password for an application? It obviously is not bullet proof, but it should be good enough to thwart someone scanning the database with a hex editor, or make it hard for someone who has the skills to use a debugger to trace the code to work out, either by scanning for the encrypted password, or using a debugger to run through the decryption code. Object Pascal would be nice. /vfclists

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  • QuickGraph - is there algorithm for find all parents (up to root vertex's) of a set of vertex's

    - by Greg
    Hi, In QuickGraph - is there algorithm for find all parents (up to root vertex's) of a set of vertex's. In other words all vertex's which have somewhere under them (on the way to the leaf nodes) one or more of the vertexs input. So if the vertexs were Nodes, and the edges were a depends on relationship, find all nodes that would be impacted by a given set of nodes. If not how hard is it to write one's own algorithms?

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  • User-Defined Customer Events & their impact (FA Type Profile)

    - by Rajesh Sharma
    CC&B automatically creates field activities when a specific Customer Event takes place. This depends on the way you have setup your Field Activity Type Profiles, the templates within, and associated SP Condition(s) on the template. CC&B uses the service point type, its state and referenced customer event to determine which field activity type to generate.   Customer events available in the base product include: Cut for Non-payment (CNP) Disconnect Warning (DIWA) Reconnect for Payment (REPY) Reread (RERD) Stop Service (STOP) Start Service (STRT) Start/Stop (STSP)   Note the Field values/codes defined for each event.   CC&B comes with a flexibility to define new set of customer events. These can be defined in the Look Up - CUST_EVT_FLG. Values from the Look Up are used on the Field Activity Type Profile Template page.     So what's the use of having user-defined Customer Events? And how will the system detect such events in order to create field activity(s)?   Well, system can only detect such events when you reference a user-defined customer event on a Severance Event Type for an event type Create Field Activities.     This way you can create additional field activities of a specific field activity type for user-defined customer events.   One of our customers adopted this feature and created a user-defined customer event CNPW - Cut for Non-payment for Water Services. This event was then linked on a Field Activity Type Profile and referenced on a Severance Event - CUT FOR NON PAY-W. The associated Severance Process was configured to trigger a reconnection process if it was cancelled (done by defining a Post Cancel Algorithm). Whenever this Severance Event was executed, a specific type of Field Activity was generated for disconnection purposes. The Field Activity type was determined by the system from the Field Activity Type Profile referenced for the SP Type, SP's state and the referenced user-defined customer event. All was working well until the time when they realized that in spite of the Severance Process getting cancelled (when a payment was made); the Post Cancel Algorithm was not executed to start a Reconnection Severance Process for the purpose of generating a reconnection field activity and reconnecting the service.   Basically, the Post Cancel algorithm (if specified on a Severance Process Template) is triggered when a Severance Process gets cancelled because a credit transaction has affected/relieved a Service Agreement's debt.   So what exactly was happening? Now we come to actual question as to what is the impact in having a user-defined customer event.   System defined/base customer events are hard-coded across the entire system. There is an impact even if you remove any customer event entry from the Look Up. User-defined customer events are not recognized by the system anywhere else except in the severance process, as described above.   There are few programs which have routines to first validate the completion of disconnection field activities, which were raised as a result of customer event CNP - Cut for Non-payment in order to perform other associated actions. One such program is the Post Cancel Algorithm, referenced on a Severance Process Template, generally used to reconnect services which were disconnected from other Severance Event, specifically CNP - Cut for Non-Payment. Post cancel algorithm provided by the product - SEV POST CAN does the following (below is the algorithm's description):   This algorithm is called after a severance process has been cancelled (typically because the debt was paid and the SA is no longer eligible to be on the severance process). It checks to see if the process has a completed 'disconnect' event and, if so, starts a reconnect process using the Reconnect Severance Process Template defined in the parameter.    Notice the underlined text. This algorithm implicitly checks for Field Activities having completed status, which were generated from Severance Events as a result of CNP - Cut for Non-payment customer event.   Now if we look back to the customer's issue, we can relate that the Post Cancel algorithm was triggered, but was not able to find any 'Completed' CNP - Cut for Non-payment related field activity. And hence was not able to start a reconnection severance process. This was because a field activity was generated and completed for a customer event CNPW - Cut for Non-payment of Water Services instead.   To conclude, if you introduce new customer events that extend or simulate base customer events, the ones that are included in the base product, ensure that there is no other impact either direct or indirect to other business functions that the application has to offer.  

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  • Limitations of User-Defined Customer Events (FA Type Profile)

    - by Rajesh Sharma
    CC&B automatically creates field activities when a specific Customer Event takes place. This depends on the way you have setup your Field Activity Type Profiles, the templates within, and associated SP Condition(s) on the template. CC&B uses the service point type, its state and referenced customer event to determine which field activity type to generate.   Customer events available in the base product include: Cut for Non-payment (CNP) Disconnect Warning (DIWA) Reconnect for Payment (REPY) Reread (RERD) Stop Service (STOP) Start Service (STRT) Start/Stop (STSP)   Note the Field values/codes defined for each event.   CC&B comes with a flexibility to define new set of customer events. These can be defined in the Look Up - CUST_EVT_FLG. Values from the Look Up are used on the Field Activity Type Profile Template page.     So what's the use of having user-defined Customer Events? And how will the system detect such events in order to create field activity(s)?   Well, system can only detect such events when you reference a user-defined customer event on a Severance Event Type for an event type Create Field Activities.     This way you can create additional field activities of a specific field activity type for user-defined customer events.   One of our customers adopted this feature and created a user-defined customer event CNPW - Cut for Non-payment for Water Services. This event was then linked on a Field Activity Type Profile and referenced on a Severance Event - CUT FOR NON PAY-W. The associated Severance Process was configured to trigger a reconnection process if it was cancelled (done by defining a Post Cancel Algorithm). Whenever this Severance Event was executed, a specific type of Field Activity was generated for disconnection purposes. The Field Activity type was determined by the system from the Field Activity Type Profile referenced for the SP Type, SP's state and the referenced user-defined customer event. All was working well until the time when they realized that in spite of the Severance Process getting cancelled (when a payment was made); the Post Cancel Algorithm was not executed to start a Reconnection Severance Process for the purpose of generating a reconnection field activity and reconnecting the service.   Basically, the Post Cancel algorithm (if specified on a Severance Process Template) is triggered when a Severance Process gets cancelled because a credit transaction has affected/relieved a Service Agreement's debt.   So what exactly was happening? Now we come to actual question as to what are limitations in having user-defined customer event.   System defined/base customer events are hard-coded across the entire system. There is an impact even if you remove any customer event entry from the Look Up. User-defined customer events are not recognized by the system anywhere else except in the severance process, as described above.   There are few programs which have routines to first validate the completion of disconnection field activities, which were raised as a result of customer event CNP - Cut for Non-payment in order to perform other associated actions. One such program is the Post Cancel Algorithm, referenced on a Severance Process Template, generally used to reconnect services which were disconnected from other Severance Event, specifically CNP - Cut for Non-Payment. Post cancel algorithm provided by the product - SEV POST CAN does the following (below is the algorithm's description):   This algorithm is called after a severance process has been cancelled (typically because the debt was paid and the SA is no longer eligible to be on the severance process). It checks to see if the process has a completed 'disconnect' event and, if so, starts a reconnect process using the Reconnect Severance Process Template defined in the parameter.    Notice the underlined text. This algorithm implicitly checks for Field Activities having completed status, which were generated from Severance Events as a result of CNP - Cut for Non-payment customer event.   Now if we look back to the customer's issue, we can relate that the Post Cancel algorithm was triggered, but was not able to find any 'Completed' CNP - Cut for Non-payment related field activity. And hence was not able to start a reconnection severance process. This was because a field activity was generated and completed for a customer event CNPW - Cut for Non-payment of Water Services instead.   To conclude, if you introduce new customer events, you should be aware that you don't extend or simulate base customer events, the ones that are included in the base product, as they are further used to provide/validate additional business functions.  

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  • Checksum Transformation

    The Checksum Transformation computes a hash value, the checksum, across one or more columns, returning the result in the Checksum output column. The transformation provides functionality similar to the T-SQL CHECKSUM function, but is encapsulated within SQL Server Integration Services, for use within the pipeline without code or a SQL Server connection. As featured in The Microsoft Data Warehouse Toolkit by Joy Mundy and Warren Thornthwaite from the Kimbal Group. Have a look at the book samples especially Sample package for custom SCD handling. All input columns are passed through the transformation unaltered, those selected are used to generate the checksum which is passed out through a single output column, Checksum. This does not restrict the number of columns available downstream from the transformation, as columns will always flow through a transformation. The Checksum output column is in addition to all existing columns within the pipeline buffer. The Checksum Transformation uses an algorithm based on the .Net framework GetHashCode method, it is not consistent with the T-SQL CHECKSUM() or BINARY_CHECKSUM() functions. The transformation does not support the following Integration Services data types, DT_NTEXT, DT_IMAGE and DT_BYTES. ChecksumAlgorithm Property There ChecksumAlgorithm property is defined with an enumeration. It was first added in v1.3.0, when the FrameworkChecksum was added. All previous algorithms are still supported for backward compatibility as ChecksumAlgorithm.Original (0). Original - Orginal checksum function, with known issues around column separators and null columns. This was deprecated in the first SQL Server 2005 RTM release. FrameworkChecksum - The hash function is based on the .NET Framework GetHash method for object types. This is based on the .NET Object.GetHashCode() method, which unfortunately differs between x86 and x64 systems. For that reason we now default to the CRC32 option. CRC32 - Using a standard 32-bit cyclic redundancy check (CRC), this provides a more open implementation. The component is provided as an MSI file, however to complete the installation, you will have to add the transformation to the Visual Studio toolbox by hand. This process has been described in detail in the related FAQ entry for How do I install a task or transform component?, just select Checksum from the SSIS Data Flow Items list in the Choose Toolbox Items window. Downloads The Checksum Transformation is available for SQL Server 2005, SQL Server 2008 (includes R2) and SQL Server 2012. Please choose the version to match your SQL Server version, or you can install multiple versions and use them side by side if you have more than one version of SQL Server installed. Checksum Transformation for SQL Server 2005 Checksum Transformation for SQL Server 2008 Checksum Transformation for SQL Server 2012 Version History SQL Server 2012 Version 3.0.0.27 – SQL Server 2012 release. Includes upgrade support for both 2005 and 2008 packages to 2012. (5 Jun 2010) SQL Server 2008 Version 2.0.0.27 – Fix for CRC-32 algorithm that inadvertently made it sort dependent. Fix for race condition which sometimes lead to the error Item has already been added. Key in dictionary: '79764919' . Fix for upgrade mappings between 2005 and 2008. (19 Oct 2010) Version 2.0.0.24 - SQL Server 2008 release. Introduces the new CRC-32 algorithm, which is consistent across x86 and x64.. The default algorithm is now CRC32. (29 Oct 2008) Version 2.0.0.6 - SQL Server 2008 pre-release. This version was released by mistake as part of the site migration, and had known issues. (20 Oct 2008) SQL Server 2005 Version 1.5.0.43 – Fix for CRC-32 algorithm that inadvertently made it sort dependent. Fix for race condition which sometimes lead to the error Item has already been added. Key in dictionary: '79764919' . (19 Oct 2010) Version 1.5.0.16 - Introduces the new CRC-32 algorithm, which is consistent across x86 and x64. The default algorithm is now CRC32. (20 Oct 2008) Version 1.4.0.0 - Installer refresh only. (22 Dec 2007) Version 1.4.0.0 - Refresh for minor UI enhancements. (5 Mar 2006) Version 1.3.0.0 - SQL Server 2005 RTM. The checksum algorithm has changed to improve cardinality when calculating multiple column checksums. The original algorithm is still available for backward compatibility. Fixed custom UI bug with Output column name not persisting. (10 Nov 2005) Version 1.2.0.1 - SQL Server 2005 IDW 15 June CTP. A user interface is provided, as well as the ability to change the checksum output column name. (29 Aug 2005) Version 1.0.0 - Public Release (Beta). (30 Oct 2004) Screenshot

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  • Implementing RSA-SHA1 signature algorithm in Java (creating a private key for use with OAuth RSA-SHA

    - by The Elite Gentleman
    Hi everyone, As you know, OAuth can support RSA-SHA1 Signature. I have an OAuthSignature interface that has the following method public String sign(String data, String consumerSecret, String tokenSecret) throws GeneralSecurityException; I successfully implemented and tested HMAC-SHA1 Signature (which OAuth Supports) as well as the PLAINTEXT "signature". I have searched google and I have to create a private key if I need to use SHA1withRSA signature: Sample code: /** * Signs the data with the given key and the provided algorithm. */ private static byte[] sign(PrivateKey key, String data) throws GeneralSecurityException { Signature signature = Signature.getInstance("SHA1withRSA"); signature.initSign(key); signature.update(data.getBytes()); return signature.sign(); } Now, How can I take the OAuth key (which is key = consumerSecret&tokenSecret) and create a PrivateKey to use with SHA1withRSA signature? Thanks

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