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• When can I be sure a directed graph is acyclic?

  - by Daniel Scocco

  The definition for directed acyclic graph is this: "there is no way to start at some vertex v and follow a sequence of edges that eventually loops back to v again." So far so good, but I am trying to find some premises that will be simpler to test and that will also guarantee the graph is acyclic. I came up with those premises, but they are pretty basic so I am sure other people figured it out in the past (or they are incorrect). The problem is I couldn't find anything related on books/online, hence why I decided to post this question. Premise 1: If all vertices of the graph have an incoming edge, then the graph can't be acyclic. Is this correct? Premise 2: Assume the graph in question does have one vertex with no incoming edges. In this case, in order to have a cycle, at least one of the other vertices would need to have two or more incoming edges. Is this correct?

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• To what extent do code-signing certificates boost sales of your software?

  - by Dan W

  In the experiences of everyone here, have you found a certificate to boost sales of your (downloadable) program? I produce .NET software and upon clicking the installation file, Windows 7 pops up a message saying the software is from an "unknown publisher" and to proceed with caution. For Windows 8, this appears to be even more prominent, and may adversely affect the number of downloads, and therefore the number of sales. A certificate will help soften this 'warning' by (for example) changing the warning's colour from orange to blue, and give the publisher's name instead of 'unknown'. But I'd like more tangible evidence since many people are obviously used to that message, and may not care and download anyway. So has anyone noticed a jump in sales after the switch?

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• Functional testing in the verification

  - by user970696

  Yesterday my question How come verification does not include actual testing? created a lot of controversy, yet did not reveal the answer for related and very important question: does black box functional testing done by testers belong to verification or validation? ISO 12207:12208 here mentiones testing explicitly only as a validation activity, however, it speaks about validation of requirements of the intended use. For me its more high level, like UAT test cases written by business users ISO mentioned above does not mention any specific verification (7.2.4.3.2)except for Requirement verification, Design verification, Document and Code & Integration verification. The last two can be probably thought as unit and integrated testing. But where is then the regular testing done by testers at the end of the phase? The book I mentioned in the original question mentiones that verification is done by static techniques, yet on the V model graph it describes System testing against high level description as a verification, mentioning it includes all kinds of testing like functional, load etc. In the IEEE standard for V&V, you can read this: Even though the tests and evaluations are not part of the V&V processes, the techniques described in this standard may be useful in performing them. So that is different than in ISO, where validation mentiones testing as the activity. Not to mention a lot of contradicting information on the net. I would really appreciate a reference to e.g. a standard in the answer or explanation of what I missed in the ISO. For me, I am unable to tell where the testers work belong.

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• How do I hire testers by giving them a buggy app for testing their efficiency?

  - by Jay

  My boss wants to recruit testers based on their testing efficiency (number of bugs identified). So, he's shortlisted 5 people and I need to give them an app full of bugs and see how they fare in reporting obvious bugs, and hidden bugs. I know.... it kind of sounds weird. I guess, this is just like the coding world, where you hire a programmer by assessing his/her programming ability (which is a little easier). Once hired, these testers would be testing a java swing app, so their familiarity of testing frameworks/tools is not really required. So, my question here is - How do I go about finding buggy apps (web/non-web), preferably java ones, that I can have the shortlisted testers have a go at? How would you go about this task if your boss asks you to do so? I am kind of clueless at this point - I googled a bit, thought about finding new apps on sourceforge with lots of bugs, but both approaches didn't work for me.

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• Verification of requirements question

  - by user970696

  Doing a lot of reading about V&V, I would need to clarify the following. A lot of definitons (less formal ones found in books) define verification like that: Verification: The software should conform to its specification. But then they speak about requirement verification, design verification etc. If I say that these items are "software" in terms of applying the definitons, what should I checked them against, what specification should requirements, which is the basic information, conform to? And one more thing: shouldnt be requirements also validated? To make sure they meets the customer needs? All texts I have speak only about SW validation on the end of the dev.process..

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• Is Haskell's type system an obstacle to understanding functional programming?

  - by Eric Wilson

  I'm studying Haskell for the purpose of understanding functional programming, with the expectation that I'll apply the insight that I gain in other languages (Groovy, Python, JavaScript mainly.) I choose Haskell because I had the impression that it is very purely functional, and wouldn't allow for any reliance on state. I did not choose to learn Haskell because I was interested in navigating an extremely rigid type system. My question is this: Is a strong type system a necessary by-product of an extremely pure functional language, or is this an unrelated design choice particular to Haskell? If it is the latter, I'm curious what would be the most purely functional language that is dynamically typed. I'm not particularly opposed to strong typing, it has its place, but I'm having a hard time seeing how it benefits me in this educational endeavor.

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• Real-time chat in Ruby on Rails

  - by Skydreamer

  First, I'm sorry because I know this question has been asked many times but I'm still looking forward to finding the answer to my problem. I'd want to implement a Real-time chat for my Rails app but I can't really host the server which handles the sockets. I've tried Faye but it needs a server. I've also heard of pusher but it's limited to 20 users at a time on the chat and I can't really be sure they won't be more. I've thought of irc but I think I can't really embed it into a rails app, maybe it needs sockets... So here's my problem, can I implement a real-time chat without owning a server ? What can you advice me ? Thank you for your answers.

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• Rails: Law of Demeter Confusion

  - by user2158382

  I am reading a book called Rails AntiPatterns and they talk about using delegation to to avoid breaking the Law of Demeter. Here is their prime example: They believe that calling something like this in the controller is bad (and I agree) @street = @invoice.customer.address.street Their proposed solution is to do the following: class Customer has_one :address belongs_to :invoice def street address.street end end class Invoice has_one :customer def customer_street customer.street end end @street = @invoice.customer_street They are stating that since you only use one dot, you are not breaking the Law of Demeter here. I think this is incorrect, because you are still going through customer to go through address to get the invoice's street. I primarily got this idea from a blog post I read: http://www.dan-manges.com/blog/37 In the blog post the prime example is class Wallet attr_accessor :cash end class Customer has_one :wallet # attribute delegation def cash @wallet.cash end end class Paperboy def collect_money(customer, due_amount) if customer.cash < due_ammount raise InsufficientFundsError else customer.cash -= due_amount @collected_amount += due_amount end end end The blog post states that although there is only one dot customer.cash instead of customer.wallet.cash, this code still violates the Law of Demeter. Now in the Paperboy collect_money method, we don't have two dots, we just have one in "customer.cash". Has this delegation solved our problem? Not at all. If we look at the behavior, a paperboy is still reaching directly into a customer's wallet to get cash out. EDIT I completely understand and agree that this is still a violation and I need to create a method in Wallet called withdraw that handles the payment for me and that I should call that method inside the Customer class. What I don't get is that according to this process, my first example still violates the Law of Demeter because Invoice is still reaching directly into Customer to get the street. Can somebody help me clear the confusion. I have been searching for the past 2 days trying to let this topic sink in, but it is still confusing.

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• Ways to break the "Syndrome of the perfect programmer"

  - by Rushino

  I am probably not the only one that feel that way. But I have what I tend to call "The syndrome of the perfect programmer" which many might say is the same as being perfectionist but in this case it's in the domain of programming. However, the domain of programming is a bit problematic for such a syndrome. Have you ever felt that when you are programming you're not confident or never confident enought that your code is clean and good code that follows most of the best practices ? There so many rules to follow that I feel like being overwhelmed somehow. Not that I don't like to follow the rules of course I am a programmer and I love programming, I see this as an art and I must follow the rules. But I love it too, I mean I want and I love to follow the rules in order to have a good feeling of what im doing is going the right way.. but I only wish I could have everything a bit more in "control" regarding best practices and good code. Maybe it's a lack of organization? Maybe it's a lack of experience? Maybe a lack of practice? Maybe it's a lack of something else someone could point out? Is there any way to get rid of that syndrome somehow ?

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• If you had three months to learn one relatively new technology, which one would you choose?

  - by Ivo van der Wijk

  This question was taken from CodingHorror. On my list would be (and some actually are): Android Development (and possibly iPhone development) Go language and its concurrency NoSQL, specifically CouchDB RCTK, which happens to be my own idea / project (but all ideas have been thought or already, what matters is my implementation) But I don't think I'm being cutting-edge/thinking-outside-the-box here. What's on your list? Please don't restrict yourself to the list above - that's my list. I'm interested in hearing what others find interesting new technology.

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• Why is the sudden increase in number of Git submitters on Debian popcorn graph in 2010-01?

  - by Jungle Hunter

  Almost every article I've read 1 comparing Git and Mercurial it seems like Mercurial has a better command line UX with each command being limited to one idea only (unlike say git checkout). But at some point Git suddenly became looking super popular and number of Git submitters on Debian popcorn graph (see graph image below) literally exploded. Source: Debian What happened in 2010-01 that things suddenly changed. Looks like GitHub was founded earlier than that - 2008.

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• ASP.NET Web Forms is bad, or what am I missing?

  - by iveqy

  Being a PHP guy myself I recently had to write a spider to an asp.net site. I was really surprised by the different approach to ajax and form-handling. For example, in the PHP sites I've worked with, a deletion of a database entry would be something like: GET delete.php?id=&confirm=yes and get a "success" back in some form (in the ajax case, probably a json reply). In this asp.net application you would instead post a form, including all inputs on the page, with a huge __VIEWSTATE and __EVENTVALIDATION. This would be more than 10 times as big as above. The reply would be the complete side again, with a footer containing some structured data for javascript to parse and display the result. Again, the whole page is sent, and then throwed away(?) since it's already displayed. Why not just send the footer with the data to parse (it's not json nor xml but a | separated list). I really can't see why you would design a system that way. Usually you've a fast client, and a somewhat fast server but a really slow connection. Why not keep the datatransfer to a minimum? Why those huge __VIEWSTATE and __EVENTVALIDATION? It seems that everything is done way to chatty and way to complicated. I really can't see the point and that usually means that I'm missing something. So please tell me, what are the reasons for this design and what benefits (and weaknesses) does it have? (Yes I know that __VIEWSTATE is used to tell what type of form-konfiguration should be sent back to the server. But WHY is this needed?) Please keep this discussion strictly technical and avoid flamewars. Update: Please excuse the somewhat rantish question. I tried to explain my view to be able to get a better answer. I am not saying that asp.net is bad, I am saying that I don't understand the meaning of those concepts. Usually that means that I've things to learn instead of the concepts beeing wrong. I appreciate the explanations about that "you don't have to do this way in asp.net", I'll read up on MVC and other .net technologies. However, there most be a reason for this site (the one I referred to) to be written the way it is. It's written by professionals for a big organisation with far more experience than what I've. Any explanation about their (possible) design choice would be welcome.

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• Get Info From Database, or Build Inferred Info?

  - by Zaemz

  Does it make more sense to store and retrieve properties or information directly related to an item in a database, or, say in such a case that a product's ID could describe information about it, should the information be gathered from that? Example: Item SKU -- 4HBU12 4 - is the number of motors H - the voltage B - the color, blue U - the model 12 - the length Should I store those individual attributes as well as the SKU, or should I store only the SKU and build the attributes from it?

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• How does affliate marketing work, technically?

  - by Ron Gonzales

  There are lots of companies like Commision Junction that let you sell other people's products for a commission. How do these programs work, technically? Ie, are you simply given a link to the product you want to sell with an embedded ID in the URL? Does it involve cookies somehow? Do you take the order yourself and forward the information to the actual supplier of the goods/services? And how do you know if the program or the 'affliate network' isn't ripping you off by not creditting you for a sale?

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• Comparison of languages by usage type?

  - by Tom

  Does anyone know of a good place to go find comparisons of programming languages by the intended platform/usage? Basically, what I want to know, is of the more popular languages, which ones are meant for high level application development, low level system development, mobile development, web, etc. If there's a good listing out there already, I'm not finding it so far. Does anyone know of a place that would have this? Thanks.

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• how to make audio and video streaming servers work?

  - by explorex

  I am a php mysql developer ... just an (below) average. and i am interested in the way television and radio are broadcasted over internet live. i want to know how it works and and what are its requirements (which package of which programming language offers the best). i must admit that i am a complete layman but i expect it do by next half month or year or so. And please clarify me Websites are stored in servers. From my desktop, i want to broadcast some video, then i need to connect to webserver(to upstream the video). Is there an application to do that (or do i have to code that or embed in my web application and which programming language would be suitable(does python support that))? and i also need a script to handle the upstreamed video or audio(can i do that with php)?

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• Will knowing just Magento ruin my career?

  - by Devendra Sharma

  Hello everyone, I have some career doubts and need your kind advise. I have just started my career in PHP. A company is offering a job to me as Magento developer, but the condition is that i have to stay with the company for atleast one year. This company just works on Magento. I doubt, that after a year, I would be knowing just Magento and nothing else in php. Please guide me that should i join the company or not.

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• What are some reasonable stylistic limits on type inference?

  - by Jon Purdy

  C++0x adds pretty darn comprehensive type inference support. I'm sorely tempted to use it everywhere possible to avoid undue repetition, but I'm wondering if removing explicit type information all over the place is such a good idea. Consider this rather contrived example: Foo.h: #include <set> class Foo { private: static std::set<Foo*> instances; public: Foo(); ~Foo(); // What does it return? Who cares! Just forward it! static decltype(instances.begin()) begin() { return instances.begin(); } static decltype(instances.end()) end() { return instances.end(); } }; Foo.cpp: #include <Foo.h> #include <Bar.h> // The type need only be specified in one location! // But I do have to open the header to find out what it actually is. decltype(Foo::instances) Foo::instances; Foo() { // What is the type of x? auto x = Bar::get_something(); // What does do_something() return? auto y = x.do_something(*this); // Well, it's convertible to bool somehow... if (!y) throw "a constant, old school"; instances.insert(this); } ~Foo() { instances.erase(this); } Would you say this is reasonable, or is it completely ridiculous? After all, especially if you're used to developing in a dynamic language, you don't really need to care all that much about the types of things, and can trust that the compiler will catch any egregious abuses of the type system. But for those of you that rely on editor support for method signatures, you're out of luck, so using this style in a library interface is probably really bad practice. I find that writing things with all possible types implicit actually makes my code a lot easier for me to follow, because it removes nearly all of the usual clutter of C++. Your mileage may, of course, vary, and that's what I'm interested in hearing about. What are the specific advantages and disadvantages to radical use of type inference?

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• What is a good way to share internal helpers?

  - by toplel32

  All my projects share the same base library that I have build up over quite some time. It contains utilities and static helper classes to assist them where .NET doesn't exactly offer what I want. Originally all the helpers were written mainly to serve an internal purpose and it has to stay that way, but sometimes they prove very useful to other assemblies. Now making them public in a reliable way is more complicated than most would think, for example all methods that assume nullable types must now contain argument checking while not charging internal utilities with the price of doing so. The price might be negligible, but it is far from right. While refactoring, I have revised this case multiple times and I've come up with the following solutions so far: Have an internal and public class for each helper The internal class contains the actual code while the public class serves as an access point which does argument checking. Cons: The internal class requires a prefix to avoid ambiguity (the best presentation should be reserved for public types) It isn't possible to discriminate methods that don't need argument checking   Have one class that contains both internal and public members (as conventionally implemented in .NET framework). At first, this might sound like the best possible solution, but it has the same first unpleasant con as solution 1. Cons: Internal methods require a prefix to avoid ambiguity   Have an internal class which is implemented by the public class that overrides any members that require argument checking. Cons: Is non-static, atleast one instantiation is required. This doesn't really fit into the helper class idea, since it generally consists of independent fragments of code, it should not require instantiation. Non-static methods are also slower by a negligible degree, which doesn't really justify this option either. There is one general and unavoidable consequence, alot of maintenance is necessary because every internal member will require a public counterpart. A note on solution 1: The first consequence can be avoided by putting both classes in different namespaces, for example you can have the real helper in the root namespace and the public helper in a namespace called "Helpers".

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• Software development project inception phase

  - by john ryan

  Currently our team develops Web Applications and now we are going to Windows Forms applications. I have created the inception phase for our Windows Forms project structure. eg: ApplicationSolution --> Security Project(Login Authentication) a. Users will be registered with different applications in our application database. eg: ProjectApplicationId|ProjectName | UserId 1 |ProjectApplication1| user 2 |ProjectApplication2| user b. Execute Application (Start) c. On Security dialog, application automatically get the userid of the user and see all the application it is registered using System.Security.Principal.WindowsIdentity.GetCurrent() eg: Prototype Welcome User! Please Choose Appliations you are registered on below: ProjectApplication1 <--this will be a dropdown ProjectApplication2 Password: [*********************] [Access Application Button] d. User selects the application with its password e. If the password is incorrect (application.exit()) else execute Selected Application eg: ProjectApplication1 is selected then execute ProjectApplication1 --> ProjectApplication1 --> ProjectApplication2 --> Many to come ++ if ProjectApplications has been closed then restart security Application. My questions on this use case: Is my use case possible? Can you give me any recommendations ? Currently we use setup and deployment to create installer in each Windows Forms application.

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• How do I classify using SVM Classifier in Matlab?

  - by Gomathi

  I'm on a project of liver tumor segmentation and classification. I used Region Growing and FCM for liver and tumor segmentation respectively. Then, I used Gray Level Co-occurence matrix for texture feature extraction. I have to use Support Vector Machine for Classification. But I don't know how to normalize the feature vectors. Can anyone tell how to program it in Matlab? To the GLCM program, I gave the tumor segmented image as input. Was I correct? If so, I think, then, my output will also be correct. I gave the parameters exactly as in the example provided in the documentation itself. The output I obtained was stats = autoc: [1.857855266614132e+000 1.857955341199538e+000] contr: [5.103143332457753e-002 5.030548650257343e-002] corrm: [9.512661919561399e-001 9.519459060378332e-001] corrp: [9.512661919561385e-001 9.519459060378338e-001] cprom: [7.885631654779597e+001 7.905268525471267e+001] cshad: [1.219440700252286e+001 1.220659371449108e+001] dissi: [2.037387269065756e-002 1.935418927908687e-002] energ: [8.987753042491253e-001 8.988459843719526e-001] entro: [2.759187341212805e-001 2.743152140681436e-001] homom: [9.930016927881388e-001 9.935307908219834e-001] homop: [9.925660617240367e-001 9.930960070222014e-001] maxpr: [9.474275457490587e-001 9.474466930429607e-001] sosvh: [1.847174384255155e+000 1.846913030238459e+000] savgh: [2.332207337361002e+000 2.332108469591401e+000] svarh: [6.311174784234007e+000 6.314794324825067e+000] senth: [2.663144677055123e-001 2.653725436772341e-001] dvarh: [5.103143332457753e-002 5.030548650257344e-002] denth: [7.573115918713391e-002 7.073380266499811e-002] inf1h: [-8.199645492654247e-001 -8.265514568489666e-001] inf2h: [5.643539051044213e-001 5.661543271625117e-001] indnc: [9.980238521073823e-001 9.981394883569174e-001] idmnc: [9.993275086521848e-001 9.993404634013308e-001] The thing is, I run the program for three images. But all three gave me the same output. When I used graycoprops() stat = Contrast: 4.721877658740964e+005 Correlation: -3.282870417955449e-003 Energy: 8.647689474127760e-006 Homogeneity: 8.194621855726478e-003 stat = Contrast: 2.817160447307697e+004 Correlation: 2.113032196952781e-005 Energy: 4.124904827799189e-004 Homogeneity: 2.513567163994905e-002 stat = Contrast: 7.086638436309059e+004 Correlation: 2.459637878221028e-002 Energy: 4.640677159445994e-004 Homogeneity: 1.158305728309460e-002 The images are:

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• What programming language should I learn for fun?

  - by Bo Milanovich

  Disclaimer: I'm not a programmer, but I do like coding from time to time. This is strictly for fun, nothing else. I'm an economist :) I learned Delphi in the past (7 years ago, forgot 99% of it), BASIC (10 years ago). I now know a bit of PHP. So I want to learn a programming language just so I can kill some time, but it'd be awesome if it would be useful as well. I've narrowed down choices to the following: Python (heard it was easy yet useful, Google's appengine runs on python) Java (awesome because cross-platform and very popular, also I'm an Android fan so I might even develop some apps) Continue learning PHP? (awesome language, I'm a web developer somewhat so it may be useful) Something else? Thanks!

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• How do you achieve a numeric versioning scheme with Git?

  - by Erlend

  My organization is considering moving from SVN to Git. One argument against moving is as follows: How do we do versioning? We have an SDK distribution based on the NetBeans Platform. As the svn revisions are simple numbers we can use them to extend the version numbers of our plugins and SDK builds. How do we handle this when we move to Git? Possible solutions: Using the build number from hudson (Problem: you have to check hudson to correlate that to an actual git version) Manually upping the version for nightly and stable (Problem: Learning curve, human error) If someone else has encountered a similar problem and solved it, we'd love to hear how.

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• Dealing with an Idiot [closed]

  - by inspectorG4dget

  I'm a 4th year University Computer Science student, and I have this problem, that I don't seem to be able to find a straight answer to: As a 4th year computer science student, I spend more time in the computer lab on campus, than even my own home. This means that getting along with everyone else here is very important to me. In most cases, this is not an issue because my interactions with almost all the people here fall into one of the following categories: Let me help you, junior Hi fellow student in a course I'm taking, I'm having trouble with this assignment question. Can you give me a hint as to how you solved it? Hi fellow student in a course I'm taking, This is how I solved the problem that you're stuck on. Hope it helps Hi fellow student, I noticed that you're working on a project, using a library that I'm interested in. Can we setup a time so I can learn about this library from you? This model of interaction works very well for me. However, there is one fellow student, who manages to make my life hell beyond all of this (his name is not important, let's just call him "Sam"). He seems to be always (pardon my crass description) high and completely unwilling to contribute to a constructive, academic conversation. He's a pretty smart guy, but just comes across as (I hate to say something like this about a fellow student, but) an imbecile. He also has ignorant opinions on important topics, some of which pertain to my specialization (AI, NLP, etc), and when I try to explain to him why he's wrong, all he does is insult me and put me in a foul mood. I have tried ignoring him (sitting somewhere else in the lab, headphones, etc), but he seems to like doing this because he approaches me and no amount of "leave me alone" seems to do the trick. Can anyone please suggest to me how to deal with this man in a civil way? Thank you

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• Japanese Multiplication simulation - is a program actually capable of improving calculation speed?

  - by jt0dd

  On SuperUser, I asked a (possibly silly) question about processors using mathematical shortcuts and would like to have a look at the possibility at the software application of that concept. I'd like to write a simulation of Japanese Multiplication to get benchmarks on large calculations utilizing the shortcut vs traditional CPU multiplication. I'm curious as to whether it makes sense to try this. My Question: I'd like to know whether or not a software math shortcut, as described above is actually a shortcut at all. This is a question of programming concept. By utilizing the simulation of Japanese Multiplication, is a program actually capable of improving calculation speed? Or am I doomed from the start? The answer to this question isn't required to determine whether or not the experiment will succeed, but rather whether or not it's logically possible for such a thing to occur in any program, using this concept as an example. My theory is that since addition is computed faster than multiplication, a simulation of Japanese multiplication may actually allow a program to multiply (large) numbers faster than the CPU arithmetic unit can. I think this would be a very interesting finding, if it proves to be true. If, in the multiplication of numbers of any immense size, the shortcut were to calculate the result via less instructions (or faster) than traditional ALU multiplication, I would consider the experiment a success.

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