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  • Optimizing sparse dot-product in C#

    - by Haggai
    Hello. I'm trying to calculate the dot-product of two very sparse associative arrays. The arrays contain an ID and a value, so the calculation should be done only on those IDs that are common to both arrays, e.g. <(1, 0.5), (3, 0.7), (12, 1.3) * <(2, 0.4), (3, 2.3), (12, 4.7) = 0.7*2.3 + 1.3*4.7 . My implementation (call it dict) currently uses Dictionaries, but it is too slow to my taste. double dot_product(IDictionary<int, double> arr1, IDictionary<int, double> arr2) { double res = 0; double val2; foreach (KeyValuePair<int, double> p in arr1) if (arr2.TryGetValue(p.Key, out val2)) res += p.Value * val2; return res; } The full arrays have about 500,000 entries each, while the sparse ones are only tens to hundreds entries each. I did some experiments with toy versions of dot products. First I tried to multiply just two double arrays to see the ultimate speed I can get (let's call this "flat"). Then I tried to change the implementation of the associative array multiplication using an int[] ID array and a double[] values array, walking together on both ID arrays and multiplying when they are equal (let's call this "double"). I then tried to run all three versions with debug or release, with F5 or Ctrl-F5. The results are as follows: debug F5: dict: 5.29s double: 4.18s (79% of dict) flat: 0.99s (19% of dict, 24% of double) debug ^F5: dict: 5.23s double: 4.19s (80% of dict) flat: 0.98s (19% of dict, 23% of double) release F5: dict: 5.29s double: 3.08s (58% of dict) flat: 0.81s (15% of dict, 26% of double) release ^F5: dict: 4.62s double: 1.22s (26% of dict) flat: 0.29s ( 6% of dict, 24% of double) I don't understand these results. Why isn't the dictionary version optimized in release F5 as do the double and flat versions? Why is it only slightly optimized in the release ^F5 version while the other two are heavily optimized? Also, since converting my code into the "double" scheme would mean lots of work - do you have any suggestions how to optimize the dictionary one? Thanks! Haggai

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  • Java GC: top object classes promoted (by size)?

    - by Java Geek
    Hello! Please let me know what is the best way to determine composition of young generation memory promoted to old generation, after each young GC event? Ideally I would like to know class names which are responsible say, for 80% of heap in each "young gen - old gen" promotion chunk; Example: I have 600M young gen, each tenure promotes 6M; I want to know which objects compose this 6M. Thank you.

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  • Geometry library for python (or C++) for CAD-like operations?

    - by gct
    I'm trying to put together a simple program that will let me visualize a series of consecutive cuts on a wood panel using a router with a particular cutting head. I'm trying to find a decent geometry library that will give me a shortcut through the CAD-like stuff. Specifically, I'd like to be able to define a rectangular solid (the wood panel) and then define a bit profile shape, and take cuts through the rectangular solid (sometimes on a straight line, sometimes on a circular arc). Does anyone know of anything that will do this?

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  • Is it possible to store only a checksum of a large file in git?

    - by Andrew Grimm
    I'm a bioinformatician currently extracting normal-sized sequences from genomic files. Some genomic files are large enough that I don't want to put them into the main git repository, whereas I'm putting the extracted sequences into git. Is it possible to tell git "Here's a large file - don't store the whole file, just take its checksum, and let me know if that file is missing or modified." If that's not possible, I guess I'll have to either git-ignore the large files, or, as suggested in this question, store them in a submodule.

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  • What does the following line of a bash script do?

    - by Bialecki
    Usually work in Windows, but trying to setup RabbitMQ on my Mac. Can someone let me know what the line below does? [ "x" = "x$RABBITMQ_NODE_IP_ADDRESS" ] && [ "x" != "x$NODE_IP_ADDRESS" ] && RABBITMQ_NODE_IP_ADDRESS=${NODE_IP_ADDRESS} Specifically, I'm curious about the [ "x" = "x$RAB..."] syntax.

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  • GAE messaging service

    - by cometta
    let say i want my corporate server to communicate with google app engine vise verse. I know that gae do not support JMS,RMI etc. what is the best alternative for this kind of communication?(i think http get is not suitable for this kind of communicate) use task queue? both my corporate server and gae application using spring framework

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  • Drupal: cusomizing modules question

    - by Patrick
    hi, I've a question about how to customize drupal modules avoiding hacks. Let's say I've downloaded Lightbox2 module and I want to change the javascript file to display differently my lightbox. At the moment I'm modifying the Lightbox2 module, so I cannot update it anymore, so I know it is not the best practice. I was wondering if I can customize the javascript file of this module with a hook, and how. Thanks

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  • turning off sleep mode on kindle?

    - by pfunc
    I'm just getting into kindle development, and I want to know if it is possible to turn off kindle's sleep mode? Or is there a way to wake it up (or a way to program it to wake up) by pushing the buttons on the front, rather than using the power button? Not looking for anything to in-depth here, just point me in the right direction or let me know if it is possible.

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  • jquery accessibility option

    - by Val
    what do you guys think of this code to help with some lazy people out there :) $('a').each(function (i,n){ $title = $(n).attr('title'); if(!$title){ $(n).attr('title',$(n).html()); } }); Considering that most links have the same title as their text so... let me knwo if any of you out there like this? So we can tell w3school one box ticked :)

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  • what are the devises will be listed

    - by barbgal
    Hi.. please let me know what are the devices wil be listed using the below code guid = GUID_DEVINTERFACE_VOLUME; // Get device Information handle for Volume interface hDevInfo = SetupDiGetClassDevs( &guid, NULL, NULL, DIGCF_DEVICEINTERFACE | DIGCF_PRESENT ); Thank you

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  • get greatest prime factor in F#

    - by Alex
    I had VS 11 beta and the following code was working without problem: let rec fac x y = if (x = y) then y elif (x % y = 0I) then fac (x / y) y else fac x / (y + 1I);; Now I installed VS 2012 RC and I get the following error: The type 'System.Numerics.BigInteger -> System.Numerics.BigInteger' is not compatible with the type 'System.Numerics.BigInteger' Is code not correct or F# interactive? It's F# 3.0.

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  • How to display full documentation of a method as you type in VS?

    - by drasto
    The title is pretty descriptive... Is there any extension that let me see FULL documentation of the method I'm typing ? I would like to see the documentation as I can see it in Object Browser with description of parameters and everything not just some "summary". So what I'd like to see when I type String.Format is: Of cause with an option to see all overrides. It may be part of intelisence or I don't know what it does not really matter.

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  • .Net OpenXml - Write Word 2007 document

    - by Melursus
    My problem is in two parts. 1. First part How can I, in Word 2007, put an id on a section so I can easy access this section from my code ? Let say I got Name : Here I want to set the name from my c# code 2. Second part How can I, from my c# code, fill this section id ?

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  • How can I move deleting photos to the background with delayed_job and paperclip

    - by Tam
    I let my users create photo albums with many photos. Relationship as follows: has_many :album_photos, :dependent => :destroy i upload photos to S3 When the user delete album I want to delete all photos as the relationship shows but it takes time if the user has many photos. Can I automatically set photo deletion to happen in the background (delayed_job) without having to manually call 'send_later' on every photo?

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  • How to get if the object is already retrieved in inject

    - by zerkms
    Is it possible to know that particular dependency already has been satisfied by ninject kernel? To be clear: Let's suppose we have this module: Bind<IA>().To<A>(); Bind<IB>().To<B>(); And some "client"-code: var a = kernel.Get<IA>(); // how to get here "true" for assumption: "IA was requested (once)" // and "false" for: "IB was not requested ever"

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  • Android moving back to first activity on button click

    - by cppdev
    I am writing a application where I am dealing with 4 activities, let's say A, B, C & D. Activity A invokes B, B invokes C, C invokes D. On each of the activity, I have a button called "home" button. When user clicks on home button in any of the B, C, D activities, application should go back to A activity screen ? How to simulate "home" button in this case ?

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