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  • What's a good way to add a large number of small floats together?

    - by splicer
    Say you have 100000000 32-bit floating point values in an array, and each of these floats has a value between 0.0 and 1.0. If you tried to sum them all up like this result = 0.0; for (i = 0; i < 100000000; i++) { result += array[i]; } you'd run into problems as result gets much larger than 1.0. So what are some of the ways to more accurately perform the summation?

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  • How can I add floats together in different orders, and always get the same total?

    - by splicer
    Let's say I have three 32-bit floating point values, a, b, and c, such that (a + b) + c != a + (b + c). Is there summation algorithm, perhaps similar to Kahan summation, that guarantees that these values can be summed in any order and always arrive at the exact same (fairly accurate) total? I'm looking for the general case (i.e. not a solution that only deals with 3 numbers). Is arbitrary precision arithmetic the only way to go? I'm dealing with very large data sets, so I'd like to avoid the overhead of using arbitrary precision arithmetic if possible. Thanks!

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  • PHP: Is_numeric returns false on 0

    - by Industrial
    Hi everyone, Is_numeric() as well as is_int() returns false if the value is 0. What can i do instead to verify that a specific value is numbers only in PHP? Are we heading straight for the Regular Expressions camp, or are there some nice, handy feature for this out there already? Thanks!

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  • SAPPHIRE NOW : SAP ouvre un site pour tester HANA, sa solution de In-Memory Computing au coeur de sa "stratégie d'innovation"

    SAPPHIRE NOW : SAP ouvre un site pour tester HANA Sa solution de In-Memory Computing au coeur de sa « stratégie d'innovation » Autre jour, autre ambiance au SAPPHIRE NOW de SAP qui se tient actuellement à Madrid. Si la présentation de Jim Hagemann Snabe, hier, était placée sous le signe de la sciences fiction, celle de Vishal Sikka, membre exécutive du Board de SAP, était aujourd'hui placé sous celui de la mythologie et de la Grèce antique. Le message, en revanche, confirmait celui introduit par le le co-PDG de la société : Cloud, Mobilité et In-Memory so...

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  • Sortie de la version 0.7 de Apache Cassandra, le SGBD NoSQL phare du Cloud Computing, utilisé par Facebook et Twitter

    Sortie de la version 0.7 de Apache Cassandra Le SGBD NoSQL phare du Cloud Computing, utilisé par Facebook et Twitter Mise à jour du 12/01/2011 par Idelways La fondation Apache vient d'annoncer la disponibilité de la version 0.7 de Cassandra, le système de gestion de base de donnée de type NoSQL conçu pour supporter des quantités massives de données. Parmi les nouveautés de cette version, l'arrivée des Indexs Secondaires, une manière efficace d'exécuter des requêtes sur des noeud locaux de stockages côté client. Autre nouveauté, le support des « Large Row », qui permettent d'avoir jusqu'à 2 milliards de co...

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  • Oracle Cloud Computing Summit? 6/15 ?·????????????

    - by kiyoshi.nira
    ????·???????????????????????????????????????????????????????????????????????????????????????????????????·??????????????????? ??????????? ?? : 2010?6?15?(?) 10:00~16:30(????:9:30~) ?? : ?·???????????? (map) ?105-8563 ????????4-8-1 ?? : CIO?????????????IT??????????????????????????????????? ???: ??(?????) ??????????? -> Oracle Cluod computing Summit

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  • How do you explain more advanced computing concepts to a non super user?

    - by EvilChookie
    I often have to explain computing concepts to non super users, and I often do it by relating computing concepts to real life situations. I wouldn't mind seeing how other super users do it, and some really good explanations might come in handy instead of me having to wing it. So, how do you explain advanced computing topics to the 'normal' people? Notes: One explanation per answer, and let the best float to the top. CW turned on, since this is subjective. Also, feel free to edit my tags if you can think of better ones =)

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  • Windows RPC vs XML-RPC

    - by Y.Z
    Is there any benchmark about encoding/decoding certain common typed data in Microsoft RPC NDR engine (DCE 1.1) in comparison with that in XML-RPC-C/C++ in the de-facto C/C++ implementation in XML-RPC? Actually I have to choose between Windows RPC and XML-RPC-C/C++ to implement my own common object infrastructure for High Performance Computing on Windows. Any recommandation about which with regard to their performance? Thank you. Best Regards, Yang

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  • auto updating software on cloud.

    - by iamgopal
    I know wordpress,joomla,drupal etc ( most of php_mysql stack ) can auto detect update in software itself or/and plugin and either ask for user permission to update or auto update it. How to do similar thing on google app engine like cloud computing ? I am creating an open source software which is targeted towards non-computer people. who can not clone my code and update their application easily. what is the easier way to do this ?

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  • Can computer clusters be used for general everyday applications?

    - by Matt Pascoe
    Does anyone know how a computer cluster can be used for everyday applications, like for example video games? I would like to build a computer cluster that can run applications over the cluster that were not specifically designed for computer clusters and still see the performance increase. One use would be for video games, but I would also like to utilize the increased computing power for running a large network of virtualized machines.

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  • Choice of operating systems for a Rackspace cloud installation

    - by riteshmnayak
    I am planning to use Rackspace cloud services to host a java web application and also run apace for wordpress and trac. What would be a stable operating system to host such an application. My requirements are that the core OS bundle should be minimalistic (so I can install only what I want), consume very little memory and be performant. I would also need it to contain softwares for the common lamp stack, J2EE stack etc. A supported package manager would be lovely. My choices are listed below. RHEL 5.3 or 5.4 Debian Lenny Ubuntu 8.04 onwards Centos 5.3 or 5.4 Arch 2009.02 Gentoo 2008.0 or 10.1 Fedora 11 or 12 PS: can somebody add the rackspace tag to this? Edit to remove this line as well. Thanks

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  • Mac Management and Security

    - by Bart Silverstrim
    I was going through some literature on managing OS X laptops and asked someone some questions about usage scenarios when using the MacBooks. I asked someone more knowledgeable than I about whether it was possible for my Mac to be taken over if I were visiting another site for a conference or if I went on a wifi network at a local coffee house with policies from an OS X Server with workgroup manager (either legit for the site or someone running a version of OS X Server on hardware they have hidden somewhere on the network), which apparently could be set up to do things like limit my access to Finder or impose other neat whiz-bang management features. He said that it is indeed possible for it to happen as it would be assigned via the DHCP server and the OS X server would assume my Mac is a guest and could hand out restrictions and apparently my Mac will happily accept them without notifying me or giving me an option, unlike Windows which I believe would need to be joined to a domain before it becomes "managed" by Active Directory. So my question is as network admins and sysadmins with users traveling with MacBooks, is there a way to reasonably protect your users from having their machines hijacked without resorting to just turning off networking all the time? Or isn't this much of a security hazard? What threat does this pose to the road warriors in your businesses?

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  • Automatically Login & Startup A Windows Program On Amazon's EC2 Service

    - by darkAsPitch
    How can I automatically start a program on Amazon's EC2 Windows 2008 web servers? For example, if I wanted to test the "Digg effect" on a web page of mine, how could I open 100 windows 2008 servers at once, each loading one (or two?) instances of the firefox web browser? I have placed a sample batch file in the windows startup folder that echos the time it was called, but it is only started when I actually login remotely via the remote desktop protocol. I don't want to have to login to 100 servers to get my software to run :P What can I do? I am using this Windows 2008 Datacenter, Amazon-supplied AMI specifically: ami-a2698bcb

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  • Linux & Windows Boot Up Times in Amazon Web Service and Windows Azure

    - by Adron
    I've been working with Windows Azure and Amazon Web Services EC2 for a good many months now (almost getting to the years range) and I've seen something over and over that seems troubling. With AWS & Linux I commonly get instance startup times with EC2 around the 1-3 minute range. With AWS & Windows OS on an EC2 instance it often takes 10-20 minutes. With Windows Azure Web or Service Role I often get anywhere from 6-30 minutes waiting for a role to startup. I assume of course this involves booting up a windows instance somewhere in the fabric. I know there has always been tons of FUD about windows vs. Linux, but I'd really like to know why it is that Windows 08 or 03 boots so much slower in the cloud than Linux. Any specific technical information regarding this would be greatly appreciated! Thanks.

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  • Comparison of cloud hosting providers

    - by Abel
    Is there a place where we can compare* the many new arising cloud hosting providers? From reading into each of them, they seem very different and range from just hosting applications (google) to a semi-full enterprise web serving framework (rackspace). Comparing "by hand" takes a lot of time. All have limitations and different prizing, but which are those and how do they compare? I'm looking for an unbiased comparison site, rather then a discussion on "which is the best". * I don't mean a hosting provider comparison site, of which there are many. The properties of cloud hosting providers are remarkably different and don't compare well on classical hosting provider comparison charts.

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  • Raid-1 Western Digital Green AARS, cloning and WD Align Utility

    - by Jaguar
    Hello all, My current setup runs on top of 2x Western Digital 2500KS drives on Raid-1, using the motherboard's 780G raid controller, on WinXP. Everything is fine, but the drives are a bit noisy. I am considering buying 2x WD6400AARS disks which are the 640GB slower 'green' drives, but also feature the Advanced Formatting 4KB sectors. This means that for WinXP the partition will have to be aligned to work properly, else there is a performance penalty. There are 2 questions here: The Green drives from WD are all slower and are (according to WD) susceptible to drop-out's from the controller. Has anyone any experience in this matter? Is there a possibility the controller will drop a drive? If so, can i do anything about it? Secondly, western digital gives a utility to perform the alignment on the partition. The thing is, will the utility see the drives in question as the operating system only sees 1 logical disk? I will be making the transition using a cloning tool (most probably norton ghost) unless i don't find a solution or a clear answer, in which case i'll just buy a win 7 license and make a clean install... thx in advance

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  • MySql Data Loss - post mortem analysis - RackSpace Cloud Server

    - by marfarma
    After a recent 'emergency migration' of a RS cloud server, the mysql databases on our server snapshot image proved to be days out of date from the backup date. And yet files that were uploaded through the impacted webapp had been written to the file system. Related metadata that was written to the database was lost, but the files themselves were backed-up. Once I was able to manually access the mysql data files before the mysql server started (server was configured to start mysql on boot), I was able to see that the update time for ib_logfile1, ib_logfile0 and ibdata1 was days old. As with this poster, mysql data loss after server crash, it's as if some caching controller had told the OS / mysql server that it had committed data that was still in cache, and it was lost instead of flushed. I can't quite wrap my head around how the uploaded files got written but the database data did not. I would have thought that any cache would have flushed system wide, rather than process by process. Any suggestions as to how this might have happened?

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