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  • Guidance in naming awkward objects?

    - by GlenH7
    I'm modeling a chemical system, and I'm having problems with naming my objects within an enum. I'm not sure if I should use: the atomic formula the chemical name an abbreviated chemical name. For example, sulfuric acid is H2SO4 and hydrochloric acid is HCl. With those two, I would probably just use the atomic formula as they are reasonably common. However, I have others like sodium hexafluorosilicate which is Na2SiF6. In that example, the atomic formula isn't as obvious (to me) but the chemical name is hideously long: myEnum.SodiumHexaFluoroSilicate. I'm not sure how I would be able to safely come up with an abbreviated chemical name that would have a consistent naming pattern. From a maintenance point of view, which of the options would you prefer to see and why? Audience for the code will be just programmers, not chemists. If that guides the particulars: I'm using C#; I'm starting with 10 - 20 compounds and would have at most 100 compounds. The enum is to facilitate common calculations - the equation is the same for all compounds but you insert a property of the compound to complete the equation.

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  • Guidance in naming awkward domain-specific objects?

    - by GlenH7
    I'm modeling a chemical system, and I'm having problems with naming my objects within an enum. I'm not sure if I should use: the atomic formula the chemical name an abbreviated chemical name. For example, sulfuric acid is H2SO4 and hydrochloric acid is HCl. With those two, I would probably just use the atomic formula as they are reasonably common. However, I have others like sodium hexafluorosilicate which is Na2SiF6. In that example, the atomic formula isn't as obvious (to me) but the chemical name is hideously long: myEnum.SodiumHexaFluoroSilicate. I'm not sure how I would be able to safely come up with an abbreviated chemical name that would have a consistent naming pattern. From a maintenance point of view, which of the options would you prefer to see and why? Some details from comments on this question: Audience for the code will be just programmers, not chemists. I'm using C#, but I think this question is more interesting when ignoring the implementation language I'm starting with 10 - 20 compounds and would have at most 100 compounds. The enum is to facilitate common calculations - the equation is the same for all compounds but you insert a property of the compound to complete the equation. For example, Molar mass (in g/mol) is used when calculating the number of moles from a mass (in grams) of the compound. Another example of a common calculation is the Ideal Gas Law and its use of the Specific Gas Constant

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  • single for-loop runtime explanation problem

    - by owwyess
    I am analyzing some running times of different for-loops, and as I'm getting more knowledge, I'm curious to understand this problem which I have still yet to find out. I have this exercise called "How many stars are printed": for (int i = N; i > 1; i = i/2) System.out.println("*"); The answers to pick from is A: ~log N B: ~N C: ~N log N D: ~0.5N^2 So the answer should be A and I agree to that, but on the other side.. Let's say N = 500 what would Log N then be? It would be 2.7. So what if we say that N=500 on our exercise above? That would most definitely print more han 2.7 stars? How is that related? Because it makes sense to say that if the for-loop looked like this: for (int i = 0; i < N; i++) it would print N stars. I hope to find an explanation for this here, maybe I'm interpreting all these things wrong and thinking about it in a bad way. Thanks in advance.

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  • How to force a clock update using ntp?

    - by ysap
    I am running Ubuntu on an ARM based embedded system that lacks a battery backed RTC. The wake-up time is somewhere during 1970. Thus, I use the NTP service to update the time to the current time. I added the following line to /etc/rc.local file: sudo ntpdate -s time.nist.gov However, after startup, it still takes a couple of minutes until the time is updated, during which period I cannot work effectively with tar and make. How can I force a clock update at any given time? UPDATE 1: The following (thanks to Eric and Stephan) works fine from command line, but fails to update the clock when put in /etc/rc.local: $ date ; sudo service ntp stop ; sudo ntpdate -s time.nist.gov ; sudo service ntp start ; date Thu Jan 1 00:00:58 UTC 1970 * Stopping NTP server ntpd [ OK ] * Starting NTP server [ OK ] Thu Feb 14 18:52:21 UTC 2013 What am I doing wrong? UPDATE 2: I tried following the few suggestions that came in response to the 1st update, but nothing seems to actually do the job as required. Here's what I tried: Replace the server to us.pool.ntp.org Use explicit paths to the programs Remove the ntp service altogether and leave just sudo ntpdate ... in rc.local Remove the sudo from the above command in rc.local Using the above, the machine still starts at 1970. However, when doing this from command line once logged in (via ssh), the clock gets updated as soon as I invoke ntpdate. Last thing I did was to remove that from rc.local and place a call to ntpdate in my .bashrc file. This does update the clock as expected, and I get the true current time once the command prompt is available. However, this means that if the machine is turned on and no user is logged in, then the time never gets updates. I can, of course, reinstall the ntp service so at least the clock is updated within a few minutes from startup, but then we're back at square 1. So, is there a reason why placing the ntpdate command in rc.local does not perform the required task, while doing so in .bashrc works fine?

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  • Is there a common programming term for the problems of adding features to an already-featureful program?

    - by Jeremy Friesner
    I'm looking for a commonly used programming term to describe a software-engineering phenomenon, which (for lack of a better way to describe it) I'll illustrate first with a couple of examples-by-analogy: Scenario 1: We want to build/extend a subway system on the outskirts of a small town in Wyoming. There are the usual subway-problems to solve, of course (hiring the right construction company, choosing the best route, buying the subway cars), but other than that it's pretty straightforward to implement the system because there aren't a huge number of constraints to satisfy. Scenario 2: Same as above, except now we need to build/extend the subway system in downtown Los Angeles. Here we face all of the problems we did in case (1), but also additional problems -- most of the applicable space is already in use, and has a vocal constituency which will protest loudly if we inconvenience them by repurposing, redesigning, or otherwise modifying the infrastructure that they rely on. Because of this, extensions to the system happen either very slowly and expensively, or they don't happen at all. I sometimes see a similar pattern with software development -- adding a new feature to a small/simple program is straightforward, but as the program grows, adding further new features becomes more and more difficult, if only because it is difficult to integrate the new feature without adversely affecting any of the large number of existing use-cases or user-constituencies. (even with a robust, adaptable program design, you run into the problem of the user interface becoming so elaborate that the program becomes difficult to learn or use) Is there a term for this phenomenon?

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  • Too complex/too many objects?

    - by Mike Fairhurst
    I know that this will be a difficult question to answer without context, but hopefully there are at least some good guidelines to share on this. The questions are at the bottom if you want to skip the details. Most are about OOP in general. Begin context. I am a jr dev on a PHP application, and in general the devs I work with consider themselves to use many more OO concepts than most PHP devs. Still, in my research on clean code I have read about so many ways of using OO features to make code flexible, powerful, expressive, testable, etc. that is just plain not in use here. The current strongly OO API that I've proposed is being called too complex, even though it is trivial to implement. The problem I'm solving is that our permission checks are done via a message object (my API, they wanted to use arrays of constants) and the message object does not hold the validation object accountable for checking all provided data. Metaphorically, if your perm containing 'allowable' and 'rare but disallowed' is sent into a validator, the validator may not know to look for 'rare but disallowed', but approve 'allowable', which will actually approve the whole perm check. We have like 11 validators, too many to easily track at such minute detail. So I proposed an AtomicPermission class. To fix the previous example, the perm would instead contain two atomic permissions, one wrapping 'allowable' and the other wrapping 'rare but disallowed'. Where previously the validator would say 'the check is OK because it contains allowable,' now it would instead say '"allowable" is ok', at which point the check ends...and the check fails, because 'rare but disallowed' was not specifically okay-ed. The implementation is just 4 trivial objects, and rewriting a 10 line function into a 15 line function. abstract class PermissionAtom { public function allow(); // maybe deny() as well public function wasAllowed(); } class PermissionField extends PermissionAtom { public function getName(); public function getValue(); } class PermissionIdentifier extends PermissionAtom { public function getIdentifier(); } class PermissionAction extends PermissionAtom { public function getType(); } They say that this is 'not going to get us anything important' and it is 'too complex' and 'will be difficult for new developers to pick up.' I respectfully disagree, and there I end my context to begin the broader questions. So the question is about my OOP, are there any guidelines I should know: is this too complicated/too much OOP? Not that I expect to get more than 'it depends, I'd have to see if...' when is OO abstraction too much? when is OO abstraction too little? how can I determine when I am overthinking a problem vs fixing one? how can I determine when I am adding bad code to a bad project? how can I pitch these APIs? I feel the other devs would just rather say 'its too complicated' than ask 'can you explain it?' whenever I suggest a new class.

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  • Finding the median of the merged array of two sorted arrays in O(logN)?

    - by user176517
    Refering to the solution present at MIT handout I have tried to figure out the solution myself but have got stuck and I believe I need help to understand the following points. In the function header used in the solution MEDIAN -SEARCH (A[1 . . l], B[1 . . m], max(1,n/2 - m), min(l, n/2)) I do not understand the last two arguments why not simply 1, l why the max and min respectively. Thanking You.

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  • Best way to restore individual folders via Time Machine after clean Lion install?

    - by A4J
    I'm doing a clean erase and install of Lion, and am looking for the best way to restore individual folders into my home directory via Time Machine. I've done a dummy run, clean Lion install, then 'browse other disks' in Time Machine, navigate to my home folder and 'restore' what I need, such as pictures/music and folders inside the .library folder (such as Mail and Keychains). However this method seems to give you odd permissions, like this: http://i43.tinypic.com/15y82v4.png Hence I wondered if anyone knows what the best method is to restore files and folders after a clean install. N.b I do not want to use the migration assistant, or 'restore OS from Time Machine' - as I specifically want to do a clean install, and just copy over what I need (some folders will be moved onto a separate disk to the OS, and some will remain on the same disk). Thanks in advance.

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  • Is it reasonable to use my Time Machine backup to migrate to a new primary hard drive?

    - by Michael Haren
    I'm planning to upgrade my MacBook's harddrive. I already use Time Machine to back up the system to an external drive. Is it reasonable to use Time Machine to restore my system to the new laptop drive, once I install it? I mean, a restore like this really ought to be fine, right? That's the point of it, after all! I know imaging the drive would be more appropriate but this plan seems a whole lot easier (albeit probably slower), with practically no risk since my original drive won't be involved. A second question would then be, are there any considerations to be made when doing a Time Machine restore?

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  • Is an Ethernet point to point connection without a switch real time capable?

    - by funksoulbrother
    In automation and control, it is commonly stated that ethernet can't be used as a bus because it is not real time capable due to packet collisions. If important control packets collide, they often can't keep the hard real time conditions needed for control. But what if I have a single point to point connection with Ethernet, no switch in between? To be more precise, I have an FPGA board with a giga-Ethernet port that is connected directly to my control PC. I think the benefits of giga Ethernet over CAN or USB for a p2p connection are huge, especially for high sampling rates and lots of data generation on the FPGA board. Am I correct that with a point to point connection there can't be any packet collisions and therefore a real time environment is given even with ethernet? Thanks in advance! ~fsb

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  • How to reuse backup on Time Machine on Snow Leopard after a logic board change, after choosing wrong

    - by kmiffy
    After my logic board was replaced, I connected my laptop back to my network, and Time Machine gave me a popup, as shown on this thread: http://superuser.com/questions/78068/recycle-time-machine-for-new-machine/78264#78264 I misread the question and clicked on "Create New Backup" when I should have clicked on "Reuse Backup" to connect to my old backup file. How can I trigger that popup again? Turning Time Machine on and off does not work, and the instructions on forums to fix via terminal doesn't work because snow leopard is missing the fsaclctl command (and I'm also not familiar with terminal commands.) Thanks.

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  • Is there any software or hardware which lets you stop, slow down, speed up or even reverse time?

    - by tjrobinson
    Obviously I'm talking about time in terms of the PC clock rather than real time. We were testing an application we've developed at work by setting the clock forward and back to simulate different scenarios and I started thinking how useful it would be if you could adjust the rate(?) of the system clock with finer control. So you could make a minute pass in a second or a day pass in 30 seconds and watch how the program you're developing copes with changes in date and time. I'd be interested to hear if anyone knows of any software or hardware which can let you do some or all of the above.

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  • What is normal SCSI error handling process (scsi_eh_3) CPU time usage?

    - by Kris Jordan
    Last week I got setup with a new dedicated server that is running 4x SCSI drives in RAID 10 on CentOS. The machine is pretty lightly loaded at the moment and has been running for 8 days. The process 'scsi_eh_3' has a CPU time of 13:09.67 in top. This is 3x the next closest CPU time of 4:03.93 for mysqld. Is it normal for the scsi error handling process to use this much CPU time? (Seems like it goes to 0.3% usage ever 5 seconds.) Could this be an indicator that one or more of the drives is having issues?

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  • Is it safe to change the time on hosting VM server?

    - by hydroparadise
    So, I noticed there's about a 10 minute drift on my VM hosting server from what time it's supposed to be. In traditional environments, I would just restart the system (and change the BIOS time if necassary). The hosting server is Ubuntu 12.04. Undertsanding that some process could be time sensitive (NTP?), I was wondering how this might affect the relation between the host and hosted system (currently hosting 4: 3 Ubuntu 12.04 servers with one being a web server, and 1 Windows Server 2008 file server). I am using Virtual Box 4 with it's headless option. Ultimately, I am trying to avoid from shutting down the host (which ultimately mean shutthing down the other hosted systems). Is this safe?

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  • Monitoring the wall time of a process on windows?

    - by Sean Madden
    Windows Task Manager has the ability to show the current CPU time of any given running process on windows, is there any way (not necessarily through Task Manager) to get the current wall time of a process? An example, let's say I have a script that reliably runs for about 45 minutes. Without adding a progress bar to the script, is there any way to figure out for how long it has been running? The math behind this seems pretty straight forward; WallTime = CurrentWallTime - WallTimeProcessStarted. Likewise, since the math is so simple, is there anyway to get the time that a process was started at?

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  • Is there a time machine equivalent for windows that can back up network files?

    - by Jim Thio
    This question is similar to Does an equivalent of Time Machine exist for Windows?, with one difference: The files I want to back up are on a network drive. The computer on that network drive is running Windows XP. I want to back up data on Windows 7. How would I do so? I'd like something similar to Mac OS X' time machine. So copy of data every hour, day, week. Then thinning out, data gets deleted automatically as time goes by. For example, the data for last day is kept as hourly snapshots. For last week, as daily snapshots every day. And for last month as weekly snapshots. How can I achieve this?

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  • Cloud storage services offering one-time download links? [closed]

    - by TARehman
    Is anyone aware of consumer-targeted cloud storage services that allow users to generate a one-time download link for hosted files? Case in point: I have an encrypted container with some documents I need to send to a vendor. I would prefer to give them a one-time download link, so that I know when they have accessed the file, and then inform them of the passphrase by phone. I have heard that MediaFire offers 1-time links, but that they are buried in tons of advertising. At the moment, I'm not sure that I consider MediaFire fully legitimate; I'm more interested in solutions with Google Drive, Box.net, DropBox, etc.

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  • SQL SERVER – Get Date and Time From Current DateTime – SQL in Sixty Seconds #025 – Video

    - by pinaldave
    This is 25th video of series SQL in Sixty Seconds we started a few months ago. Even though this is 25th video it seems like we have just started this few days ago. The best part of this SQL in Sixty Seconds is that one can learn something new in less than sixty seconds. There are many concepts which are not new for many but just we all have 60 seconds to refresh our memories. In this video I have touched a very simple question which I receive very frequently on this blog. Q1) How to get current date time? Q2) How to get Only Date from datetime? Q3) How to get Only Time from datetime? I have created a sixty second video on this subject and hopefully this will help many beginners in the SQL Server field. This sixty second video describes the same. Here is a similar script which I have used in the video. SELECT GETDATE() GO -- SQL Server 2000/2005 SELECT CONVERT(VARCHAR(8),GETDATE(),108) AS HourMinuteSecond, CONVERT(VARCHAR(8),GETDATE(),101) AS DateOnly; GO -- SQL Server 2008 Onwards SELECT CONVERT(TIME,GETDATE()) AS HourMinuteSeconds; SELECT CONVERT(DATE,GETDATE()) AS DateOnly; GO Related Tips in SQL in Sixty Seconds: Retrieve Current Date Time in SQL Server CURRENT_TIMESTAMP, GETDATE(), {fn NOW()} Get Time in Hour:Minute Format from a Datetime – Get Date Part Only from Datetime Get Current System Date Time Get Date Time in Any Format – UDF – User Defined Functions Date and Time Functions – EOMONTH() – A Quick Introduction DATE and TIME in SQL Server 2008 I encourage you to submit your ideas for SQL in Sixty Seconds. We will try to accommodate as many as we can. If we like your idea we promise to share with you educational material. Image Credit: Movie Gone in 60 Seconds Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Server Management Studio, SQL Tips and Tricks, T SQL, Technology, Video

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  • Advice for Storing and Displaying Dates and Times Across Different Time Zones

    A common question I receive from clients, colleagues, and 4Guys readers is for recommendations on how best to store and display dates and times in a data-driven web application. One of the challenges in storing and displaying dates in a web application is that it is quite likely that the visitors arriving at your site are not in the same time zone as your web server; moreover, it's very likely that your site attracts visitors from many different time zones from around the world. Consider an online messageboard site, like ASPMessageboard.com, where each of 1,000,000+ posts includes the date and time it was made. Imagine a user from New York leaves a post on April 7th at 4:30 PM and that the web server hosting the site is located in Dallas, Texas, which is one hour earlier than New York. When storing that post to the database do you record the post's date and time relative to the visitor (4:30 PM), the relative to the web server (3:30 PM), or some other value? And when displaying this post how do you show that date and time to a reader in San Francisco, which is three hours earlier than New York? Do you show the time relative to the person who made the post (4:30 PM), relative to the web server (3:30 PM), or relative to the user (1:30 PM)? And if you decide to store or display the date based on the poster's or visitor's time zone then how do you know their time zone and its offset? How do you account for daylight savings, and so on? This article provides guidance on how to store and display dates and times for visitors across different time zones and includes a demo that gives a working example of some of these techniques. Read on to learn more! Read More >

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  • Getting time in ubuntu

    - by user2578666
    include #include <stdio.h> int GetTime() { struct timespec tsp; clock_gettime(CLOCK_REALTIME, &tsp); //Call clock_gettime to fill tsp fprintf(stdout, "time=%d.%d\n", tsp.tv_sec, tsp.tv_nsec); fflush(stdout); } I am trying to compile the above code but it keeps throwing the error: time.c: In function ‘GetTime’: time.c:12:4: warning: implicit declaration of function ‘clock_gettime’ [-Wimplicit-function-declaration] time.c:12:18: error: ‘CLOCK_REALTIME’ undeclared (first use in this function) time.c:12:18: note: each undeclared identifier is reported only once for each function it appears in time.c:14:4: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘__time_t’ [-Wformat] time.c:14:4: warning: format ‘%d’ expects argument of type ‘int’, but argument 4 has type ‘long int’ [-Wformat] I have tried compiling with -lrt flag and -std=gnu99. Nothing works.

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  • A lot of TCP: time wait bucket table overflow in CentOS 6

    - by divaka
    we have the following output from dmesg: __ratelimit: 33491 callbacks suppressed TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow TCP: time wait bucket table overflow Also we have the following setting: cat /proc/sys/net/ipv4/tcp_max_tw_buckets 524288 We are under some kind of attack, but we could not detect what cause this problem?

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  • Sort vector<int>(n) in O(n) time using O(m) space?

    - by Adam
    I have a vector<unsigned int> vec of size n. Each element in vec is in the range [0, m], no duplicates, and I want to sort vec. Is it possible to do better than O(n log n) time if you're allowed to use O(m) space? In the average case m is much larger than n, in the worst case m == n. Ideally I want something O(n). I get the feeling that there's a bucket sort-ish way to do this: unsigned int aux[m]; aux[vec[i]] = i; Somehow extract the permutation and permute vec. I'm stuck on how to do 3. In my application m is on the order of 16k. However this sort is in the inner loops and accounts for a significant portion of my runtime.

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