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• Why does C++ mandate that complex only be instantiated for float, double, or long double?

  - by templatetypedef

  According to the C++ ISO spec, §26.2/2: The effect of instantiating the template complex for any type other than float, double or long double is unspecified. Why would the standard authors explicitly add this restriction? This makes it unspecified, for example, what happens if you make complex<int> or a complex<MyCustomFixedPointType> and seems like an artificial restriction. Is there a reason for this limitation? Is there a workaround if you want to instantiate complex with your own custom type? I'm primarily asking this question because of this earlier question, in which the OP was confused as to why abs was giving bizarre outputs for complex<int>. That said, this still doesn't quite make sense given that we also might want to make complex numbers out of fixed-points types, higher-precision real numbers, etc. Thanks!

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• Better ways to print out column names when using cx_Oracle

  - by philipjkim

  Found an example using cx_Oracle, this example shows all the information of Cursor.description. import cx_Oracle from pprint import pprint connection = cx_Oracle.Connection("%s/%s@%s" % (dbuser, dbpasswd, oracle_sid)) cursor = cx_Oracle.Cursor(connection) sql = "SELECT * FROM your_table" cursor.execute(sql) data = cursor.fetchall() print "(name, type_code, display_size, internal_size, precision, scale, null_ok)" pprint(cursor.description) pprint(data) cursor.close() connection.close() What I wanted to see was the list of Cursor.description[0](name), so I changed the code: import cx_Oracle import pprint connection = cx_Oracle.Connection("%s/%s@%s" % (dbuser, dbpasswd, oracle_sid)) cursor = cx_Oracle.Cursor(connection) sql = "SELECT * FROM your_table" cursor.execute(sql) data = cursor.fetchall() col_names = [] for i in range(0, len(cursor.description)): col_names.append(cursor.description[i][0]) pp = pprint.PrettyPrinter(width=1024) pp.pprint(col_names) pp.pprint(data) cursor.close() connection.close() I think there will be better ways to print out the names of columns. Please get me alternatives to the Python beginner. :-)

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• BigInteger.ToString() returns more than 50 decimal digits.

  - by brickner

  I'm using .NET 4 System.Numerics.BigInteger Structure and I'm getting results different from the documentation. In the documentation of BigInteger.ToString() Method It says: The ToString() method supports 50 decimal digits of precision. That is, if the BigInteger value has more than 50 digits, only the 50 most significant digits are preserved in the output string; all other digits are replaced with zeros. I have some code that takes a 60 decimal digits BigInteger and converts it to a string. The 60 significant decimal digits string didn't lose any significant digits: const string vString = "123456789012345678901234567890123456789012345678901234567890"; Assert.AreEqual(60, vString.Length); BigInteger v = BigInteger.Parse(vString); Assert.AreEqual(60, v.ToString().Length); Assert.AreEqual('9', v.ToString()[58]); Assert.AreEqual('1', v.ToString()[0]); Assert.AreEqual(vString, v.ToString()); All the asserts pass. What exactly does the quoted part of the documentation mean?

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• How to split movie and play parts to look as a whole?

  - by luksow

  I'm writing software which is demonstraiting video on demand service. One of the feature is something similiar to IIS Smooth Streaming - I want to adjust quality to the bandwith of the client. My idea is, to split single movie into many, let's say - 2 seconds parts, in different qualities and then send it to the client and play them. The point is that for example first part can be in very high quality, and second in really poor (if the bandwith seems to be poor). The question is - do you know any software that allows me to cut movies precisly? For example ffmpeg splits movies in a way that join is visible and really annoying (seconds are the measure of precision). I use qt + phonon as a player if it matters. Or maybe you know any better way to provide such feature, without splitting movie into parts?

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• Do we ethically have the right to use the MAC Address for verification purposes?

  - by Matt Ridge

  I am writing a program, or starting at the very beginning of it, and I am thinking of purchase verification systems as a final step. I will be catering to Macs, PCs, and possibly Linux if all is said and done. I will also be programming this for smartphones as well using C++ and Objective-C. (I am writing a blueprint before going head first into it) That being said, I am not asking for help on doing it yet, but what I’m looking for is a realistic measurement for what could be expected as a viable and ethical option for purchase verification systems. Apple through the Apple Store, and some other stores out there have their own "You bought it" check. I am looking to use a three prong verification system. Email/password 16 to 32 character serial number using alpha/numeric and symbols with Upper and lowercase variants. MAC Address. The first two are in my mind ok, but I have to ask on an ethical standpoint, is a MAC Address to lock the software to said hardware unethical, or is it smart? I understand if an Ethernet card changes if not part of the logic board, or if the logic board changes so does the MAC address, so if that changes it will have to be re-verified, but I have to ask with how everything is today... Is it ethical to actually use the MAC address as a validation key or no? Should I be forward with this kind of verification system or should I keep it hidden as a secret? Yes I know hackers and others will find ways of knowing what I am doing, but in reality this is why I am asking. I know no verification is foolproof, but making it so that its harder to break is something I've always been interested in, and learning how to program is bringing up these questions, because I don't want to assume one thing and find out it's not really accepted in the programming world as a "you shouldn't do that" maneuver... Thanks in advance... I know this is my first programming question, but I am just learning how to program, and I am just making sure I'm not breaking some ethical programmer credo I shouldn't...

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• Mean of Sampleset and powered Sampleset

  - by Milla Well

  I am working on an ICA implementation wich is based on the assumption, that all source signals are independent. So I checked on the basic concepts of Dependence vs. Correlation and tried to show this example on sample data from numpy import * from numpy.random import * k = 1000 s = 10000 mn = 0 mnPow = 0 for i in arange(1,k): a = randn(s) a = a-mean(a) mn = mn + mean(a) mnPow = mnPow + mean(a**3) print "Mean X: ", mn/k print "Mean X^3: ", mnPow/k But I couldn't produce the last step of this example E(X^3) = 0: >> Mean X: -1.11174580826e-18 >> Mean X^3: -0.00125229267144 First value I would consider to be zero, but second value is too large, isn't it? Since I subtract the mean of a, I expected the mean of a^3 to be zero as well. Does the problem lie in the random number generator, the precision of the numerical values in my misunderstanding of the concepts of mean and expected value?

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• What language available on commodity web hosts would suit a C# developer? [closed]

  - by billpg

  Recognising its ubiquity on commodity web hosting services, I tried developing in PHP a few years ago. I really didn't like it, later deciding that life was too short for PHP. (In brief, having to put $ on variable names; mis-spelt variable names become new variables; converting non-numeric strings to integers without complaint; the need for an "and this time I mean it" comparison operator.) In my ideal world, commodity web hosts would all support C#/ASP.NET, my preferred web-development language and framework, but this is not my ideal world. Even Mono has barely made a dent on Linux based hosts. However, last time I moaned about PHP's ubiquity, someone followed up that this was no longer the case, and that many other languages are now commonly usable on web hosts too. What programming language; a. Would suit a developer who prefers C#. b. Is available to run on many web hosts.

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• F# powerpack and distribution

  - by rwallace

  I need arbitrary precision rational numbers, which I'm given to understand are available in the F# powerpack. My question is about the mechanics of distribution; my program needs to be able to compile and run both on Windows/.Net and Linux/Mono at least, since I have potential users on both platforms. As I understand it, the best procedure is: Download the powerpack .zip, not the installer. Copy the DLL into my program directory. Copy the accompanying license file into my program directory, to make sure everything is above board. Declare references and go ahead and use the functions I need. Ship the above files along with my source and binary, and since the DLL uses byte code, it will work fine on any platform. Is this the correct procedure? Am I missing anything?

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• Division inaccurate in Javascript?

  - by Nate

  If I perform the following operation in Javascript: 0.06120*400 The result is 24.48. However, if I do this: 24.48/400 The result is: 0.061200000000000004 JSFiddle: http://jsfiddle.net/zcDH7/ So it appears that Javascript rounds things differently when doing division and multiplication? Using my calculator, the operation 24.48/400 results in the correct answer of 0.0612. How should I deal with Javascript's inaccurate division? I can't simply round the number off, because I will be dealing with numbers of varying precision. Thanks for your advice.

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• Kernel module for /proc

  - by sb2367

  How to write a kernel module that creates a directory in /proc named mymod and a file in it name is mymodfile. This file should accept a number ranged from 1 to 3 when written into it and return the following messages when read based on the number already written into it: • 1: Current system time (in microseconds precision) • 2: System uptime • 3: Number of processes currently in the system “The Output” root@Paradise# echo 1 > /proc/mymod/mymodfile root@Paradise# cat /proc/mymod/mymodfile 08:30:24 342us root@Paradise# echo 2 > /proc/mymod/mymodfile root@Paradise# cat /proc/mymod/mymodfile up 1 day, 8 min root@Paradise# echo 3 > /proc/mymod/mymodfile root@Paradise# cat /proc/mymod/mymodfile process count: 48 please give me some hint how to write a kernel modules and how to compile and install it .

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• Why is this postgresql query so slow?

  - by user315975

  I'm no database expert, but I have enough knowledge to get myself into trouble, as is the case here. This query SELECT DISTINCT p.* FROM points p, areas a, contacts c WHERE ( p.latitude > 43.6511659465 AND p.latitude < 43.6711659465 AND p.longitude > -79.4677941889 AND p.longitude < -79.4477941889) AND p.resource_type = 'Contact' AND c.user_id = 6 is extremely slow. The points table has fewer than 2000 records, but it takes about 8 seconds to execute. There are indexes on the latitude and longitude columns. Removing the clause concering the resource_type and user_id make no difference. The latitude and longitude fields are both formatted as number(15,10) -- I need the precision for some calculations. There are many, many other queries in this project where points are compared, but no execution time problems. What's going on?

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• how to tesselate bezier triangles?

  - by Cheery

  My concern are quadratic bezier triangles which I'm trying to tesselate for rendering them. I've managed to implement this by subdividing the triangle recursively like described in a wikipedia page. Though I'd like to get more precision to subdivision. The problem is that I'll either get too few subdivisions or too many because the amount of surfaces doubles on every iteration of that algorithm. In particular I would need an adaptive tesselation algorithm that allows me to define the amount of segments at the edges. I'm not sure whether I can get that though so I'd also like to hear about uniform tesselation techniques. Hardest trouble I have trouble with calculating normals for a point in bezier surface, which I'm not sure whether I need, but been trying to solve out.

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• Convert long number as string in the serialization

  - by Bruno

  I have a custom made class that use a long as ID. However, when I call my action using ajax, my ID is truncated and it loses the last 2 numbers because javascript loses precision when dealing with large numbers. My solution would be to give a string to my javascript, but the ID have to stay as a long on the server side. Is there a way to serialize the property as a string? I'm looking for some kind of attribute. Controller public class CustomersController : ApiController { public IEnumerable<CustomerEntity> Get() { yield return new CustomerEntity() { ID = 1306270928525862486, Name = "Test" }; } } Model public class CustomerEntity { public long ID { get; set; } public string Name { get; set; } } JSON Result [{"Name":"Test","ID":1306270928525862400}]

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• How to very efficiently assign lat/long to city boundary described by shape ?

  - by watcherFR

  I have a huge shapefile of 36.000 non-overlapping polygones (city boundaries). I want to easily determine the polygone into which a given lat/long falls. What would the best way given that it must be extremely computationaly efficient ? I was thinking of creating a lookup table (tilex,tiley,polygone_id) where tilex and tiley are tile identifiers at zoom levels 21 or 22. Yes, the lack of precision of using tile numbers and a planar projection is acceptable in my application. I would rather not use postgres's GIS extension and am fine with a program that will run for 2 days to generate all the INSERT statements.

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• GSL interpolation error, values must be x values must be monotonically increasing

  - by pyCthon

  Hi my problem is that my data set is monotonically increasing but towards the end the of the data it looks like it does below ,where some of the x[i-1] = x[i] as shown below. This causes an error to be raised in GSL because it thinks that the values are not monotonically increasing. Is there a solution, fix or work around for this problem? the values are already double precision ,this particular data set starts at 9.86553e-06 and ends at .999999 would the only solution be to offset every value in a for loop? 0.999981 0.999981 0.999981 0.999982 0.999982 0.999983 0.999983 0.999983 0.999984 0.999984 0.999985 0.999985 0.999985

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• Merging similar graphs based solely on the graph structure?

  - by Buttons840

  I am looking for (or attempting to design) a technique for matching nodes from very similar graphs based on the structure of the graph*. In the examples below, the top graph has 5 nodes, and the bottom graph has 6 nodes. I would like to match the nodes from the top graph to the nodes in the bottom graph, such that the "0" nodes match, and the "1" nodes match, etc. This seems logically possible, because I can do it in my head for these simple examples. Now I just need to express my intuition in code. Are there any established algorithms or patterns I might consider? (* When I say based on the structure of the graph, I mean the solution shouldn't depend on the node labels; the numeric labels on the nodes are only for demonstration.) I'm also interested in the performance of any potential solutions. How well will they scale? Could I merge graphs with millions of nodes? In more complex cases, I recognize that the best solution may be subject to interpretation. Still, I'm hoping for a "good" way to merge complex graphs. (These are directed graphs; the thicker portion of an edge represents the head.)

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• Calculating the null space of a matrix

  - by Ainsworth

  I'm attempting to solve a set of equations of the form Ax = 0. A is known 6x6 matrix and I've written the below code using SVD to get the vector x which works to a certain extent. The answer is approximately correct but not good enough to be useful to me, how can I improve the precision of the calculation? Lowering eps below 1.e-4 causes the function to fail. from numpy.linalg import * from numpy import * A = matrix([[0.624010149127497 ,0.020915658603923 ,0.838082638087629 ,62.0778180312547 ,-0.336 ,0], [0.669649399820597 ,0.344105317421833 ,0.0543868015800246 ,49.0194290212841 ,-0.267 ,0], [0.473153758252885 ,0.366893577716959 ,0.924972565581684 ,186.071352614705 ,-1 ,0], [0.0759305208803158 ,0.356365401030535 ,0.126682113674883 ,175.292109352674 ,0 ,-5.201], [0.91160934274653 ,0.32447818779582 ,0.741382053883291 ,0.11536775372698 ,0 ,-0.034], [0.480860406786873 ,0.903499596111067 ,0.542581424762866 ,32.782593418975 ,0 ,-1]]) def null(A, eps=1e-3): u,s,vh = svd(A,full_matrices=1,compute_uv=1) null_space = compress(s <= eps, vh, axis=0) return null_space.T NS = null(A) print "Null space equals ",NS,"\n" print dot(A,NS)

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• All things equal what is the fastest way to output data to disk in C++?

  - by user260197

  I am running simulation code that is largely bound by CPU speed. I am not interested in pushing data in/out to a user interface, simply saving it to disk as it is computed. What would be the fastest solution that would reduce overhead? iostreams? printf? I have previously read that printf is faster. Will this depend on my code and is it impossible to get an answer without profiling? Edit: Output data needs to be in text format, whether tab or comma separated. This will require formatting, precision, etc. Running in Windows.

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• user height and weight in sql

  - by Samuel

  We are planning to capture a user's height and weight and am looking for ideas on representing them in sql. I have the following questions in mind weight can be expressed in kilograms and grams and height in meters and centimeters, so should I capture them as a BigDecimal with an appropriate precision and scale or capture them as vanilla strings and do the manipulation in the user interface. Note: I am planning to capture the kilograms and grams separately in the user interface. should the metric of measurement be part of the sql (i.e. the end user might want to view this information in pounds, inches according to his preference) OR Should I just support kilograms / meters in the database and do the conversion while showing this in the user interface

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• .Net Round-trip Types

  - by Fujiy

  I making a method that generate a unique string key for some parameters. But the same key if call with same values. I just accept primitive types, string, DateTime, Guid, and Nullable(since I append types together, I can distinguish who is int and who is int?), because I can convert all to string without lost values or precision.(for float and double a use ToString("R"), to DateTime ToString("O")). Exists a easy way to know which types I can transform in strings without conflict? And how do this transform(how I said before, float, double and datetime have specific ways) Thanks

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• Extracting useful information from free text

  - by insta

  We filter and analyse seats for events. Apparently writing a domain query language for the floor people isn't an option. I'm using C# 4.0 & .NET 4.0, and have relatively free reign to use whatever open-source tools are available. </background-info> If a request comes in for "FLOOR B", the sales people want it to show up if they've entered "FLOOR A-FLOOR F" in a filter. The only problem I have is that there's absolutely no structure to the parsed parameters. I get the string already concatenated (it actually uses a tilde instead of dash). Examples I've seen so far with matches after each: 101WC-199WC (needs to match 150WC) AAA-ZZZ (needs to match AAA, BBB, ABC but not BB) LOGE15-LOGE20 (needs to match LOGE15 but not LOGE150) At first I wanted to try just stripping off the numeric part of the lower and upper, and then incrementing through that. The problem I have is that only some entries have numbers, sometimes the numbers AND letters increment, sometimes its all letters that increment. Since I can't impose any kind of grammar to use (I really wanted [..] expansion syntax), I'm stuck using these entries. Are there any suggestions for how to approach this parsing problem?

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• Fluent NHibernate CheckProperty and Dates

  - by Chris C

  I setup a NUnit test as such: new PersistenceSpecification<MyTable>(_session) .CheckProperty(c => c.ActionDate, DateTime.Now); When I run the test via NUnit I get the following error: SomeNamespace.MapTest: System.ApplicationException : Expected '2/23/2010 11:08:38 AM' but got '2/23/2010 11:08:38 AM' for Property 'ActionDate' The ActionDate field is a datetime field in a SQL 2008 database. I use Auto Mapping and declare the ActionDate as a DateTime property in C#. If I change the test to use DateTime.Today the tests pass. My question is why is the test failing with DateTime.Now? Is NHibernate losing some precision when saving the date to the database and if so how do prevent the lose? Thank you.

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• C++ obtaining milliseconds time on Linux -- clock() doesn't seem to work properly

  - by hasen j

  On Windows, clock() returns the time in milliseconds, but on this Linux box I'm working on, it rounds it to the nearest 1000 so the precision is only to the "second" level and not to the milliseconds level. I found a solution with Qt using the QTime class, instantiating an object and calling start() on it then calling elapsed() to get the number of milliseconds elapsed. I got kind of lucky because I'm working with Qt to begin with, but I'd like a solution that doesn't rely on third party libraries, Is there no standard way to do this? UPDATE Please don't recommend Boost .. If Boost and Qt can do it, surely it's not magic, there must be something standard that they're using!

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• How do I prevent buffer overflow converting a double to char?

  - by Tommy

  I'm converting a double to a char string: char txt[10]; double num; num = 45.344322345 sprintf(txt, "%.1f", num); and using ".1f" to truncate the decimal places, to the tenths digit. i.e. - txt contains 45.3 I usually use precision in sprintf to ensure the char buffer is not overflowed. How can I do that here also truncating the decimal, without using snprintf? (i.e. if num = 345694876345.3 for some reason) Thanks

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• Convert Decimal number into Fraction

  - by alankrita

  I am trying to convert decimal number into its fraction. Decimal numbers will be having a maximum 4 digits after the decimal place. example:- 12.34 = 1234/100 12.3456 = 123456/10000 my code :- #include <stdio.h> int main(void) { double a=12.34; int c=10000; double b=(a-floor(a))*c; int d=(int)floor(a)*c+(int)b; while(1) { if(d%10==0) { d=d/10; c=c/10; } else break; } printf("%d/%d",d,c); return 0; } but I am not getting correct output, Decimal numbers will be of double precision only.Please guide me what I should do.

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