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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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• double returning only one precision in java

  - by srinath

  in my code i am performing division on numbers and storing it in a double variable. but the variable is returning with only one precision. i want to increase the precision how could i do that. double x; for ( int i =0 ; i<10000 ; i++) { x= w[i] / l[i]; System.out.println(x); } in the above code w and l are integer arrays; i am getting output like 3.0 0.0 1.0 0.0 i want to increase the precision upto 4 atleast.

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• only return random number when it is unique

  - by phil

  My brain is melting today and i cannot think how to do this simple bit of code. numberList is a string of numbers seperated by commas like '2, 34, 10' etc.. when i request a random number i need to check if the string has the number, if it does i want to keep requesting a random number until the random number is definitely not in the string. i cant think what kind of loop i would do to get this to work: Random r = new Random(); public int RandomPos(int max) { int i; do { i = r.Next(max) + 1; } while (!numberList.Contains(i.ToString())); return i; }

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• In Python, how do I search a flat file for the closest match to a particular numeric value?

  - by kaushik

  have file data of format 3.343445 1 3.54564 1 4.345535 1 2.453454 1 and so on upto 1000 lines and i have number given such as a=2.44443 for the given file i need to find the row number of the numbers in file which is most close to the given number "a" how can i do this i am presently doing by loading whole file into list and comparing each element and finding the closest one any other better faster method? my code:i need to ru this for different file each time around 20000 times so want a fast method p=os.path.join("c:/begpython/wavnk/",str(str(str(save_a[1]).replace('phone','text'))+'.pm')) x=open(p , 'r') for i in range(6): x.readline() j=0 o=[] for line in x: oj=str(str(line).rstrip('\n')).split(' ') o=o+[oj] j=j+1 temp=long(1232332) end_time=save_a[4] for i in range((j-1)): diff=float(o[i][0])-float(end_time) if diff<0: diff=diff*(-1) if temp>diff: temp=diff pm_row=i

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• Cache bandwidth per tick for modern CPUs

  - by osgx

  Hello What is a speed of cache accessing for modern CPUs? How many bytes can be read or written from memory every processor clock tick by Intel P4, Core2, Corei7, AMD? Please, answer with both theoretical (width of ld/sd unit with its throughput in uOPs/tick) and practical numbers (even memcpy speed tests, or STREAM benchmark), if any. PS it is question, related to maximal rate of load/store instructions in assembler. There can be theoretical rate of loading (all Instructions Per Tick are widest loads), but processor can give only part of such, a practical limit of loading.

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• Adding Timestamp to Java's GC messages in Tomcat 6

  - by ripper234

  I turned on Java's GC log options -XX:+PrintGC -XX:+PrintGCTimeStamps -XX:+PrintGCDetails Which print out these messages to standard output (catalina.out): 314.884: [CMS-concurrent-mark-start] 315.014: [CMS-concurrent-mark: 0.129/0.129 secs] [Times: user=0.14 sys=0.00, real=0.13 secs] 315.014: [CMS-concurrent-preclean-start] 315.016: [CMS-concurrent-preclean: 0.003/0.003 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 315.016: [CMS-concurrent-abortable-preclean-start] 332.055: [GC 332.055: [ParNew: 17128K->84K(19136K), 0.0017700 secs] 88000K->70956K(522176K) icms_dc=4 , 0.0018660 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] CMS: abort preclean due to time 352.253: [CMS-concurrent-abortable-preclean: 0.023/37.237 secs] [Times: user=0.78 sys=0.02, real=37.23 secs] How can I make these log lines appear with an actual timestamp (including date) instead of these numbers, which presumably mean "time since JVM started" ?

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• How do I find the millionth number in the series: 2 3 4 6 9 13 19 28 42 63 ... ?

  - by HH

  It takes about minute to achieve 3000 in my comp but I need to know the millionth number in the series. The definition is recursive so I cannot see any shortcuts except to calculate everything before the millionth number. How can you fast calculate millionth number in the series? Series Def n_{i+1} = \floor{ 3/2 * n_{i} } and n_{0}=2. Interestingly, only one site list the series according to Google: this one. Too slow Bash code #!/bin/bash function series { n=$( echo "3/2*$n" | bc -l | tr '\n' ' ' | sed -e 's@\\@@g' -e 's@ @@g' ); # bc gives \ at very large numbers, sed-tr for it n=$( echo $n/1 | bc ) #DUMMY FLOOR func } n=2 nth=1 while [ true ]; #$nth -lt 500 ]; do series $n # n gets new value in the function through global value echo $nth $n nth=$( echo $nth + 1 | bc ) #n++ done

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• Python code to do csv file row entries comparison operations and count the number of times row value

  - by Venomancer

  have an excel based CSV file with two columns (or rows, Pythonically) that I am working on. What I need to do is to perform some operations so that I can compare the two data entries in each 'row'. To be more precise, one column has constant numbers all the way down, whereas the other column has varying values. So I need to count the number of times the varying column data entry values crosses the constant value on the other column. For example, fro the csv file i have two columns: Varying Column; Constant Column 24 25 26 25 crossed 27 25 26 25 25.5 25 23 25 crossed 26 25 crossed Thus, the varying column data entries have crossed 25 three times. I need to generate a code that can count the number of the crosses. Please do help out, Thanks.

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• Write set of integers to std::ofstream and be able to read them back

  - by bndu

  Hello, I need to write a bunch of unsigned integers to std::ofstream in binary mode: std::ofstream f; f.open("some path", std::ios::out | std::ios::binary); // some loop { unsigned int k = get_k(); // may product numbers from 0 to 65535 f << k; } f.close(); They are written to the output file "as is" w/o any delimiter. So when I'm trying to read them back (expecting to get what I wrote) using std::ifstream I get very strange values. What I'm doing wrong? Or I should to put ' ' (space) to the stream after any added number to separate them? Thanks.

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• c++ - QListWidget

  - by user1889459

  I created a working QListWidget with multiple items, but I can't figure out how to make it user-friendly. It looks like this: 1000 1001 1002 ... But I want it to look like this, where firt 4 numbers have a meaning, while all the rest info is just for user. 1000 Name LastName and some other helpful info 1001 tom jeff smallville 1002 ming vase, 1992 ... For example, this line fotoId = ui->devices->currentItem()->text().toInt(); should give me same result in both cases.

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• When machine code is generated from a program how does it translates to hardware level operations ??

  - by user553492

  Like if say the instruction is something like 100010101 1010101 01010101 011101010101. Now how is this translating to an actual job of deleting something from memory? Memory consists of actual physical transistors the HOLD data. What causes them to lose that data is some external signal? I want to know how that signal is generated. Like how some binary numbers change the state of a physical transistor. Is there a level beyond machine code that isn't explicitly visible to a programmer? I have heard of microcode that handle code at hardware level, even below assembly language. But still I pretty much don't understand. Thanks!

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• Changing floating point behavior in Python to Numpy style.

  - by Tristan

  Is there a way to make Python floating point numbers follow numpy's rules regarding +/- Inf and NaN? For instance, making 1.0/0.0 = Inf. >>> from numpy import * >>> ones(1)/0 array([ Inf]) >>> 1.0/0.0 Traceback (most recent call last): File "<stdin>", line 1, in <module> ZeroDivisionError: float division Numpy's divide function divide(1.0,0.0)=Inf however it is not clear if it can be used similar to from __future__ import division.

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• Abort early in a fold

  - by Heptic

  What's the best way to terminate a fold early? As a simplified example, imagine I want to sum up the numbers in an Iterable, but if I encounter something I'm not expecting (say an odd number) I might want to terminate. This is a first approximation def sumEvenNumbers(nums: Iterable[Int]): Option[Int] = { nums.foldLeft (Some(0): Option[Int]) { case (None, _) => None case (Some(s), n) if n % 2 == 0 => Some(s + n) case (Some(_), _) => None } } However, this solution is pretty ugly (as in, if I did a .foreach and a return -- it'd be much cleaner and clearer) and worst of all, it traverses the entire iterable even if it encounters a non-even number. So what would be the best way to write a fold like this, that terminates early? Should I just go and write this recursively, or is there a more accepted way?

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• Should I Use GUID or IDENTITY as Thread Number?

  - by user311509

  offerID is the thread # which represents the thread posted. I see in forums posts are represented by random numbers. Is this achieved by IDENTITY? If not, please advice. nvarchar(max) will carry all kind of texts along with HTML tags. CREATE TABLE Offer ( offerID int IDENTITY (4382,15) PRIMARY KEY, memberID int NOT NULL REFERENCES Member(memberID), title nvarchar(200) NOT NULL, thread nvarchar(max) NOT NULL, . . . );

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• SQL Server concurrency and generated sequence

  - by Goyuix

  I need a sequence of numbers for an application, and I am hoping to leverage the abilities of SQL Server to do it. I have created the following table and procedure (in SQL Server 2005): CREATE TABLE sequences ( seq_name varchar(50) NOT NULL, seq_value int NOT NULL ) CREATE PROCEDURE nextval @seq_name varchar(50) AS BEGIN DECLARE @seq_value INT SET @seq_value = -1 UPDATE sequences SET @seq_value = seq_value = seq_value + 1 WHERE seq_name = @seq_name RETURN @seq_value END I am a little concerned that without locking the table/row another request could happen concurrently and end up returning the same number to another thread or client. This would be very bad obviously. Is this design safe in this regard? Is there something I can add that would add the necessary locking to make it safe? Note: I am aware of IDENTITY inserts in SQL Server - and that is not what I am looking for this in particular case. Specifically, I don't want to be inserting/deleting rows. This is basically to have a central table that manages the sequential number generator for a bunch of sequences.

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• how to set and access variable values from another classess

  - by BittenApple

  I am modifying QuartzDemo example app and want to do set and read values of integer type variables in other classes which are already included. For example, in MainViewController.m I want to set a numeric value (simple numbers from 1-100) to a variable which is then going to be called (read) in file QuartzImages.m. Question is how to define variable properly, set and access (read) the value. I am a beginner with Obj C and iPhone SDK in general and have some experience with Delphi and VB but this doesn't help at all :) Thank you, whoever and wherever you are, person who will take me out of this endless googling loop.

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• Remove parameter from link

  - by goordis

  I have many links with parameter number - value is numbers between 1-1000 http://mysite.com?one=2&two=4&number=2 http://mysite.com?one=2&two=4&four=4&number=124 http://mysite.com?one=2&three=4&number=9 http://mysite.com?two=4&number=242 http://mysite.com?one=2&two=4&number=52 How can i remove from this parameter and value with PHP? I would like receive: http://mysite.com?one=2&two=4 http://mysite.com?one=2&two=4&four=4 http://mysite.com?one=2&three=4 http://mysite.com?two=4 http://mysite.com?one=2&two=4

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• add/delete image ID to/from textbox when image clicked

  - by Huseyin

  I am working on a simple news module. There is a form where user adds multiple image IDs to one textbox then submits it. To improve the usability, I listed all the images they can add (ID numbers displayed next to it) on one side. However, this still is little bit confusing. I want image IDs added/deleted to the textbox when user clicks on the images. Spare me codes, methods, ideas, examples... I will take anything.

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• Generating Fibonacci series in F#

  - by photo_tom

  I'm just starting to learn F# using VS2010 and below is my first attempt at generating the Fibonacci series. What I'm trying to do is to build a list of all numbers less than 400. let fabList = let l = [1;2;] let mutable a = 1 let mutable b = 2 while l.Tail < 400 do let c = a + b l.Add(c) let a = b let b = c My first problem is that on the last statement, I'm getting an error message "Incomplete structured construct at or before this point in expression" on the last line. I don't understand what I'm doing wrong here. While this seems to be an obvious way to build the list in a fairly efficient way (from a c++/C# programmer), from what little I know of f#, this doesn't seem to feel to be the right way to do the program. Am I correct in this feeling?

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• What is the cost of memory access?

  - by Jurily

  We like to think that a memory access is fast and constant, but on modern architectures/OSes, that's not necessarily true. Consider the following C code: int i = 34; int *p = &i; // do something that may or may not involve i and p {...} // 3 days later: *p = 643; What is the estimated cost of this last assignment in CPU instructions, if i is in L1 cache, i is in L2 cache, i is in L3 cache, i is in RAM proper, i is paged out to an SSD disk, i is paged out to a traditional disk? Where else can i be? Of course the numbers are not absolute, but I'm only interested in orders of magnitude. I tried searching the webs, but Google did not bless me this time.

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• Which database should I use for best performance

  - by _simon_

  Hello, I am working in Visual Studio 2005, .NET 2.0. I need to write an application, which listens on COM port and saves incoming data to a database. Main feature: save incoming data (series of 13-digits numbers), if this number allready exists, then mark it as double. For example, there could be these records in database: 0000000000001 OK 0000000000002 OK 0000000000002 Double 0000000000003 OK 0000000000004 OK I could use SQL database, but I don't know if it is fast enough... Database should be able to store up to 10.000.000 records and write up to 100 records per minute (so it needs to check 100 times per minute if this record allready exists). Which database should I use? Maybe the whole database would need to be in RAM. Where could I learn more about this? Thanks

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• Finding number of different paths

  - by peiska

  I have a game that one player X wants to pass a ball to player Y, but he can be playing with more than one player and the others players can pass the ball to Y. I want to know how many different paths can the ball take from X to Y? for example if he is playing with 3 players there are 5 different paths, 4 players 16 paths, if he is playing with 20 players there are 330665665962404000 paths, and 40 players 55447192200369381342665835466328897344361743780 that the ball can take. the number max. of players that he can play with is 500. I was thinking in using Catalan Numbers? do you think is a correct approach to solve this? Can you give me some tips.

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• How to check input text into web form? java script

  - by butteff

  how to check input text before POST operation? it must be numbers only <form method="post" action="credit.php"> ????? ???????: <input type="text" name="sum"> <br /> ?????? ?????: <input type="text" name="pv"> <br /> ????: <input type="text" name="srok"> <br /> ?????????? ??????: <input type="text" name="percent"> <br /> <input type="submit"> </form> sorry for my bad english.

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• Python - a clean approach to this problem?

  - by Seafoid

  Hi, I am having trouble picking the best data structure for solving a problem. The problem is as below: I have a nested list of identity codes where the sublists are of varying length. li = [['abc', 'ghi', 'lmn'], ['kop'], ['hgi', 'ghy']] I have a file with two entries on each line; an identity code and a number. abc 2.93 ghi 3.87 lmn 5.96 Each sublist represents a cluster. I wish to select the i.d. from each sublist with the highest number associated with it, append that i.d. to a new list and ultimately write it to a new file. What data structure should the file with numbers be read in as? Also, how would you iterate over said data structure to return the i.d. with the highest number that matches the i.d. within a sublist? Thanks, S :-)

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• Importing data from a text file using python

  - by Will

  I have a text file containing data in rows and columns (~17000 rows in total). Each column is a uniform number of characters long, with the 'unused' characters filled in by spaces. For example, the first column is 11 characters long, but the last four characters in that column are always spaces (so that it appears to be a nice column when viewed with a text editor). Sometimes it's more than four if the entry is less than 7 characters. The columns are not otherwise separated by commas, tabs, or spaces. They are also not all the same number of characters (the first two are 11, the next two are 8 and the last one is 5 - but again, some are spaces). What I want to do is import the entires (which are numbers) in the last two columns if the second column contains the string 'OW' somewhere in it. Any help would be greatly appreciated.

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