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  • How do I make this nested for loop, testing sums of cubes, more efficient?

    - by Brian J. Fink
    I'm trying to iterate through all the combinations of pairs of positive long integers in Java and testing the sum of their cubes to discover if it's a Fibonacci number. I'm currently doing this by using the value of the outer loop variable as the inner loop's upper limit, with the effect being that the outer loop runs a little slower each time. Initially it appeared to run very quickly--I was up to 10 digits within minutes. But now after 2 full days of continuous execution, I'm only somewhere in the middle range of 15 digits. At this rate it may end up taking a whole year just to finish running this program. The code for the program is below: import java.lang.*; import java.math.*; public class FindFib { public static void main(String args[]) { long uLimit=9223372036854775807L; //long maximum value BigDecimal PHI=new BigDecimal(1D+Math.sqrt(5D)/2D); //Golden Ratio for(long a=1;a<=uLimit;a++) //Outer Loop, 1 to maximum for(long b=1;b<=a;b++) //Inner Loop, 1 to current outer { //Cube the numbers and add BigDecimal c=BigDecimal.valueOf(a).pow(3).add(BigDecimal.valueOf(b).pow(3)); System.out.print(c+" "); //Output result //Upper and lower limits of interval for Mobius test: [c*PHI-1/c,c*PHI+1/c] BigDecimal d=c.multiply(PHI).subtract(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)), e=c.multiply(PHI).add(BigDecimal.ONE.divide(c,BigDecimal.ROUND_HALF_UP)); //Mobius test: if integer in interval (floor values unequal) Fibonacci number! if (d.toBigInteger().compareTo(e.toBigInteger())!=0) System.out.println(); //Line feed else System.out.print("\r"); //Carriage return instead } //Display final message System.out.println("\rDone. "); } } Now the use of BigDecimal and BigInteger was delibrate; I need them to get the necessary precision. Is there anything other than my variable types that I could change to gain better efficiency?

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  • How to write efficient code for extracting Noun phrases?

    - by Arun Abraham
    I am trying to extract phrases using rules such as the ones mentioned below on text which has been POS tagged 1) NNP - NNP (- indicates followed by) 2) NNP - CC - NNP 3) VP - NP etc.. I have written code in this manner, Can someone tell me how i can do in a better manner. List<String> nounPhrases = new ArrayList<String>(); for (List<HasWord> sentence : documentPreprocessor) { //System.out.println(sentence.toString()); System.out.println(Sentence.listToString(sentence, false)); List<TaggedWord> tSentence = tagger.tagSentence(sentence); String lastTag = null, lastWord = null; for (TaggedWord taggedWord : tSentence) { if (lastTag != null && taggedWord.tag().equalsIgnoreCase("NNP") && lastTag.equalsIgnoreCase("NNP")) { nounPhrases.add(taggedWord.word() + " " + lastWord); //System.out.println(taggedWord.word() + " " + lastWord); } lastTag = taggedWord.tag(); lastWord = taggedWord.word(); } } In the above code, i have done only for NNP followed by NNP extraction, how can i generalise it so that i can add other rules too. I know that there are libraries available for doing this , but wanted to do this manually.

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  • Is it possible to create an efficient UDF alternative to Excel's CUBEVALUE function?

    - by bright
    We'd like to create a simpler alternative to Excel's CUBEVALUE function for retrieving data from an OLAP server. The details aren't critical, but briefly, our function will "know" the source connection and accept a very simple ticker-like parameter and a date, in place of CUBEVALUE's MDX-style parameters. This is for internal use within our firm, just FYI. However, Excel has optimized CUBEVALUE so that calls to the OLAP server are batched. Question: Is there a way to code the new function so that it can similarly batch calls rather than issue a separate query for each cell?

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  • Which is more efficient/faster when calling a cached image?

    - by andufo
    Hi, i made an image resizer in php. When an image is resized, it caches a new jpg file with the new dimensions. Next time you call the exact img.php?file=hello.jpg&size=400 it checks if the new jpg has already been created. If it has NOT been created yet, it creates the file and then prints the output (cool). If it ALREADY exists, no new file needs to be generated and instead, it just calls the already cached file. My question is regarding the second scenario. Which of these is faster? redirecting: header('Location: cache/hello_400.jpg');die(); grabbing data and printing the cached file: $data = file_get_contents('cache/hello_400.jpg'); header('Content-type: '.$mime); header('Content-Length: '.strlen($data)); echo $data; Any other ways to improve this?

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  • What is the most efficient way to get the highest and the lowest values in a Array

    - by meo
    is there something like PHP: max() in javascript? lets say i have an array like this: [2, 3, 23, 2, 2345, 4, 86, 8, 231, 75] and i want to return the highest and the lowest value in this array. What is the fastest way to do that? i have tried: function madmax (arr) { var max = arr[0], min = arr[1] if (min > max) { max = arr[1] min = arr[0] } for (i=1;i<=arr.length;i++){ if( arr[i] > max ) { max = arr[i] }else if( arr[i] < min ) { min = arr[i] } } return max, min } madmax([123, 2, 345, 153, 5, 98, 456, 4323456, 1, 234, 19874, 238, 4]) Is there a simpler way retrieve the max and min value of a array?

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  • Is there a module that implements an efficient array type in Erlang?

    - by dsmith
    I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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  • What is the most efficient way to learn x86 assembly?

    - by Web Des
    I want to learn x86 assembly and I want to know if learning reverse engineering is a good way to learn it? Also I have some c++ knowledge of pointers, stack, heap , references, etc.. I was considering this book. http://www.amazon.com/Reversing-Secrets-Engineering-Eldad-Eilam/dp/0764574817/ref=sr_1_1?s=books&ie=UTF8&qid=1340420512&sr=1-1&keywords=reverse+engineering Also Is reverse engineering the same as what they call disassembly?

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  • How do I make this Query against EF Efficient?

    - by dudeNumber4
    Using EF4. Assume I have this: IQueryable<ParentEntity> qry = myRepository.GetParentEntities(); Int32 n = 1; What I want to do is this, but EF can't compare against null. qry.Where( parent => parent.Children.Where( child => child.IntCol == n ) != null ) What works is this, but the SQL it produces (as you would imagine) is pretty inefficient: qry.Where( parent => parent.Children.Where( child => child.IntCol == n ).FirstOrDefault().IntCol == n ) How can I do something like the first comparison to null that won't be generating nested queries and so forth?

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  • What is the most efficient way to encode an arbitrary GUID into readable ASCII (33-127)?

    - by mark
    Dear ladies and sirs. The standard string representation of GUID takes about 36 characters. Which is very nice, but also really wasteful. I am wondering, how to encode it in the shortest possible way using all the ASCII characters in the range 33-127. The naive implementation produces 22 characters, simply because 128 bits / 6 bits yields 22. Huffman encoding is my second best, the only question is how to choose the codes.... Any more ideas? Thanks. P.S. The encoding must be lossless, of course.

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  • "Single NSMutableArray" vs. "Multiple C-arrays" --Which is more Efficient/Practical?

    - by RexOnRoids
    Situation: I have a DAY structure. The DAY structure has three variables or attributes: a Date (NSString*), a Temperature (float), and a Rainfall (float). Problem: I will be iterating through an array of about 5000 DAY structures and graphing a portion of these onto the screen using OpenGL. Question: As far as drawing performance, which is better? I could simply create an NSMutableArray of DAY structures (NSObjects) and iterate on the array on each draw call -- which I think would be hard on the CPU. Or, I could instead manually manage three different C-Arrays -- One for the Date String (2-Dimensional), One for the temperature (1-Dimensional) and One for the Rainfall (1-Dimensional). I could keep track of the current Day by referencing the current index of the iterated C-Arrays.

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  • How are developers using source control, I am trying to find the most efficient way to do source con

    - by RJ
    I work in a group of 4 .Net developers. We rarely work on the same project at the same time but it does happen from time to time.We use TFS for source control. My most recent example is a project I just placed into production last night that included 2 WCF services and a web application front end. I worked out of a branch called "prod" because the application is brand new and has never seen the light of day. Now that the project is live, I need to branch off the prod branch for features, bugs, etc... So what is the best way to do this? Do I simple create a new branch and sort of archive the old branch and never use it again? Do I branch off and then merge my branch changes back into the prod branch when I want to deploy to production? And what about the file and assembly version. They are currently at 1.0.0.0. When do they change and why? If I fix a small bug, which number changes if any? If I add a feature, which number changes if any? What I am looking for is what you have found to be the best way to efficiently manage source control. Most places I have worked always seem to bang heads with the source control system in on way or another and I would just like to find out what you have found that works the best.

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  • Is there a more efficient way to do this?

    - by garethdn
    I'm hoping there is a better way to the following. I'm creating a jigsaw-type application and this is the current code i'm using: -(void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; //location of current touch CGPoint location = [touch locationInView:self.view]; if ([touch view] == img1) { [self animateFirstTouch:img1 withLocation:location]; } else if ([touch view] == img2) { [self animateFirstTouch:img2 withLocation:location]; } else if ([touch view] == img3) { [self animateFirstTouch:img3 withLocation:location]; } else if ([touch view] == img4) { [self animateFirstTouch:img4 withLocation:location]; } else if { ...... ...... } else if ([touch view] == img40) { [self animateFirstTouch:img40 withLocation:location]; return; } } I'm hoping that there is a better, more efficieny way to do this, rather than naming every image. I'm thinking something like, if touch view is equal to a UIImageView, then perform some task. The same for touchesEnded: -(void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; //location of current touch CGPoint location = [touch locationInView:self.view]; if ([touch view] == image1) { [self animateReleaseTouch:image1 withLocation:location]; } else if ([touch view] == image2) { [self animateReleaseTouch:image2 withLocation:location]; } else if ([touch view] == image3) { [self animateReleaseTouch:image3 withLocation:location]; } else if ([touch view] == image4) { [self animateReleaseTouch:image4 withLocation:location]; } else if{ ...... ...... } else if ([touch view] == image40) { [self animateReleaseTouch:image40 withLocation:location]; } return; } Any help please?

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  • How can I make the storage of C++ lambda objects more efficient?

    - by Peter Ruderman
    I've been thinking about storing C++ lambda's lately. The standard advice you see on the Internet is to store the lambda in a std::function object. However, none of this advice ever considers the storage implications. It occurred to me that there must be some seriously black voodoo going on behind the scenes to make this work. Consider the following class that stores an integer value: class Simple { public: Simple( int value ) { puts( "Constructing simple!" ); this->value = value; } Simple( const Simple& rhs ) { puts( "Copying simple!" ); this->value = rhs.value; } Simple( Simple&& rhs ) { puts( "Moving simple!" ); this->value = rhs.value; } ~Simple() { puts( "Destroying simple!" ); } int Get() const { return this->value; } private: int value; }; Now, consider this simple program: int main() { Simple test( 5 ); std::function<int ()> f = [test] () { return test.Get(); }; printf( "%d\n", f() ); } This is the output I would hope to see from this program: Constructing simple! Copying simple! Moving simple! Destroying simple! 5 Destroying simple! Destroying simple! First, we create the value test. We create a local copy on the stack for the temporary lambda object. We then move the temporary lambda object into memory allocated by std::function. We destroy the temporary lambda. We print our output. We destroy the std::function. And finally, we destroy the test object. Needless to say, this is not what I see. When I compile this on Visual C++ 2010 (release or debug mode), I get this output: Constructing simple! Copying simple! Copying simple! Copying simple! Copying simple! Destroying simple! Destroying simple! Destroying simple! 5 Destroying simple! Destroying simple! Holy crap that's inefficient! Not only did the compiler fail to use my move constructor, but it generated and destroyed two apparently superfluous copies of the lambda during the assignment. So, here finally are the questions: (1) Is all this copying really necessary? (2) Is there some way to coerce the compiler into generating better code? Thanks for reading!

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  • Python 3: Most efficient way to create a [func(i) for i in range(N)] list comprehension

    - by mejiwa
    Say I have a function func(i) that creates an object for an integer i, and N is some nonnegative integer. Then what's the fastest way to create a list (not a range) equal to this list mylist = [func(i) for i in range(N)] without resorting to advanced methods like creating a function in C? My main concern with the above list comprehension is that I'm not sure if python knows beforehand the length of range(N) to preallocate mylist, and therefore has to incrementally reallocate the list. Is that the case or is python clever enough to allocate mylist to length N first and then compute it's elements? If not, what's the best way to create mylist? Maybe this? mylist = [None]*N for i in range(N): mylist[i] = func(i)

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  • Is there an efficient way to write this PHP if / else statement?

    - by nvoyageur
    I've written a simple issue tracker for my web app. I have some comments that I want to keep private (only a role of 'root' can see them). Is there a better way to write the following so I do not need the empty else section? $role will be 'root' or some other values $is_private will be true if the comment is private <?php // Don't show private comments to non-root users if ($is_private && 'root' != $role): // NON Root cannot see private else: ?> <div class="comment <?= $is_private ? 'private' : '' ; ?>"> <div class="comment-meta toolbar"> <?= $is_private ? 'PRIVATE - ': ''; ?> <span class="datestamp"><?= $created_at; ?></span> - <span class="fullname"><?= $fname . ' ' . $lname; ?></span></div> <p class="content"><?= nl2br($body); ?></p> </div> <?php endif; ?>

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  • What is the most efficient way of associating information with a Type in .Net?

    - by Miguel Angelo
    I want to associate custom data to a Type, and retrieve that data in run-time, blasingly fast. This is just my imagination, of my perfect world: var myInfo = typeof(MyClass).GetMyInformation(); this would be very fast... of course this does not exist! If it did I would not be asking. hehe ;) This is the way using custom attributes: var myInfo = typeof(MyClass).GetCustomAttribute("MyInformation"); this is slow because it requires a lookup of the string "MyInformation" This is a way using a Dictionary<Type, MyInformation: var myInfo = myInformationDictionary[typeof(MyClass)]; This is also slow because it is still a lookup of 'typeof(MyClass)'. I know that dictionary is very fast, but this is not enough... it is not as fast as calling a method. It is not even the same order of speed. I am not saying I want it to be as fast as a method call. I want to associate information with a type and access it as fast as possible. I am asking whether there is a better way, or event a best way of doing it. Any ideas?? Thanks!

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  • Is MS Access still the most efficient RAD tool for small-scale custom apps?

    - by FastAl
    Of the many other development tools I've used, nothing holds a candle to the 'Functionality to Development Effort' ratio of MS Access. The reason I am asking is that I have been out of the language selection process for a few years, working on a large .Net system, and am only anecdotally familiar with the latest development tools outside the .Net world. I'm well aware of the limitations of Access, but for a limited concurrency (usually only 1 user at a time), small business, custom app, has anybody found a comparable end-to-end solution or combination that comes close? It doesn't have to be free, open source, or even Windows based. It just has to allow the same speed of development and maintenance, and maybe even provide some additional amenities like seamless autointegration with a server-based DB Engine (like Access does with its own 'Jet' dbms), better web support, and a file format more compatible with source control. I don't want to miss out on anything. Please share your development experience with your suggestions. Thanks.

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  • SQL: Is there a more efficient way to calculate elapsed hours, minutes, seconds?

    - by hamlin11
    I'm using Computed Columns to provide me with the following information: Hours, Minutes, and Seconds between a Start DateTime and Finish DateTime (Where Minutes and Seconds are between 0 and 59 and Hours can be any value 0 or greater) Computed Column for Seconds: datediff(second,[Start],[Finish]) % 60 Computed Column for Minutes: floor(datediff(second,[Start],[Finish]) / 60.0) % 60 Computed Column for Hours: floor(datediff(second,[Start],[Finish]) / 3600.0) Here's the table for reference Note: I'm also calculating TotalElapsedSeconds, TotalElapsedMinutes, and TotalElapsedHours in other computed columns, but those are easy. I just feel like I might be missing out on a nice built in function in SQL.

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  • What C# container is most resource-efficient for existence for only one operation?

    - by ccornet
    I find myself often with a situation where I need to perform an operation on a set of properties. The operation can be anything from checking if a particular property matches anything in the set to a single iteration of actions. Sometimes the set is dynamically generated when the function is called, some built with a simple LINQ statement, other times it is a hard-coded set that will always remain the same. But one constant always exists: the set only exists for one single operation and has no use before or after it. My problem is, I have so many points in my application where this is necessary, but I appear to be very, very inconsistent in how I store these sets. Some of them are arrays, some are lists, and just now I've found a couple linked lists. Now, none of the operations I'm specifically concerned about have to care about indices, container size, order, or any other functionality that is bestowed by any of the individual container types. I picked resource efficiency because it's a better idea than flipping coins. I figured, since array size is configured and it's a very elementary container, that might be my best choice, but I figure it is a better idea to ask around. Alternatively, if there's a better choice not out of resource-efficiency but strictly as being a better choice for this kind of situation, that would be nice as well.

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  • Efficient and accurate way to compact and compare Python lists?

    - by daveslab
    Hi folks, I'm trying to a somewhat sophisticated diff between individual rows in two CSV files. I need to ensure that a row from one file does not appear in the other file, but I am given no guarantee of the order of the rows in either file. As a starting point, I've been trying to compare the hashes of the string representations of the rows (i.e. Python lists). For example: import csv hashes = [] for row in csv.reader(open('old.csv','rb')): hashes.append( hash(str(row)) ) for row in csv.reader(open('new.csv','rb')): if hash(str(row)) not in hashes: print 'Not found' But this is failing miserably. I am constrained by artificially imposed memory limits that I cannot change, and thusly I went with the hashes instead of storing and comparing the lists directly. Some of the files I am comparing can be hundreds of megabytes in size. Any ideas for a way to accurately compress Python lists so that they can be compared in terms of simple equality to other lists? I.e. a hashing system that actually works? Bonus points: why didn't the above method work?

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  • Is a clear and replace more efficient than a loop checking all records?

    - by Matt
    I have a C# List, that is filled from a database.. So far its only 1400 records, but I expect it to grow a LOT.. Routinely I do a check for new data on the entire list.. What I'm trying to figure out is this, is it faster to simply clear the List and reload all the data from the table, or would checking each record be faster.. Intuition tells me that the dump and load method would be faster, but I thought I should check first...

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