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• How to partition a plane

  - by puls200

  Let's say I have a fixed number (X) of points, e.g. coordinates within a given plane (I think you can call it a 2-D point cloud). These points should be partitioned into Y polygons where Y < X. The polygons should not overlap. It would be wonderful if the polygons were konvex (like a Voronoi diagram). Imagine it like locations forming countries. For example, I have 12 points and want to create 3 polygons with 4 points each. I thought about creating a grid which covers the points. Then iterate across the points, assigning them to the closest grid cells. Maybe I miss the obvious? I am sure there are better solutions. Thanks, Daniel I just found an optimization (kmeans++) .Maybe this will yield better results..

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• Is it inefficient to access a python class member container in a loop statement?

  - by Dave

  Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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• Using *.html extension in dynamic URL's for SEO

  - by lostaman

  Hi all My situation is. I have a project planned to be built on ASP.NET MVC 2. And one of the major requirements is SEO optimization. A customer wants to use static-like URLs that end up with .html extension for this project that make URLs more SEO friendly. E.g. "mysite.com/about.html " or "mysite.com/items/getitem/5.html" etc. I wonder is there any benefit from SEO perspective to use .html extension in dynamic URLs? Are Google and other search engines rank work better with such URLs?

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• Custom sort logic in OrderBy using LINQ

  - by Bala R

  What would be the right way to sort a list of strings where I want items starting with an underscore '_', to be at the bottom of the list, otherwise everything is alphabetical. Right now I'm doing something like this, autoList.OrderBy(a => a.StartsWith("_") ? "ZZZZZZ"+a : a ) EDIT: I ended up using something like this; optimization suggestions welcome! private class AutoCompleteComparer : IComparer<String> { public int Compare(string x, string y) { if (x.StartsWith("_") && y.StartsWith("_") || (!x.StartsWith("_") && !y.StartsWith("_"))) { return x.CompareTo(y); } else if (x.StartsWith("_")) { return 1; } else if (y.StartsWith("_")) { return -1; } return 0; } }

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• Can Graphical Operations be combined in Qt or any other library ?

  - by Sunny

  Hi, Here is a Scenario, A series of operations that I will call for painting, QPainter p(this); 1). p.fillRect(0,0,320,240, RED_COLOR) 2) p.drawLine(0,0,100,100, BLUE_COLOR) 3) p.fillRect(0,0,320,240, YELLOW_COLOR) Now I want that painter should not draw first FillRect Function. It should not draw line. It should only perform last operation. Is there any way to achive this optimization in Qt. Is this type of drawing/painting optimizations are supported by any library?

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• Why do debug symbols so adversely affect the performance of threaded applications on Linux?

  - by fluffels

  Hi. I'm writing a ray tracer. Recently, I added threading to the program to exploit the additional cores on my i5 Quad Core. In a weird turn of events the debug version of the application is now running slower, but the optimized build is running faster than before I added threading. I'm passing the "-g -pg" flags to gcc for the debug build and the "-O3" flag for the optimized build. Host system: Ubuntu Linux 10.4 AMD64. I know that debug symbols add significant overhead to the program, but the relative performance has always been maintained. I.e. a faster algorithm will always run faster in both debug and optimization builds. Any idea why I'm seeing this behavior?

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• Create an seo and web accessibility analyzer

  - by rebellion

  I'm thinking of making a little web tool for analyzing the search engine optimization and web accessiblity of a whole website. First of all, this is just a private tool for now. Crawling a whole website takes up alot of resources and time. I've found out that wget is the best option for downloading the markup for a whole site. I plan on using PHP/MySQL (maybe even CodeIgniter), but I'm not quite sure if that's the right way to do it. There's always someone who recommends Python, Ruby or Perl. I only know PHP and a little bit Rails. I've also found a great HTML DOM parser class in PHP on SourceForge. But, the thing is, I need some feedback on what I should and should not do. Everything from how I should make the crawl process to what I should be checking for in regards to SEO and WCAG. So, what comes to your mind when you hear this?

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• What is the time taken by java to call a method in another package?

  - by satish

  I have an assignment where i need to do feasibility study on two of my approaches and find optimized one. There are two packages A and B User input is gathered in A and then sent to B for execution. Now my approaches are 1. Call B methods from package A one by one. 2. Create a common method in B and send all the input as parameters. Which is feasible and best one, I know 2 is good in terms of code optimization and less number of calls. But, I want to understand what will be the execution time difference in above approaches How much time does java take to call method in another package? Is there any default value like x nano seconds or y milli seconds. Based on the time taken I can choose the appropiate one. Thanks

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• Non-Latin characters in URLs - is it better to encode them or replace with their Latin "counterparts

  - by Pawel Krakowiak

  We're implementing a blog for a site which supports six different languages and five of them have non-Latin characters in their alphabets. We are not sure whether we should have them encoded (that is what we're doing at the moment) Létání s potravinami: Co je dovoleno? becomes l%c3%a9t%c3%a1n%c3%ad-s-potravinami-co-je-dovoleno and the browser displays it as létání-s-potravinami-co-je-dovoleno. or if we should replace them with their Latin "counterparts" (similar looking letters) Létání s potravinami: Co je dovoleno? becomes letani-s-potravinami-co-je-dovoleno. I can't find a definitive answer as to what's better from SEO perspective? Search engine optimization is very important for us. Which approach would you suggest?

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• Any way to avoid a filesort when order by is different to where clause?

  - by Julian

  I have an incredibly simple query (table type InnoDb) and EXPLAIN says that MySQL must do an extra pass to find out how to retrieve the rows in sorted order. SELECT * FROM `comments` WHERE (commentable_id = 1976) ORDER BY created_at desc LIMIT 0, 5 exact explain output: table select_type type extra possible_keys key key length ref rows comments simple ref using where; using filesort common_lookups common_lookups 5 const 89 commentable_id is indexed. Comments has nothing trick in it, just a content field. The manual suggests that if the order by is different to the where, there is no way filesort can be avoided. http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html I also tried order by id as well as it's equivalent but makes no difference, even if I add id as an index (which I understand is not required as id is indexed implicitly in MySQL). thanks in advance for any ideas!

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• How to Optimize Combined Graphical Operations?

  - by Sunny

  Hi, Here is a Scenario, A series of operations that I will call for painting, QPainter p(this); 1). p.fillRect(0,0,320,240, RED_COLOR) 2) p.drawLine(0,0,100,100, BLUE_COLOR) 3) p.fillRect(0,0,320,240, YELLOW_COLOR) Now I want that painter should not draw first FillRect Function. It should not draw line. It should only perform last operation. Is there any way to achive this optimization in Qt. Is this type of drawing/painting optimizations are supported by any library?

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• how to optimize sql server table for faster response?

  - by Thomas

  i found a in a table there are 50 thousands records and it takes one minute when we fetch data from sql server table just by issuing a sql. there are one primary key that means a already a cluster index is there. i just do not understand why it takes one minute. beside index what are the ways out there to optimize a table to get the data faster. in this situation what i need to do for faster response. also tell me how we can write always a optimize sql. please tell me all the steps in detail for optimization. thanks.

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• JSF Pages call ManagedBeans that are not defined on the page and call all getters sometimes more tha

  - by Bill Leeper

  I have several JSF pages that are initializing and accessing ManagedBeans that are not even used on that page. This is creating a really hairy problem for initialization. I either have to make them all session scope and continually make calls to re-inialize or take the performance hit of having them read large amounts of data from the DB whenever they decide to initialize. Some of the managed beans being accessed are not even defined on the page in question. I have done some optimization based on comments related to multiple calls to getters, but I still have the issue that I have a very specialized (and expensive to initialize) bean that is getting called when I don't want it initialized. Any insight into why/what JSF calls might do something like this. I have a very complex page making use of JSTL, Tomahawk and standard JSF tags. I could include code, but its very complex and sensitive in nature.

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• Is "}while(0);" always equal to "break;}while(1);" ?

  - by Hernán Eche

  I have compared gcc assembler output of do{ //some code }while(0); with do{ //some code break; }while(1); The output is equal, with or without optimization but.. It's always that way? No experiment can prove theories, they can only show they are wrong And because (I hope) programming is not an experimental science, and results can be predicted (at least simple things) I want to be sure next time I reeplace a break;}while(1); for the clearer (and less risky) while(0); Thank you for reading

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• ASP NET forms Authorization: how to reduce duration?

  - by eddo

  I've got a web page which is implementing cookie based ASPNET Forms Authentication. Once the user has logged in the page, he can edit some information using a form which is created using a partialview and returned to him as a dialog for editing. The action linked to the partial view is decorated as follows: [HttpGet] [OutputCache(Duration = 0, VaryByParam = "None")] [Authorize(Roles = "test")] public ActionResult changeTripInfo(int tripID, bool ovride=false) { ... } The problem i am experiencing is the latency between the request and the time when the dialog is shown to the user: time ranges between 800 and 1100 ms which is not justified by the complexity of the form. Investigating with Glimpse turns out that the time to process the AuthorizeAttribute (see snip) sums up to at least 650 ms which is troubling me. Looking at the Sql server log, the call which checks the user roles takes, as expected, virtually nothing (duration 0). How can I reduce this time? Am I missing some optimization?

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• Is there a way to launch an aggressive and complete garbage collection in Java?

  - by Gnoupi

  For memory optimization reasons, I'm launching myself the garbage collector during profiling, to check if objects are correctly cleaned after disposing of them. The call to garbage collector is not enough, though, and it seems that there is no guarantee of what it will clean. Is there a way to call it, to be sure it will recover as much as it can, in profiling conditions (this would have no point in production, of course)? Or is "calling it several times" the only way to be "almost sure"? Or did I simply misunderstand something about the Garbage Collector?

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• Can I replicate some of the optimisations done by the JVM by hand?

  - by Subb

  I'm working on a Sudoku solver at school and we're having a little performance contest. Right now, my algorithm is pretty fast on the first run (about 2.5ms), but even faster when I solve the same puzzle 10 000 times (about 0.5ms for each run). Those timing are, of course, depend of the puzzle being solved. I know the JVM do some optimization when a method is called multiple time, and this is what I suspect is happening. I don't think I can further optimize the algorithm itself (though I'll keep looking), so I was wondering if I could replicate some of the optimizations done by the JVM. Note : compiling to native code is not an option Thanks!

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• Is there a way to ignore Cache errors in Django?

  - by Josh Smeaton

  I've just set our development Django site to use redis for a cache backend and it was all working fine. I brought down redis to see what would happen, and sure enough Django 404's due to cache backend behaviour. Either the Connection was refused, or various other errors. Is there any way to instruct Django to ignore Cache errors, and continue processing the normal way? It seems weird that caching is a performance optimization, but can bring down an entire site if it fails. I tried to write a wrapper around the backend like so: class CacheClass(redis_backend.CacheClass): """ Wraps the desired Cache, and falls back to global_settings default on init failure """ def __init__(self, server, params): try: super(CacheClass, self).__init__(server, params) except Exception: from django.core import cache as _ _.cache = _.get_cache('locmem://') But that won't work, since I'm trying to set the cache type in the call that sets the cache type. It's all a very big mess. So, is there any easy way to swallow cache errors? Or to set the default cache backend on failure?

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• Python design mistakes

  - by Andrea

  A while ago, when I was learning Javascript, I studied Javascript: the good parts, and I particularly enjoyed the chapters on the bad and the ugly parts. Of course, I did not agree with everything, as summing up the design defects of a programming language is to a certain extent subjective - although, for instance, I guess everyone would agree that the keyword with was a mistake in Javascript. Nevertheless, I find it useful to read such reviews: even if one does not agree, there is a lot to learn. Is there a blog entry or some book describing design mistakes for Python? For instance I guess some people would count the lack of tail call optimization a mistake; there may be other issues (or non-issues) which are worth learning about.

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• Converting keys of an array/object-tree to lowercase

  - by tstenner

  Im currently optimizing a PHP application and found one function being called around 10-20k times, so I'd thought I'd start optimization there. function keysToLower($obj) { if(!is_object($obj) && !is_array($obj)) return $obj; foreach($obj as $key=>$element) { $element=keysToLower($element); if(is_object($obj)) { $obj->{strtolower($key)}=$element; if(!ctype_lower($key)) unset($obj->{$key}); } else if(is_array($obj) && ctype_upper($key)) { $obj[strtolower($key)]=$element; unset($obj[$key]); } } return $obj; } Most of the time is spent in recursive calls (which are quite slow in PHP), but I don't see any way to convert it to a loop. What would you do?

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• Need help in sorting the programming buzz-words

  - by cwap

  How do you sort out the good buzz from the bad buzz? - I really need your help here :) I see a lot of buzz-words nowadays, both here on SO and in school. For example, we had a teacher who everyone respected, who said "be careful about gold-plating and death-by-interfacing". Now, everyone and their mama cries whenever I'm creating an interface.. Another example would be here on SO where lately "premature optimization is the root of all evil", so everytime someone asks a perfomance question, he'll get that sentence thrown in his face. A few months ago I remember it was all about NHibernate in here, etc., etc... These things comes and goes, but only the good buzz stays. Now, how do you seperate the good from the bad? By reading blogs from respected persons? By trying to come to a conclusion on your own, and then try to convince others that you're right? By simply ignoring it?

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• What's this UI pattern called?

  - by Bears will eat you

  I'm trying to figure out what this sort of thing is called, and eventually how I can create one in a web browser. It looks like this (screenshot of the first app that came to mind): The specific component/pattern I'm looking for is the two list boxes ("Included Gear" and "Excluded Gear") that represent inclusion/exclusion of items from a set. I'm not really looking for the WPF name (if there is one) but it might be helpful. I am looking for the name of this thingy, if there is one, and if you really want to make my day, you can point me toward a jQuery or YUI way of making one of these dealies in a browser. In case you were wondering, the screenshot is a World of Warcraft gear optimization program. Go figure why it was the first program that came to mind when I was trying to think of an example.

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• Access static constant variable from multiple threads in C

  - by user325519

  I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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• Select rows where column LIKE dictionary word

  - by Gerve

  I have 2 tables: Dictionary - Contains roughly 36,000 words CREATE TABLE IF NOT EXISTS `dictionary` ( `word` varchar(255) NOT NULL, PRIMARY KEY (`word`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1; Datas - Contains roughly 100,000 rows CREATE TABLE IF NOT EXISTS `datas` ( `ID` int(11) NOT NULL AUTO_INCREMENT, `hash` varchar(32) NOT NULL, `data` varchar(255) NOT NULL, `length` int(11) NOT NULL, `time` int(11) NOT NULL, PRIMARY KEY (`ID`), UNIQUE KEY `hash` (`hash`), KEY `data` (`data`), KEY `length` (`length`), KEY `time` (`time`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=105316 ; I would like to somehow select all the rows from datas where the column data contains 1 or more words. I understand this is a big ask, it would need to match all of these rows together in every combination possible, so it needs the best optimization. I have tried the below query, but it just hangs for ages: SELECT `datas`.*, `dictionary`.`word` FROM `datas`, `dictionary` WHERE `datas`.`data` LIKE CONCAT('%', `dictionary`.`word`, '%') AND LENGTH(`dictionary`.`word`) > 3 ORDER BY `length` ASC LIMIT 15 I have also tried something similar to the above with a left join, and on clause that specified the like statement.

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• Fastest way to check for value existance.

  - by Itay Moav

  I have a list of values I have to check my input against it for existence. What is the faster way? This is really out of curiosity on how the internals work, not any stuff about premature optimization etc... 1. $x=array('v'=>'','c'=>'','w'=>); .. .. array_key_exists($input,$x); 2. $x=array('v','c','w'); .. .. in_array($input,$x);

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