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  • Are there advantages for using recursion over iteration - other than sometimes readability and elegance?

    - by Prog
    I am about to make two assumptions. Please correct me if they're wrong: There isn't a recursive algorithm without an iterative equivalent. Iteration is always cheaper performance-wise than recursion (at least in general purpose languages such as Java, C++, Python etc.). If it's true that recursion is always more costly than iteration, and that it can always be replaced with an iterative algorithm (in languages that allow it) - than I think that the two remaining reasons to use recursion are: elegance and readability. Some algorithms are expressed more elegantly with recursion. E.g. scanning a binary tree. However apart from that, are there any reasons to use recursion over iteration? Does recursion have advantages over iteration other than sometimes elegance and readability?

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  • Disco/MapReduce: Using results of previous iteration as input to new iteration

    - by muckabout
    Currently am implementing PageRank on Disco. As an iterative algorithm, the results of one iteration are used as input to the next iteration. I have a large file which represents all the links, with each row representing a page and the values in the row representing the pages to which it links. For Disco, I break this file into N chunks, then run MapReduce for one round. As a result, I get a set of (page, rank) tuples. I'd like to feed this rank to the next iteration. However, now my mapper needs two inputs: the graph file, and the pageranks. I would like to "zip" together the graph file and the page ranks, such that each line represents a page, it's rank, and it's out links. Since this graph file is separated into N chunks, I need to split the pagerank vector into N parallel chunks, and zip the regions of the pagerank vectors to the graph chunks This all seems more complicated than necessary, and as a pretty straightforward operation (with the quintessential mapreduce algorithm), it seems I'm missing something about Disco that could really simplify the approach. Any thoughts?

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  • Iterative and Incremental Principle Series 4: Iteration Planning – (a.k.a What should I do today?)

    - by llowitz
    Welcome back to the fourth of a five part series on applying the Iteration and Incremental principle.  During the last segment, we discussed how the Implementation Plan includes the number of the iterations for a project, but not the specifics about what will occur during each iteration.  Today, we will explore Iteration Planning and discuss how and when to plan your iterations. As mentioned yesterday, OUM prescribes initially planning your project approach at a high level by creating an Implementation Plan.  As the project moves through the lifecycle, the plan is progressively refined.  Specifically, the details of each iteration is planned prior to the iteration start. The Iteration Plan starts by identifying the iteration goal.  An example of an iteration goal during the OUM Elaboration Phase may be to complete the RD.140.2 Create Requirements Specification for a specific set of requirements.  Another project may determine that their iteration goal is to focus on a smaller set of requirements, but to complete both the RD.140.2 Create Requirements Specification and the AN.100.1 Prepare Analysis Specification.  In an OUM project, the Iteration Plan needs to identify both the iteration goal – how far along the implementation lifecycle you plan to be, and the scope of work for the iteration.  Since each iteration typically ranges from 2 weeks to 6 weeks, it is important to identify a scope of work that is achievable, yet challenging, given the iteration goal and timeframe.  OUM provides specific guidelines and techniques to help prioritize the scope of work based on criteria such as risk, complexity, customer priority and dependency.  In OUM, this prioritization helps focus early iterations on the high risk, architecturally significant items helping to mitigate overall project risk.  Central to the prioritization is the MoSCoW (Must Have, Should Have, Could Have, and Won’t Have) list.   The result of the MoSCoW prioritization is an Iteration Group.  This is a scope of work to be worked on as a group during one or more iterations.  As I mentioned during yesterday’s blog, it is pointless to plan my daily exercise in advance since several factors, including the weather, influence what exercise I perform each day.  Therefore, every morning I perform Iteration Planning.   My “Iteration Plan” includes the type of exercise for the day (run, bike, elliptical), whether I will exercise outside or at the gym, and how many interval sets I plan to complete.    I use several factors to prioritize the type of exercise that I perform each day.  Since running outside is my highest priority, I try to complete it early in the week to minimize the risk of not meeting my overall goal of doing it twice each week.  Regardless of the specific exercise I select, I follow the guidelines in my Implementation Plan by applying the 6-minute interval sets.  Just as in OUM, the iteration goal should be in context of the overall Implementation Plan, and the iteration goal should move the project closer to achieving the phase milestone goals. Having an Implementation Plan details the strategy of what I plan to do and keeps me on track, while the Iteration Plan affords me the flexibility to juggle what I do each day based on external influences thus maximizing my overall success. Tomorrow I’ll conclude the series on applying the Iterative and Incremental approach by discussing how to manage the iteration duration and highlighting some benefits of applying this principle.

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  • Invert a string: Recursion vs iteration in javascript

    - by steweb
    Hi all, one month ago I've been interviewed by some google PTO members. One of the questions was: Invert a string recursively in js and explain the running time by big O notation this was my solution: function invert(s){ return (s.length > 1) ? s.charAt(s.length-1)+invert(s.substring(0,s.length-1)) : s; } Pretty simple, I think. And, about the big-o notation, I quickly answered O(n) as the running time depends linearly on the input. - Silence - and then, he asked me, what are the differences in terms of running time if you implement it by iteration? I replied that sometimes the compiler "translate" the recursion into iteration (some programming language course memories) so there are no differences about iteration and recursion in this case. Btw since I had no feedback about this particular question, and the interviewer didn't answer "ok" or "nope", I'd like to know if you maybe agree with me or if you can explain me whether there could be differences about the 2 kind of implementations. Thanks a lot and Regards!

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  • Recursion and Iteration

    - by Doug
    What is the difference? Are these the same? If not, can someone please give me an example? MW: Iteration - 1 : the action or a process of iterating or repeating: as a : a procedure in which repetition of a sequence of operations yields results successively closer to a desired result b : the repetition of a sequence of computer instructions a specified number of times or until a condition is met Recusion - 3 : a computer programming technique involving the use of a procedure, subroutine, function, or algorithm that calls itself one or more times until a specified condition is met at which time the rest of each repetition is processed from the last one called to the first

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  • array iteration strstr in c

    - by lex0273
    I was wondering if it's safe to do the following iteration to find the first occurrence of str within the array or if there is a better way. Thanks #include <stdio.h> #include <string.h> const char * list[] = {"One","Two","Three","Four","Five"}; char *c(char * str) { int i; for (i = 0; i < 5; i++) { if (strstr(str, list[i]) != NULL) return list[i]; } return "Not Found"; } int main() { char str[] = "This is a simple string of hshhs wo a char"; printf("%s", c(str)); return 0; }

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  • iteration in latex

    - by Tim
    Hi, I would like to use some iteration control flow to simplify the following latex code \begin{sidewaystable} \caption{A glance of images} \centering \begin{tabular}{| c ||c| c| c |c| c|| c |c| c|c|c| } \hline \backslashbox{Theme}{Class} &\multicolumn{5}{|c|}{Class 0} & \multicolumn{5}{|c|}{Class 1} \\ \hline \hline 1 & \includegraphics[scale=2]{../../results/1/0_1.eps} &\includegraphics[scale=2]{../../results/1/0_2.eps} &\includegraphics[scale=2]{../../results/1/0_3.eps} &\includegraphics[scale=2]{../../results/1/0_4.eps} &\includegraphics[scale=2]{../../results/1/0_5.eps} &\includegraphics[scale=2]{../../results/1/1_1.eps} &\includegraphics[scale=2]{../../results/1/1_2.eps} &\includegraphics[scale=2]{../../results/1/1_3.eps} &\includegraphics[scale=2]{../../results/1/1_4.eps} &\includegraphics[scale=2]{../../results/1/1_5.eps} \\ \hline \hline 2 & \includegraphics[scale=2]{../../results/2/0_1.eps} &\includegraphics[scale=2]{../../results/2/0_2.eps} &\includegraphics[scale=2]{../../results/2/0_3.eps} &\includegraphics[scale=2]{../../results/2/0_4.eps} &\includegraphics[scale=2]{../../results/2/0_5.eps} &\includegraphics[scale=2]{../../results/2/1_1.eps} &\includegraphics[scale=2]{../../results/2/1_2.eps} &\includegraphics[scale=2]{../../results/2/1_3.eps} &\includegraphics[scale=2]{../../results/2/1_4.eps} &\includegraphics[scale=2]{../../results/2/1_5.eps} \\ \hline ... % similarly for 3, 4, ..., 22 \hline 23 & \includegraphics[scale=2]{../../results/23/0_1.eps} &\includegraphics[scale=2]{../../results/23/0_2.eps} &\includegraphics[scale=2]{../../results/23/0_3.eps} &\includegraphics[scale=2]{../../results/23/0_4.eps} &\includegraphics[scale=2]{../../results/23/0_5.eps} &\includegraphics[scale=2]{../../results/23/1_1.eps} &\includegraphics[scale=2]{../../results/23/1_2.eps} &\includegraphics[scale=2]{../../results/23/1_3.eps} &\includegraphics[scale=2]{../../results/23/1_4.eps} &\includegraphics[scale=2]{../../results/23/1_5.eps} \\ \hline \end{tabular} \end{sidewaystable} I learn that the forloop package provides the for loop. But I am not sure how to apply it to my case? Or other methods not by forloop? Thanks and regards! Update: If I also want to simply another similar case, where the only difference is that the directory does not run from 1, 2, to 23, but in some arbitrary order such as 3, 2, 6, 9,..., or even a list of strings such as dira, dirc, dird, dirb,.... How to make the latex code into loops then? Thanks!

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  • simplexml object node iteration

    - by MorbidWrath
    I have an xml file that I'm parsing with php's simplexml, but I'm having an issue with an iteration through nodes. the xml: <channel> <item> <title>Title1</title> <category>Cat1</category> </item> <item> <title>Title2</title> <category>Cat1</category> </item> <item> <title>Title3</title> <category>Cat2</category> </item> </channel> my counting function: public function cat_count($cat){ $count = 0; $items = $this->xml->channel->item; $size = count($size); for($i=0;$i<$size;$i++){ if($items[$i]->category == $cat){ $count++; } } return $count; } Am I overlooking an error in my code, or is there another preferred method for iterating through the nodes? I've also used a foreach and while statement with no luck, so I'm at a loss. Any suggestions?

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  • Calculations on the iteration count in for loop in Ruby 1.8.7

    - by user1805035
    I was playing around with Ruby and Latex to create a color coding set. I'm more than a novice with C++, but haven't looked at Ruby until now. So, still learning a lot of coding. I have the following block of code below. When attempting to run this, band1 = 1e+02. I've tried band1 = (BigDecimal(i) * 100).to_f thinking maybe there was some odd floating point issue. This is just me trying anything though as an integer multiplied by an integer should create an integer, if I'm still thinking correctly. I've tried a variety of other things as well (things that I can do in C++, but this ain't C++), but to no avail. (1..9).each do |i| #Band 1 (0..9).each do |j| #Band 2 (0..11).each do |k| #Band 3 #Band 3 Start #these are the colors of the resistor bands b1 = $c_band12[i] b2 = $c_band12[j] b3 = $c_band3[k] b4 = "Gold" oms = ((i*100) + (j*10)) * $mult[k] band1 = i*100 band2 = j band3 = $mult[k] end end end Not sure what I'm missing. Should I be using .each_with_index through these iterations? I've tried this: (1..9).each_with_index {|i, indexi| #Band 1 (0..9).each_with_index {|j, indexj| #Band 2 (0..11).each_with_index {|k, indexk| #Band 3 #Band 3 Start #these are the colors of the resistor bands b1 = $c_band12[i] b2 = $c_band12[j] b3 = $c_band3[k] b4 = "Gold" oms = ((i*100) + (j*10)) * $mult[k] band1 = indexk * 100 and I get the same answer. I can't see why 1*100 should equate to such a large number? Thank you, AT

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  • Finishing an iteration early

    - by f1dave
    I'd like some input on this on those working with agile methodologies... A current project is finding that development on our planned user stories is finishing some time before the end of the iteration, and that the testing effort and business acceptance is what's actually dragging us out longer towards the end. This means that the devs in question have spare time, and they're essentially going out to the iteration+1 backlog and starting work on cards there before our current iteration cards are 'done'. As iteration manager, I want to put a stop to this - I want a more team-orientated approach where the group takes ownership of getting all the cards done, as opposed to "Well, dev's done so what do I dev next?" The problem I face is convincing the team of this. On one hand, I understand why the devs don't want to test the code they've written (there are unit tests they write of course, but the manual testing to be done could be influenced by their bias). The team sees working ahead as making our next iterations easier, because a lot of the work is done before we start. I see this as screwing with the whole system of planning/actuals - but it's difficult to convince the team as to why this matters. What advice can you guys and girls give? How do we stop devs reaching ahead? What should they be doing instead? How much of a problem is this in the scheme of things, if things are still getting done?

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  • Performance: recursion vs. iteration in Javascript

    - by mastazi
    I have read recently some articles (e.g. http://dailyjs.com/2012/09/14/functional-programming/) about the functional aspects of Javascript and the relationship between Scheme and Javascript (the latter was influenced by the first, which is a functional language, while the O-O aspects are inherited from Self which is a prototyping-based language). However my question is more specific: I was wondering if there are metrics about the performance of recursion vs. iteration in Javascript. I know that in some languages (where by design iteration performs better) the difference is minimal because the interpreter / compiler converts recursion into iteration, however I guess that probably this is not the case of Javascript since it is, at least partially, a functional language.

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  • for x in y, type iteration in python. Can I find out what iteration I'm currently on?

    - by foo
    Hi, I have a question about the loop construct in Python in the form of: for x in y: In my case y is a line read from a file and x is separate characters. I would like to put a space after every pair of characters in the output, like this: aa bb cc dd etc. So, I would like to know the current iteration. Is it possible, or do I need to use a more traditional C style for loop with an index?

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  • What is the difference between Sprint and Iteration in SCRUM and length of each Sprint?

    - by kurozakura
    1.Is there a difference between Sprint and an Iteration or one can have Iterations within a Sprint or Sprint is just the terminology used instead of Iteration in SCRUM? It will be helpful if someone can throw some light on this. 2.Suppose there are 4 sprints and you have decided the first sprint will go up to 10days is it required that other 3 sprints should have the same length of the 1st decided sprint's length??.

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  • How to skip to next iteration in jQuery.each() util?

    - by Josh
    I'm trying to iterate through an array of elements. jQuery's documentation says: jquery.Each() documentation Returning non-false is the same as a continue statement in a for loop, it will skip immediately to the next iteration. I've tried calling 'return non-false;' and 'non-false;' (sans return) neither of which skip to the next iteration. Instead, they break the loop. What am i missing?

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  • Gathering all data in single iteration vs using functions for readable code

    - by user828584
    Say I have an array of runners with which I need to find the tallest runner, the fastest runner, and the lightest runner. It seems like the most readable solution would be: runners = getRunners(); tallestRunner = getTallestRunner(runners); fastestRunner = getFastestRunner(runners); lightestRunner = getLightestRunner(runners); ..where each function iterates over the runners and keeps track of the largest height, greatest speed, and lowest weight. Iterating over the array three times, however, doesn't seem like a very good idea. It would instead be better to do: int greatestHeght, greatestSpeed, leastWeight; Runner tallestRunner, fastestRunner, lightestRunner; for(runner in runners){ if(runner.height > greatestHeight) { greatestHeight = runner.height; tallestRunner = runner; } if(runner.speed > ... } While this isn't too unreadable, it can get messy when there is more logic for each piece of information being extracted in the iteration. What's the middle ground here? How can I use only a single iteration while still keeping the code divided into logical units?

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  • How can I use iteration to lead targets?

    - by e100
    In my 2D game, I have stationary AI turrets firing constant speed bullets at moving targets. So far I have used a quadratic solver technique to calculate where the turret should aim in advance of the target, which works well (see Algorithm to shoot at a target in a 3d game, Predicting enemy position in order to have an object lead its target). But it occurs to me that an iterative technique might be more realistic (e.g. it should fire even when there is no exact solution), efficient and tunable - for example one could change the number of iterations to improve accuracy. I thought I could calculate the current range and thus an initial (inaccurate) bullet flight time to target, then work out where the target would actually be by that time, then recalculate a more accurate range, then recalculate flight time, etc etc. I think I am missing something obvious to do with the time term, but my aimpoint calculation does not currently converge after the significant initial correction in the first iteration: import math def aimpoint(iters, target_x, target_y, target_vel_x, target_vel_y, bullet_speed): aimpoint_x = target_x aimpoint_y = target_y range = math.sqrt(aimpoint_x**2 + aimpoint_y**2) time_to_target = range / bullet_speed time_delta = time_to_target n = 0 while n <= iters: print "iteration:", n, "target:", "(", aimpoint_x, aimpoint_y, ")", "time_delta:", time_delta aimpoint_x += target_vel_x * time_delta aimpoint_y += target_vel_y * time_delta range = math.sqrt(aimpoint_x**2 + aimpoint_y**2) new_time_to_target = range / bullet_speed time_delta = new_time_to_target - time_to_target n += 1 aimpoint(iters=5, target_x=0, target_y=100, target_vel_x=1, target_vel_y=0, bullet_speed=100)

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  • Is recursion preferred compare to iteration in multicore era?

    - by prM
    Or say, do multicore CPUs process recursion faster than iteration? Or it simply depends on how one language runs on the machine? like c executes function calls with large cost, comparing to doing simple iterations. I had this question because one day I told one of my friend that recursion isn't any amazing magic that can speed up programs, and he told me that with multicore CPUs recursion can be faster than iteration. EDIT: If we consider the most recursion-loved situation (data structure, function call), is it even possible for recursion to be faster?

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  • Iteration, or copying in XSL, based on a count. How do I do it?

    - by LOlliffe
    I'm trying to create an inventory list (tab-delimited text, for the output) from XML data. The catch is, I need to take the line that I created, and list it multiple times (iterate ???), based on a number found in the XML. So, from the XML below: <?xml version="1.0" encoding="UTF-8"?> <library> <aisle label="AA"> <row>bb</row> <shelf>a</shelf> <books>4</books> </aisle> <aisle label="BB"> <row>cc</row> <shelf>d</shelf> <books>3</books> </aisle> </library> I need to take the value found in "books", and then copy the text line that number of times. The result looking like this: Aisle Row Shelf Titles AA bb a AA bb a AA bb a AA bb a BB cc d BB cc d BB cc d So that the inventory taker, can then write in the titles found on each shelf. I have the basic structure of my XSL, but I'm not sure how to do the "iteration" portion. <?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs" xmlns:xd="http://www.oxygenxml.com/ns/doc/xsl" version="2.0"> <xsl:output omit-xml-declaration="yes"/> <xsl:variable name="tab" select="'&#09;'"/> <xsl:variable name="newline" select="'&#10;'"/> <xsl:template match="/"> <!-- Start Spreadsheet header --> <xsl:text>Aisle</xsl:text> <xsl:value-of select="$tab"/> <xsl:text>Row</xsl:text> <xsl:value-of select="$tab"/> <xsl:text>Shelf</xsl:text> <xsl:value-of select="$tab"/> <xsl:text>Titles</xsl:text> <xsl:value-of select="$newline"/> <!-- End spreadsheet header --> <!-- Start entering values from XML --> <xsl:for-each select="library/aisle"> <xsl:value-of select="@label"/> <xsl:value-of select="$tab"/> <xsl:value-of select="row"/> <xsl:value-of select="$tab"/> <xsl:value-of select="shelf"/> <xsl:value-of select="$tab"/> <xsl:value-of select="$tab"/> <xsl:value-of select="$newline"/> </xsl:for-each> <!-- End of values from XML --> <!-- Iteration of the above needed, based on count value in "books" --> </xsl:template> </xsl:stylesheet> Any help would be greatly appreciated. For starters, is "iteration" the right term to be using for this? Thanks!

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  • My First Iteration Zero

    - by onefloridacoder
    I recently watched a web cast that covered the idea of planning from the concept stage to the product backlog.  It was the first content I had seen related to Iteration Zero and it made a lot of sense from a planning and engagement perspective where the customer is concerned.  It illuminated some of the problems I’ve experienced with getting a large project of the ground.  The idea behind this is to just figure out get everyone to understand what needs to be constructed and to build the initial feature set from a *very* high level.  Once that happens other parts of the high level construction start to take place.  You end up with a feature list that describes what the business wants the system to do, and what it potentially may (or may not) interact with.  Low tech tools are used to create UI mockups that can be used as a starting point for some of the key UI pieces. Toward the end of the webcast they speaker introduced something that was new to me.  He referred to it as an executable skeleton or the steel thread.  The idea with this part of the webcast was to describe walking through the different mocked layers of the application.  Not all layers and collaborators are involved at this stage since it’s Iteration Zero, and each layer is either hard-coded or completely mocked to provide a 35K foot view of how the different layers layers work together.  So imagine two actors on each side of a layer diagram and the flow goes down from the upper left side down through a a consumer, thorough a service layer and then back up the service layer to the destination/actor. I would imagine much could be discussed moving through new/planned or existing/legacy layers, or a little of both to see what’s implied by the current high-level design. One part of the web cast has the business and design team creating the product box (think of your favorite cereal or toy box) with all of the features and even pictures laid out on the outside of the box.  The notion here is that if you handed this box to someone and told them your system was inside they would have an understanding of what the system would be able to do, or the features it could provide.    One of the interesting parts of the webcast was where the speaker described that he worked with a couple of groups in the same room and each group came up with a different product box – the point is that each group had a different idea of what the system was supposed to do.  At this point of the project I thought that to be valuable considering my experience has been that historically this has taken longer than a week to realize that the business unit and design teams see the high level solution differently.  Once my box is finished I plan on moving to the next stage of solution definition which is to plan the UI for this small application using Excel, to map out the UI elements.  I’m my own customer so it feels like cheating, but taking these slow deliberate steps have already provided a few learning opportunities.    So I resist the urge to load all of my user stories into my newly installed VS2010  TFS project and try to reduce or add to, the number of user stories and/or refine the high level estimates I’ve come up with so far.

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  • How to get faster iteration times in android development

    - by Sebastian Bugiu
    I'm creating a game on the android platform that uses the resources/raw folder for assets and scripts. The problem is that every time I change something I have to rebuild the application to test the new variant. Of course this is bad for iteration times. Any ideas about what I can do to avoid rebuilding every time I change something? This *.apk format is getting on my nerves now that I have to recreate it every time I change a word in my scripts. Or at least how to make eclipse auto-rebuild every time I change something in my resources folder so that I don't have to go to Project-Build every time?

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  • Alternatives to javascript function-based iteration (e.g. jQuery.each())

    - by Colin
    I've been watching Google Tech Talks' Speed Up Your Javascript and in talking about loops, the speaker mentions to stay away from function-based iterations such as jQuery.each() (among others, at about 24:05 in the video). He briefly explains why to avoid them which makes sense, but admittedly I don't quite understand what an alternative would be. Say, in the case I want to iterate through a column of table cells and use the value to manipulate the adjacent cell's value (just a quick example). Can anyone explain and give an example of an alternative to function-based iteration?

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  • Javascript: gradually adding to string in each iteration ?

    - by Kim Jong Woo
    I have a string like this that is split up: var tokens = "first>second>third>last".split(">"); What I would like in each iteration is for it to return Iteration 0: "last" Iteration 1: "third>last" Iteration 2: "second>third>last" Iteration 3: "first>second>third>last" I am thinking of using decrementing index for loop.... but is there a more efficient approach ? for (int w = tokens.length-1; w == 0; w--) { }

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  • Moving Forward with Code Iteration

    - by rcapote
    There are times when working on my programming projects, and I get to a point where I'm ready to move on to the next part of my program. However, when I sit down to implement this new feature I get stuck, in a sense. It's not that I don't know how to implement the feature, it's that I get stuck on figuring out the best way to implement said feature. So I sit back for a day or two and let the ideas ferment until I am comfortable with a design. I get worried that I may not write something as well as it could be, or that I might have to go back and rework the whole thing; so I put it off. This is a big reason why I've never really finished many personal projects. Anyone else experience this, and how do you keep your self moving forward in your project?

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