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• Effective and simple matching for 2 unequal small-scale point sets

  - by Pavlo Dyban

  I need to match two sets of 3D points, however the number of points in each set can be different. It seems that most algorithms are designed to align images and trimmed to work with hundreds of thousands of points. My case are 50 to 150 points in each of the two sets. So far I have acquainted myself with Iterative Closest Point and Procrustes Matching algorithms. Implementing Procrustes algorithms seems like a total overkill for this small quantity. ICP has many implementations, but I haven't found any readily implemented version accounting for the so-called "outliers" - points without a matching pair. Besides the implementation expense, algorithms like Fractional and Sparse ICP use some statistics information to cancel points that are considered outliers. For series with 50 to 150 points statistic measures are often biased or statistic significance criteria are not met. I know of Assignment Problem in linear optimization, but it is not suitable for cases with unequal sets of points. Are there other, small-scale algorithms that solve the problem of matching 2 point sets? I am looking for algorithm names, scientific papers or C++ implementations. I need some hints to know where to start my search.

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• How to manage Agile developers working with traditional (serial) business persons?

  - by Riggy

  Good afternoon, My work environment has some problems. Our IT team is trying to be more agile, but we're not really getting buy-in from the business. They attend our daily stand-ups and sprint reviews, and they help with sprint planning, but then they turn around and do 4 months of requirements gathering for a project before moving forward with a (mostly) serial development style. The sprint goals are things like "get XX% closer to release". For the IT team, they've turned the Sprints into a sort of death march. We end a Sprint one day and start a new Sprint the very next day. There's no reflection or changes done between sprints, only during. Having never done any of the agile methodologies before, I haven't had a very pleasant introduction to them. So my questions are: 1) Should there be some time (perhaps a week or so) between sprints to do the reflection/introspection/changes/etc.? Or are back-to-back-to-back sprints the norm? 2) Is there any chance for survival for an agile team with no agile business counter-parts? If not, are there some transitional methodologies or even tips for moving the business towards an iterative if not necessarily agile mindset? 3) Should your entire team be on every sprint? We have almost 20 programmers on a single sprint but working on completely different projects (typically teams of 3-5, sometimes larger). Is it normal to have a single sprint or should we be trying to manage multiple independent sprints? Should we be trying to keep the multiple sprints in concurrent lockstep or should their timetables be allowed to overlap and be flexible? Any thoughts or advice is appreciated. This is my first time coming over from SO for a question, so please let me know if there are better ways to phrase these kinds of questions (faq was rather helpful, but still not sure I'm following it perfectly). Thanks!

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• Scale an image with unscalable parts

  - by Uko

  Brief description of problem: imagine having some vector picture(s) and text annotations on the sides outside of the picture(s). Now the task is to scale the whole composition while preserving the aspect ratio in order to fit some view-port. The tricky part is that the text is not scalable only the picture(s). The distance between text and the image is still relative to the whole image, but the text size is always a constant. Example: let's assume that our total composition is two times larger than a view-port. Then we can just scale it by 1/2. But because the text parts are a fixed font size, they will become larger than we expect and won't fit in the view-port. One option I can think of is an iterative process where we repeatedly scale our composition until the delta between it and the view-port satisfies some precision. But this algorithm is quite costly as it involves working with the graphics and the image may be composed of a lot of components which will lead to a lot of matrix computations. What's more, this solution seems to be hard to debug, extend, etc. Are there any other approaches to solving this scaling problem?

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• glFramebufferTexture2D performance

  - by nornagon

  I'm doing heavy computation using the GPU, which involves a lot of render-to-texture operations. It's an iterative computation, so there's a lot of rendering to a texture, then rendering that texture to another texture, then rendering the second texture back to the first texture and so on, passing the texture through a shader each time. My question is: is it better to have a separate FBO for each texture I want to render into, or should I rather have one FBO and bind the target texture using glFramebufferTexture2D each time I want to change render target? My platform is OpenGL ES 2.0 on the iPhone.

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• Diophantine Equation

  - by swapnika

  Write an iterative program that finds the largest number of McNuggets that cannot be bought in exact quantity. Your program should print the answer in the following format (where the correct number is provided in place of n): "Largest number of McNuggets that cannot be bought in exact quantity: n" Hints: Hypothesize possible instances of numbers of McNuggets that cannot be purchased exactly, starting with 1 For each possible instance, called n, 1. Test if there exists non-negative integers a, b, and c, such that 6a+9b+20c = n. (This can be done by looking at all feasible combinations of a, b, and c) 2. If not, n cannot be bought in exact quantity, save n When you have found six consecutive values of n that in fact pass the test of having an exact solution, the last answer that was saved (not the last value of n that had a solution) is the correct answer, since you know by the theorem that any amount larger can also be bought in exact quantity

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• How to generate all variations with repetitions of a string?

  - by Svenstaro

  I want to generate all variations with repetitions of a string in C++ and I'd highly prefer a non-recursive algorithm. I've come up with a recursive algorithm in the past but due to the complexity (r^n) I'd like to see an iterative approach. I'm quite surprised that I wasn't able to find a solution to this problem anywhere on the web or on StackOverflow. I've come up with a Python script that does what I want as well: import itertools variations = itertools.product('ab', repeat=4) for variations in variations: variation_string = "" for letter in variations: variation_string += letter print variation_string Output: aaaa aaab aaba aabb abaa abab abba abbb baaa baab baba babb bbaa bbab bbba bbbb Ideally I'd like a C++ program that can produce the exact output, taking the exact same parameters. This is for learning purposes, it isn't homework. I wish my homework was like that.

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• SICP making change

  - by RyanD

  So; I'm a hobbiest who's trying to work through SICP (it's free!) and there is an example procedure in the first chapter that is meant to count the possible ways to make change with american coins; (change-maker 100) = 292. It's implemented something like: (define (change-maker amount) (define (coin-value n) (cond ((= n 1) 1) ((= n 2) 5) ((= n 3) 10) ((= n 4) 25) ((= n 5) 50))) (define (iter amount coin-type) (cond ((= amount 0) 1) ((or (= coin-type 0) (< amount 0)) 0) (else (+ (iter amount (- coin-type 1)) (iter (- amount (coin-value coin-type)) coin-type))))) (iter amount 5)) Anyway; this is a tree-recursive procedure, and the author "leaves as a challenge" finding an iterative procedure to solve the same problem (ie fixed space). I have not had luck figuring this out or finding an answer after getting frustrated. I'm wondering if it's a brain fart on my part, or if the author's screwing with me.

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• large amount of data in many text files - how to process?

  - by Stephen

  Hi, I have large amounts of data (a few terabytes) and accumulating... They are contained in many tab-delimited flat text files (each about 30MB). Most of the task involves reading the data and aggregating (summing/averaging + additional transformations) over observations/rows based on a series of predicate statements, and then saving the output as text, HDF5, or SQLite files, etc. I normally use R for such tasks but I fear this may be a bit large. Some candidate solutions are to 1) write the whole thing in C (or Fortran) 2) import the files (tables) into a relational database directly and then pull off chunks in R or Python (some of the transformations are not amenable for pure SQL solutions) 3) write the whole thing in Python Would (3) be a bad idea? I know you can wrap C routines in Python but in this case since there isn't anything computationally prohibitive (e.g., optimization routines that require many iterative calculations), I think I/O may be as much of a bottleneck as the computation itself. Do you have any recommendations on further considerations or suggestions? Thanks

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• How to optimize MATLAB loops?

  - by striglia

  I have been working lately on a number of iterative algorithms in MATLAB, and been getting hit hard by MATLAB's performance (or lack thereof) when it comes to loops. I'm aware of the benefit of vectorizing code when possible, but are there any tools for optimization when you need the loop for your algorithm? I am aware of the MEX-file option to write small subroutines in C/C++, although given my algorithms, this can be a very painful option given the data structures required. I mainly use MATLAB for the simplicity and speed of prototyping, so a syntactically complex, statically typed language is not ideal for my situation. Are there any other suggestions? Even other languages (python?) which have relatively painless matrix tools are an option.

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• Convert XML to table in SQL Server 2005.

  - by Tamim Sadikali

  If I pass in an xml parameter to a stored proc which looks like this: <ClientKeys> <ck>3052</ck> <ck>3051</ck> <ck>3050</ck> <ck>3049</ck> ... </ClientKeys> ...and then convert the XML to a temp table like this: CREATE TABLE #ClientKeys ( ClientKey varchar(36) ) INSERT INTO #ClientKeys (ClientKey) SELECT ParamValues.ck.value('.','VARCHAR(36)') FROM @ClientKeys.nodes('/ClientKeys/ck') as ParamValues(ck) ...the temp tbl is populated and everything is good. However the time taken to populate said table is strictly proportionate to the number of 'ck' elements in the xml - which I wasn't expecting as there is no iterative step. And thus the time taken to populate the tbl soon becomes 'too long'. Is there a quicker way to achieve the above?

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• Preventing Netbeans JAXB generation trashing classes

  - by Mac

  I'm developing a SOAP service using JAX-WS and JAXB under Netbeans 6.8, and getting a little frustrated with Netbeans trashing my work every time the XSD schema my JAXB bindings are based upon changes. To elaborate, the IDE automatically generates classes bound to the schema, which can then be (un)marshalled from/to XML using JAXB. To these classes I've added extra methods to (for example) convert to and from separate classes designed to be persisted to database with JPA. The problem is that whenever the schema changes and I rebuild, these classes are regenerated, and all my custom methods are deleted. I can manually replace them by copy-pasting from a backup file, but that is rather time-consuming and tedious. As I'm using an iterative design approach, the schema is changing rather frequently and I'm wasting an awful lot of time whenever it does, simply to reinstate my previous code. While the IDE automatically regenerating the JAXB-bound classes is entirely reasonable and I don't mean to imply otherwise, I was wondering if anyone had any bright ideas as to how to prevent my extra work having to be manually reinstated every time my schema changes?

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• Is there a better way to serially submit multiple AJAX requests?

  - by friedo

  I have a page with multiple forms that I submit via Ajax POSTs serially. At first, I tried using synchronous XHR requests, but this causes the browser to lock up for the duration of the request, and breaks my DOM-manipulation effects, which is unacceptable. So the pattern I ended up using is basically this: var fcount = 0; // incremented for each form to be submitted function submit_form( num ) { var fdata = { ... }; // data from form # num $.ajax( { async: true, url: '/index.cgi', data: fdata, type: 'POST', success: function() { if ( num < fcount ) { submit_form( ++num ); } } } ); } $( '#submit_form_btn' ).click( function() { submit_form( 1 ) } ); The recursion strikes me as a bit of an ugly solution to what is essentially an iterative problem. Is there a cleaner or more elegant way that this could be handled?

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• Avoding multiple thread spawns in pthreads

  - by madman

  Hi StackOverflow, I have an application that is parallellized using pthreads. The application has a iterative routine call and a thread spawn within the rountine (pthread_create and pthread_join) to parallelize the computation intensive section in the routine. When I use an instrumenting tool like PIN to collect the statistics the tool reports statistics for several threads(no of threads x no of iterations). I beleive it is because it is spawning new set of threads each time the routine is called. How can I ensure that I create the thread only once and all successive calls use the threads that have been created first. When I do the same with OpenMP and then try to collect the statistics, I see that the threads are created only once. Is it beacause of the OpenMP runtime ? Thanks.

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• How do we know the correct moves of Tower of Hanoi?

  - by Saqib

  We know that: In case of iterative solution: Alternating between the smallest and the next-smallest disks, follow the steps for the appropriate case: For an even number of disks: make the legal move between pegs A and B make the legal move between pegs A and C make the legal move between pegs B and C repeat until complete For an odd number of disks: make the legal move between pegs A and C make the legal move between pegs A and B make the legal move between pegs B and C repeat until complete In case of recursive solution: To move n discs from peg A to peg C: move n-1 discs from A to B. This leaves disc n alone on peg A move disc n from A to C move n-1 discs from B to C so they sit on disc n Now the questions are: How did we get this two solutions? Only by intuition? Or by logical/mathematical computation? If computation, how?

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• Free sounds for iPhone games.

  - by Roger Gilbrat

  I'm looking for a good source for sound effects for my iPhone game. I like SoundSnap, but they charge you for every sound you download, not just the ones you end up using. Sound design in games can be a very iterative process and I don't want to pay for 10 sounds I never use before finding the right one. freesound.org is another really good site, but they are all CC licensed and can't be used in commercial games. It's unclear if a free iPhone App is considered commercial (or if my final game will be free). Googling for this returns a huge number of pay sites with horrible web pages. I don't mind paying for sounds, but I want to pay for what I use. Any good personal recommendations?

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• optimized grid for rectangular items

  - by peterchen

  I have N rectangular items with an aspect ratio Aitem (X:Y). I have a rectangular display area with an aspect ratio Aview The items should be arranged in a table-like layout (i.e. r rows, c columns). what is the ideal grid rows x columns, so that individual items are largest? (rows * colums = N, of course - i.e. there may be "unused" grid places). A simple algorithm could iterate over rows = 1..N, calculate the required number of columns, and keep the row/column pair with the largest items. I wonder if there's a non-iterative algorithm, though (e.g. for Aitem = Aview = 1, rows / cols can be approximated by sqrt(N)).

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• Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

  - by Shane MacLaughlin

  Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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• Data frame linear fit in R

  - by user1247384

  This is perhaps a simple question, but I am n00b.Say I have a data frame with a bunch of columns. I need to call lm function over the column 1 and 2, 1 and 3, and so on. So basically I need to loop over all columns and store the results of the fit as I build the model. The problem I am running into is that lm(df[1]~df[2], data = df) doesnt work. In this case df is the data frame object and df[1] is the first column. What is a good way to do this in a loop, as in access the columns of df in an iterative fashion. Thanks.

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• Android -- Object Creation/Memory Allocation vs. Performance

  - by borg17of20

  Hello all, This is probably an easy one. I have about 20 TextViews/ImageViews in my current project that I access like this: ((TextView)multiLayout.findViewById(R.id.GameBoard_Multi_Answer1_Text)).setText(""); //or ((ImageView)multiLayout.findViewById(R.id.GameBoard_Multi_Answer1_Right)).setVisibility(View.INVISIBLE); My question is this, am I better off, from a performance standpoint, just assigning these object variables? Further, am I losing some performance to the constant "search" process that goes on as a part of the findViewById(...) method? (i.e. Does findsViewById(...) use some sort of hashtable/hashmap for look-ups or does it implement an iterative search over the view hierarchy?) At present, my program never uses more than 2.5MB of RAM, so will assigning 20 or so more object variables drastically affect this? I don't think so, but I figured I'd ask. Thanks.

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• Is there any Python library that allows me to parse an HTML document similar to what jQuery does?

  - by Sachin Tendulkar

  Is there any Python library that allows me to parse an HTML document similar to what jQuery does? i.e. I'd like to be able to use CSS selector syntax to grab an arbitrary set of nodes from the document, read their content/attributes, etc. The only Python HTML parsing lib I've used before was BeautifulSoup, and even though it's fine I keep thinking it would be faster to do my parsing if I had jQuery syntax available. :D Write an iterative program that finds the largest number of McNuggets that cannot be bought in exact quantity. Your program should print the answer in the following format (where the correct number is provided in place of n): "Largest number of McNuggets that cannot be bought in exact quantity: n"

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• Losing a programmer, what steps to take?

  - by Zak

  One of the programmers on our team is leaving for greener pastures. We will be going from 6 to 5. What steps should we take to ensure our development process continues to run smoothly, potentially while integrating in new blood. We are currently working on a short release cycle with iterative development. Design - code - review. The person leaving was the most senior dev on the team, and would often give lots of feedback to the rest of the team, especially during the design phase.

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• recursively reverse linked list.

  - by Amanda

  I am implementing a function to recursively reverse a linked-list, but getting seg-fault. typedef struct _node { int data; struct _node *next; } Node, *NodeP; NodeP recursiveReverseList(NodeP first){ if(first == NULL) return NULL; if(first->next == NULL) return head; NodeP rest = recursiveReverseList(head->next); rest->next = first; first->next = NULL; return first; } Can you please help. P.S. The iterative version is working fine though. Its not homework. Just practicing C.

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• Global variables in hadoop.

  - by Deepak Konidena

  Hi, My program follows a iterative map/reduce approach. And it needs to stop if certain conditions are met. Is there anyway i can set a global variable that can be distributed across all map/reduce tasks and check if the global variable reaches the condition for completion. Something like this. While(Condition != true){ Configuration conf = getConf(); Job job = new Job(conf, "Dijkstra Graph Search"); job.setJarByClass(GraphSearch.class); job.setMapperClass(DijkstraMap.class); job.setReducerClass(DijkstraReduce.class); job.setOutputKeyClass(IntWritable.class); job.setOutputValueClass(Text.class); } Where condition is a global variable that is modified during/after each map/reduce execution.

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• Best way to search a point across several polygons

  - by user1474341

  I have a requirement whereby I need to match a given point (lat,lon) against several polygons to decide if there is a match. The easiest way would be to iterative over each polygon and apply the point-in-polygon check algorithm, but that is prohibitively expensive. The next optimization that I did was to define a bounding rectangle for each polygon (upper bound, lower bound) and iteratively check the point against the bounding box (fewer comparisons as against checking all the points in the polygon). Is there any other optimization possible? Would a spatial index on the bound rectangle points or a geohash help ? Any guidance would be greatly appreciated. Thanks!

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• Segmentation fault in a function to reverse a singly linked list recursivley.

  - by Amanda

  I am implementing a function to recursively reverse a linked-list, but getting seg-fault. typedef struct _node { int data; struct _node *next; } Node, *NodeP; NodeP recursiveReverseList(NodeP first){ if(first == NULL) return NULL; if(first->next == NULL) return first; NodeP rest = recursiveReverseList(first->next); rest->next = first; first->next = NULL; return first; } Can you please help? P.S. The iterative version is working fine though. Its not homework. Just practicing C. Thank you all :)

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