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  • Matplotlib canvas drawing

    - by Morgoth
    Let's say I define a few functions to do certain matplotlib actions, such as def dostuff(ax): ax.scatter([0.],[0.]) Now if I launch ipython, I can load these functions and start a new figure: In [1]: import matplotlib.pyplot as mpl In [2]: fig = mpl.figure() In [3]: ax = fig.add_subplot(1,1,1) In [4]: run functions # run the file with the above defined function If I now call dostuff, then the figure does not refresh: In [6]: dostuff(ax) I have to then explicitly run: In [7]: fig.canvas.draw() To get the canvas to draw. Now I can modify dostuff to be def dostuff(ax): ax.scatter([0.],[0.]) ax.get_figure().canvas.draw() This re-draws the canvas automatically. But now, say that I have the following code: def dostuff1(ax): ax.scatter([0.],[0.]) ax.get_figure().canvas.draw() def dostuff2(ax): ax.scatter([1.],[1.]) ax.get_figure().canvas.draw() def doboth(ax): dostuff1(ax) dostuff2(ax) ax.get_figure().canvas.draw() I can call each of these functions, and the canvas will be redrawn, but in the case of doboth(), it will get redrawn multiple times. My question is: how could I code this, such that the canvas.draw() only gets called once? In the above example it won't change much, but in more complex cases with tens of functions that can be called individually or grouped, the repeated drawing is much more obvious, and it would be nice to be able to avoid it. I thought of using decorators, but it doesn't look as though it would be simple. Any ideas?

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  • Anyone got a nifty credit expiry algorithm?

    - by garethkeenan
    Our website uses a credit system to allow users to purchase inexpensive digital goods (eg. photos). We use credits, rather than asking the user to pay for items individually, because the items are cheap and we are trying to keep our credit-card/PayPal overhead low. Because we aren't a bank, we have to expire credits after a certain amount of time. We expire deposit credits after a year, but other types of credits (bonuses, prizes, refunds) may have a different shelf-life. When a buyer buys an item, we spend the credit that is going to expire first. Our current system keeps track of every deposit by storing the original value and the remainder to be spent. We keep a list of all purchases as well, of course. I am currently moving to a system which is much more like a traditional double-entry accounting system. A deposit will create a ledger item, increasing the user's 'spending' account balance. Every purchase will also create a ledger item, decreasing the user's 'spending' account balance. The new system has running balances, while the old system does not, which greatly improves our ability to find problems and do reconciliations. We do not want to use the old system of keeping a 'remainder' value attached to each deposit record because it is inefficient to replay a user's activities to calculate what the remainder of each deposit is over time (for the user's statement). So, after all of this verbose introduction, my question is "Does anyone else out there have a similar system of expiring credits?" If you could describe how you calculate expired credits it would be a great help. If all expired credits had the exact same shelf life, we would be able to calculate the expired amount using: Total Deposits - Total Spending - Deposits Not Due To Expire = Amount to Expire However, because deposits can have different shelf lives, this formula does not work because more than one deposit can be partially spent at any given time.

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  • FIlling a Java Bean tree structure from a csv flat file

    - by Clem
    Hi, I'm currently trying to construct a list of bean classes in Java from a flat description file formatted in csv. Concretely : Here is the structure of the csv file : MES_ID;GRP_PARENT_ID;GRP_ID;ATTR_ID M1 ; ;G1 ;A1 M1 ; ;G1 ;A2 M1 ;G1 ;G2 ;A3 M1 ;G1 ;G2 ;A4 M1 ;G2 ;G3 ;A5 M1 ; ;G4 ;A6 M1 ; ;G4 ;A7 M1 ; ;G4 ;A8 M2 ; ;G1 ;A1 M2 ; ;G1 ;A2 M2 ; ;G2 ;A3 M2 ; ;G2 ;A4 It corresponds to the hierarchical data structure : M1 ---G1 ------A1 ------A2 ------G2 ---------A3 ---------A4 ---------G3 ------------A5 ------G4 ---------A7 ---------A8 M2 ---G1 ------A1 ------A2 ---G2 ------A3 ------A4 Remarks : A message M can have an infinite number of groups G and attributes A A group G can have an infinite number of attributes and an infinite number of under-groups each of them having under-groups too That beeing said, I'm trying to read this flat csv decription to store it in this structure of beans : Map<String, MBean> messages = new HashMap<String, Mbean>(); == public class MBean { private String mes_id; private Map<String, GBean> groups; } public class GBean { private String grp_id; private Map<String, ABean> attributes; private Map<String, GBean> underGroups; } public class ABean { private String attr_id; } Reading the csv file sequentially is ok and I've been investigating how to use recursion to store the description data, but couldn't find a way. Thanks in advance for any of your algorithmic ideas. I hope it will put you in the mood of thinking about this ... I've to admit that I'm out of ideas :s

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  • how is google Calculator implemented ?

    - by AlgoMan
    When you search in Google "100F to C" how does it know to convert from Fahrenheit to Celsius. Similarly, conversion from different currencies and simple calculation. What is the data structure used. Or is it simple pattern matching the strings ?

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  • array interleaving problem

    - by Matt
    I was looking for something over the web when I came across this question. Have no idea of how to solve it. Help me out please. Suppose we have an array a1,a2,... ,an, b1,b2,..., bn How to change this array to a1,b1,a2,b2, ..., an,bn in O(n) time and in O(1) space.

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  • recursive function to get all the child categories

    - by user253530
    Here is what I'm trying to do: - i need a function that when passed as an argument an ID (for a category of things) will provide all the subcategories and the sub-sub categories and sub-sub-sub..etc. - i was thinking to use a recursive function since i don't know the number of subcategories their sub-subcategories and so on so here is what i've tried to do so far function categoryChild($id) { $s = "SELECT * FROM PLD_CATEGORY WHERE PARENT_ID = $id"; $r = mysql_query($s); if(mysql_num_rows($r) > 0) { while($row = mysql_fetch_array($r)) echo $row['ID'].",".categoryChild($row['ID']); } else { $row = mysql_fetch_array($r); return $row['ID']; } } If i use return instead of echo, i won't get the same result. I need some help in order to fix this or rewrite it from scratch

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  • How do bezier handles work?

    - by user146780
    On Wikipedia I found information about bezier curves and made a function to generate the inbetween points for a bezier polygon. I noticed that Expression Design uses bezier handles. This allows a circle to be made with 4 points each with a bezier handle. I'm just not sure mathematically how this works in relation with the formula for bezier point at time T. How do these handle vectors work to modify the shape? Basically what's there relation to the bezier formula? Thanks

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  • Stripe suppression algorithm needed

    - by maximus
    I have images with text. There are dark stripes in image that still exists in binary image too. That makes characters connected with that stripe - it can be vertical or horizontal (or at some angle) I need to remove them from image at first, and then to binarize. I've seen bandpass filter in ImageJ program that have some options like - suppress horizontal stripes, and it works good, but it also apply a bandpass filtering. So any idea please how to do it. I think it should be done in frequency domain.

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  • polynomial multiplication using fastfourier transform

    - by mawia
    i am going through the above topic from CLRS(CORMEN) (page 834) and I got stuck at this point. Can anybody please explain how the following expression, A(x)=A^{[0]}(x^2) +xA^{[1]}(x^2) follows from, n-1 ` S a_j x^j j=0 Where, A^{[0]} = a_0 + a_2x + a_4a^x ... a_{n-2}x^{\frac{n}{2-1}} A^{[1]} = a_1 + a_3x + a_5a^x ... a_{n-1}x^{\frac{n}{2-1}} WITH REGARDS THANKS

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  • Finding distance to the closest point in a point cloud on an uniform grid

    - by erik
    I have a 3D grid of size AxBxC with equal distance, d, between the points in the grid. Given a number of points, what is the best way of finding the distance to the closest point for each grid point (Every grid point should contain the distance to the closest point in the point cloud) given the assumptions below? Assume that A, B and C are quite big in relation to d, giving a grid of maybe 500x500x500 and that there will be around 1 million points. Also assume that if the distance to the nearest point exceds a distance of D, we do not care about the nearest point distance, and it can safely be set to some large number (D is maybe 2 to 10 times d) Since there will be a great number of grid points and points to search from, a simple exhaustive: for each grid point: for each point: if distance between points < minDistance: minDistance = distance between points is not a good alternative. I was thinking of doing something along the lines of: create a container of size A*B*C where each element holds a container of points for each point: define indexX = round((point position x - grid min position x)/d) // same for y and z add the point to the correct index of the container for each grid point: search the container of that grid point and find the closest point if no points in container and D > 0.5d: search the 26 container indices nearest to the grid point for a closest point .. continue with next layer until a point is found or the distance to that layer is greater than D Basically: put the points in buckets and do a radial search outwards until a points is found for each grid point. Is this a good way of solving the problem, or are there better/faster ways? A solution which is good for parallelisation is preferred.

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  • Mergesort : Revision

    - by stan
    Does merge sort work by; taking a list of values splitting it in to two take the first element of each list, the lowest value one goes in to a new list(and i guess removed from the original). comare the next two numbers - do this until one list is empty, then place the rest of the other list at the end ofthe nw list? Also, what are the ramifications of doing this on a linked list? Thanks

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  • Traveling Salesman - Nearest Neighbor vs Genetic DEATHMATCH

    - by EvilTeach
    Over the last few days I have noted a few web sites that demonstrated TS solution using genetic algorithms. I am looking for your opinion which is better for this particular problem. Heuristics vs Genetic. By better, I mean will yield a shorter/lower cost path. Explain why you feel the way that you do. Examples, and off-site links are welcome.

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  • What are the CS fundamentals behind package/dependency management?

    - by Frep D-Oronge
    Often I hear about situations where companies are developing extensable in house software (the dreaded enterprise 'framework') which is supposed to support multiple 'plugins' from diffirent teams. Usually this ends up being a half baked solution that does not really work due to compatibility prolems between addins, or between addins and the framework itself. Usually this means QA have to 'rubber stamp' a global set of versions accross all plugins, or more usually plugins are released and stuff breaks in nasty ways. This problem has been solved before however, for example the package management systems like apt for debian linux. I suspect that the reason it works is that it is built from the start on a known 'Computer Science-y' concept. My question is what is it?

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  • How to make ARGB transparency using bitwise operators.

    - by Smejda
    I need to make transparency, having 2 pixels: pixel1: {A, R, G, B} - foreground pixel pixel2: {A, R, G, B} - background pixel A,R,G,B are Byte values each color is represented by byte value now I'm calculating transparency as: newR = pixel2_R * alpha / 255 + pixel1_R * (255 - alpha) / 255 newG = pixel2_G * alpha / 255 + pixel1_G * (255 - alpha) / 255 newB = pixel2_B * alpha / 255 + pixel1_B * (255 - alpha) / 255 but it is too slow I need to do it with bitwise operators (AND,OR,XOR, NEGATION, BIT MOVE)

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  • Efficiently check string for one of several hundred possible suffixes

    - by Ghostrider
    I need to write a C/C++ function that would quickly check if string ends with one of ~1000 predefined suffixes. Specifically the string is a hostname and I need to check if it belongs to one of several hundred predefined second-level domains. This function will be called a lot so it needs to be written as efficiently as possible. Bitwise hacks etc anything goes as long as it turns out fast. Set of suffixes is predetermined at compile-time and doesn't change. I am thinking of either implementing a variation of Rabin-Karp or write a tool that would generate a function with nested ifs and switches that would be custom tailored to specific set of suffixes. Since the application in question is 64-bit to speed up comparisons I could store suffixes of up to 8 bytes in length as const sorted array and do binary search within it. Are there any other reasonable options?

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  • longest string in texts

    - by davit-datuashvili
    ok i have meet following problem too for example there is given two text find longest string that occur in both i think we should cretate string array where we should put common srings and then compare their length and which length will be largest print it is there fast method?

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  • longest string in texts

    - by davit-datuashvili
    Ihave following code in Java: import java.util.*; public class longest{ public static void main(String[] args){ int t=0;int m=0;int token1, token2; String words[]=new String[10]; String word[]=new String[10]; String common[]=new String[10]; String text="saqartvelo gabrwyindeba da gadzlierdeba aucileblad "; String text1="saqartvelo gamtliandeba da gadzlierdeba aucileblad"; StringTokenizer st=new StringTokenizer(text); StringTokenizer st1=new StringTokenizer(text1); token1=st.countTokens(); token2=st1.countTokens(); while (st.hasMoreTokens()){ words[t]=st.nextToken(); t++; } while (st1.hasMoreTokens()){ word[m]=st1.nextToken(); m++; } for (int k=0;k<token1;k++){ for (int f=0;f<token2;f++){ if (words[f].compareTo(word[f])==0){ common[f]=words[f]; } } } while (i<common.length){ System.out.println(common[i]); i++; } } } I want that in common array put elements which i in both text or these words saqartvelo (georgia in english) da (and in english) gadzlierdeba (will be stronger) aucileblad (sure) and then between these words find string which has maximum length but it does not work more correctly it show me these words and also many null elements. How do I correct it?

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  • best way to pick a random subset from a collection?

    - by Tom
    I have a set of objects in a Vector from which I'd like to select a random subset (e.g. 100 items coming back; pick 5 randomly). In my first (very hasty) pass I did an extremely simple and perhaps overly clever solution: Vector itemsVector = getItems(); Collections.shuffle(itemsVector); itemsVector.setSize(5); While this has the advantage of being nice and simple, I suspect it's not going to scale very well, i.e. Collections.shuffle() must be O(n) at least. My less clever alternative is Vector itemsVector = getItems(); Random rand = new Random(System.currentTimeMillis()); // would make this static to the class List subsetList = new ArrayList(5); for (int i = 0; i < 5; i++) { // be sure to use Vector.remove() or you may get the same item twice subsetList.add(itemsVector.remove(rand.nextInt(itemsVector.size()))); } Any suggestions on better ways to draw out a random subset from a Collection?

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  • How to find the longest continuous subsequence whose reverse is also a subsequence

    - by iecut
    Suppose I have a sequence x1,x2,x3.....xn, and I want to find the longest continuous subsequence xi,xi+1,xi+2......xi+k, whose reverse is also a subsequence of the given sequence. And if there are multiple such subsequences, then I also have to find the first. ex:- consider the sequences: abcdefgedcg here i=3 and k=2 aabcdddd here i=5, k=3 I tried looking at the original longest common subsequence problem, but that is used to compare the two sequences to find the longest common subsequence.... but here is only one sequence from which we have to find the subsequences. Please let me know what is the best way to approach this problem, to find the optimal solution.

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  • Is regex too slow? Real life examples where simple non-regex alternative is better

    - by polygenelubricants
    I've seen people here made comments like "regex is too slow!", or "why would you do something so simple using regex!" (and then present a 10+ lines alternative instead), etc. I haven't really used regex in industrial setting, so I'm curious if there are applications where regex is demonstratably just too slow, AND where a simple non-regex alternative exists that performs significantly (maybe even asymptotically!) better. Obviously many highly-specialized string manipulations with sophisticated string algorithms will outperform regex easily, but I'm talking about cases where a simple solution exists and significantly outperforms regex. What counts as simple is subjective, of course, but I think a reasonable standard is that if it uses only String, StringBuilder, etc, then it's probably simple.

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  • Compiler optimization of references

    - by Phineas
    I often use references to simplify the appearance of code: vec3f& vertex = _vertices[index]; // Calculate the vertex position vertex[0] = startx + col * colWidth; vertex[1] = starty + row * rowWidth; vertex[2] = 0.0f; Will compilers recognize and optimize this so it is essentially the following? _vertices[index][0] = startx + col * colWidth; _vertices[index][1] = starty + row * rowWidth; _vertices[index][2] = 0.0f;

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  • Extend base type and automatically update audit information on Entity

    - by Nix
    I have an entity model that has audit information on every table (50+ tables) CreateDate CreateUser UpdateDate UpdateUser Currently we are programatically updating audit information. Ex: if(changed){ entity.UpdatedOn = DateTime.Now; entity.UpdatedBy = Environment.UserName; context.SaveChanges(); } But I am looking for a more automated solution. During save changes, if an entity is created/updated I would like to automatically update these fields before sending them to the database for storage. Any suggestion on how i could do this? I would prefer to not do any reflection, so using a text template is not out of the question. A solution has been proposed to override SaveChanges and do it there, but in order to achieve this i would either have to use reflection (in which I don't want to do ) or derive a base class. Assuming i go down this route how would I achieve this? For example EXAMPLE_DB_TABLE CODE NAME --Audit Tables CREATE_DATE CREATE_USER UPDATE_DATE UPDATE_USER And if i create a base class public abstract class IUpdatable{ public virtual DateTime CreateDate {set;} public virtual string CreateUser { set;} public virtual DateTime UpdateDate { set;} public virtual string UpdateUser { set;} } The end goal is to be able to do something like... public overrride void SaveChanges(){ //Go through state manager and update audit infromation //FOREACH changed entity in state manager if(entity is IUpdatable){ //If state is created... update create audit. //if state is updated... update update audit } } But I am not sure how I go about generating the code that would extend the interface.

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  • OOP vs PP for algorithms

    - by Ilian
    Which paradigm is better for design and analysis of algorithms? Which is faster? Because I have a subject called Design and Analysis of Algorithms in university and have a time limit for programs. Is OOP slower than Procedure programming? Or the time difference is not big?

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