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  • Google App Engine Database Index

    - by fjsj
    I need to store a undirected graph in a Google App Engine database. For optimization purposes, I am thinking to use database indexes. Using Google App Engine, is there any way to define the columns of a database table to create its index? I will need some optimization, since my app uses this stored undirected graph on a content-based filtering for item recommendation. Also, the recommender algorithm updates the weights of some graph's edges. If it is not possible to use database indexes, please suggest another method to reduce query time for the graph table. I believe my algorithm does more data retrieval operations from graph table than write operations. PS: I am using Python.

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  • Marching squares: Finding multiple contours within one source field?

    - by TravisG
    Principally, this is a follow-up-question to a problem from a few weeks ago, even though this is about the algorithm in general without application to my actual problem. The algorithm basically searches through all lines in the picture, starting from the top left of it, until it finds a pixel that is a border. In pseudo-C++: int start = 0; for(int i=0; i<amount_of_pixels; ++i) { if(pixels[i] == border) { start = i; break; } } When it finds one, it starts the marching squares algorithm and finds the contour to whatever object the pixel belongs to. Let's say I have something like this: Where everything except the color white is a border. And have found the contour points of the first blob: For the general algorithm it's over. It found a contour and has done its job. How can I move on to the other two blobs to find their contours as well?

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  • Design pattern: static function call with input/output containers?

    - by Pavlo Dyban
    I work for a company in software research department. We use algorithms from our real software and wrap them so that we can use them for prototyping. Every time an algorithm interface changes, we need to adapt our wrappers respectively. Recently all algorithms have been refactored in such a manner that instead of accepting many different inputs and returning outputs via referenced parameters, they now accept one input data container and one output data container (the latter is passed by reference). Algorithm interface is limited to a static function call like that: class MyAlgorithm{ static bool calculate(MyAlgorithmInput input, MyAlgorithmOutput &output); } This is actually a very powerful design, though I have never seen it in a C++ programming environment before. Changes in the number of parameters and their data types are now encapsulated and they don't change the algorithm callback. In the latest algorithm which I have developed I used the same scheme. Now I want to know if this is a popular design pattern and what it is called.

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  • Is the Leptonica implementation of 'Modified Median Cut' not using the median at all?

    - by TheCodeJunkie
    I'm playing around a bit with image processing and decided to read up on how color quantization worked and after a bit of reading I found the Modified Median Cut Quantization algorithm. I've been reading the code of the C implementation in Leptonica library and came across something I thought was a bit odd. Now I want to stress that I am far from an expert in this area, not am I a math-head, so I am predicting that this all comes down to me not understanding all of it and not that the implementation of the algorithm is wrong at all. The algorithm states that the vbox should be split along the lagest axis and that it should be split using the following logic The largest axis is divided by locating the bin with the median pixel (by population), selecting the longer side, and dividing in the center of that side. We could have simply put the bin with the median pixel in the shorter side, but in the early stages of subdivision, this tends to put low density clusters (that are not considered in the subdivision) in the same vbox as part of a high density cluster that will outvote it in median vbox color, even with future median-based subdivisions. The algorithm used here is particularly important in early subdivisions, and 3is useful for giving visible but low population color clusters their own vbox. This has little effect on the subdivision of high density clusters, which ultimately will have roughly equal population in their vboxes. For the sake of the argument, let's assume that we have a vbox that we are in the process of splitting and that the red axis is the largest. In the Leptonica algorithm, on line 01297, the code appears to do the following Iterate over all the possible green and blue variations of the red color For each iteration it adds to the total number of pixels (population) it's found along the red axis For each red color it sum up the population of the current red and the previous ones, thus storing an accumulated value, for each red note: when I say 'red' I mean each point along the axis that is covered by the iteration, the actual color may not be red but contains a certain amount of red So for the sake of illustration, assume we have 9 "bins" along the red axis and that they have the following populations 4 8 20 16 1 9 12 8 8 After the iteration of all red bins, the partialsum array will contain the following count for the bins mentioned above 4 12 32 48 49 58 70 78 86 And total would have a value of 86 Once that's done it's time to perform the actual median cut and for the red axis this is performed on line 01346 It iterates over bins and check they accumulated sum. And here's the part that throws me of from the description of the algorithm. It looks for the first bin that has a value that is greater than total/2 Wouldn't total/2 mean that it is looking for a bin that has a value that is greater than the average value and not the median ? The median for the above bins would be 49 The use of 43 or 49 could potentially have a huge impact on how the boxes are split, even though the algorithm then proceeds by moving to the center of the larger side of where the matched value was.. Another thing that puzzles me a bit is that the paper specified that the bin with the median value should be located, but does not mention how to proceed if there are an even number of bins.. the median would be the result of (a+b)/2 and it's not guaranteed that any of the bins contains that population count. So this is what makes me thing that there are some approximations going on that are negligible because of how the split actually takes part at the center of the larger side of the selected bin. Sorry if it got a bit long winded, but I wanted to be as thoroughas I could because it's been driving me nuts for a couple of days now ;)

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  • How can I find out how much memory an object (rather the instance of an object) of a C++ class consu

    - by Shadow
    Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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  • How can I find out how much memory an object of a C++ class consumes?

    - by Shadow
    Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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  • In a C++ template, is it allowed to return an object with spesific type parameters?

    - by nieldw
    When I've got a template with certain type parameters, is it allowed for a function to return an object of this same template, but with different types? In other words, is the following allowed? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { /* Construct new Graph with apropriate decorators */ Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); /* ... */ return span; }; If this is not allowed, how can I accomplish the same kind of thing?

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  • How can I find out how much memory an instance of a C++ class consumes?

    - by Shadow
    Hi, I am developing a Graph-class, based on boost-graph-library. A Graph-object contains a boost-graph, so to say an adjacency_list, and a map. When monitoring the total memory usage of my program, it consumes quite a lot (checked with pmap). Now, I would like to know, how much of the memory is exactly consumed by a filled object of this Graph-class? With filled I mean when the adjacency_list is full of vertices and edges. I found out, that using sizeof() doesn't bring me far. Using valgrind is also not an alternative as there is quite some memory allocation done previously and this makes the usage of valgrind impractical for this purpose. I'm also not interested in what other parts of the program cost in memory, I want to focus on one single object. Thank you.

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  • How to plot the graph(line) from a file in java?

    - by kiran
    I have a directory containing list of files. Those files have some list of values as x and y ordered as line by line. And my question is just I would like to read those files one by one and to plot line graphs based on those values. Could you please help me for that?

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  • In a C++ template, is it allowed to return an object with specific type parameters?

    - by nieldw
    When I've got a template with certain type parameters, is it allowed for a function to return an object of this same template, but with different types? In other words, is the following allowed? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { /* Construct new Graph with apropriate decorators */ Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); /* ... */ return span; }; If this is not allowed, how can I accomplish the same kind of thing?

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  • Optimizing processing and management of large Java data arrays

    - by mikera
    I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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  • Generic Event Generator and Handler from User Supplied Types?

    - by JaredBroad
    I'm trying to allow the user to supply custom data and manage the data with custom types. The user's algorithm will get time synchronized events pushed into the event handlers they define. I'm not sure if this is possible but here's the "proof of concept" code I'd like to build. It doesn't detect T in the for loop: "The type or namespace name 'T' could not be found" class Program { static void Main(string[] args) { Algorithm algo = new Algorithm(); Dictionary<Type, string[]> userDataSources = new Dictionary<Type, string[]>(); // "User" adding custom type and data source for algorithm to consume userDataSources.Add(typeof(Weather), new string[] { "temperature data1", "temperature data2" }); for (int i = 0; i < 2; i++) { foreach (Type T in userDataSources.Keys) { string line = userDataSources[typeof(T)][i]; //Iterate over CSV data.. var userObj = new T(line); algo.OnData < typeof(T) > (userObj); } } } //User's algorithm pattern. interface IAlgorithm<TData> where TData : class { void OnData<TData>(TData data); } //User's algorithm. class Algorithm : IAlgorithm<Weather> { //Handle Custom User Data public void OnData<Weather>(Weather data) { Console.WriteLine(data.date.ToString()); Console.ReadKey(); } } //Example "user" custom type. public class Weather { public DateTime date = new DateTime(); public double temperature = 0; public Weather(string line) { Console.WriteLine("Initializing weather object with: " + line); date = DateTime.Now; temperature = -1; } } }

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  • Cooperative linux vs vm

    - by Rhythmic Algorithm
    What are the advantages / disadvantages of using cooperative linux like portable ubuntu for example compared to a qemu or any other virtual machine installation. Is one option notably faster than the other plus and other things that should be taken into consideration.

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  • How to stop RAID5 array while it is shown to be busy?

    - by RCola
    I have a raid5 array and need to stop it, but while trying to stop it getting error. # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sde1[3](F) sdc1[4](F) sdf1[2] sdd1[1] 2120320 blocks level 5, 32k chunk, algorithm 2 [3/2] [_UU] unused devices: <none> # mdadm --stop mdadm: metadata format 00.90 unknown, ignored. mdadm: metadata format 00.90 unknown, ignored. mdadm: No devices given. # mdadm --stop /dev/md0 mdadm: metadata format 00.90 unknown, ignored. mdadm: metadata format 00.90 unknown, ignored. mdadm: fail to stop array /dev/md0: Device or resource busy and # lsof | grep md0 md0_raid5 965 root cwd DIR 8,1 4096 2 / md0_raid5 965 root rtd DIR 8,1 4096 2 / md0_raid5 965 root txt unknown /proc/965/exe # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sde1[3](F) sdc1[4](F) sdf1[2] sdd1[1] 2120320 blocks level 5, 32k chunk, algorithm 2 [3/2] [_UU] # grep md0 /proc/mdstat md0 : active raid5 sde1[3](F) sdc1[4](F) sdf1[2] sdd1[1] # grep md0 /proc/partitions 9 0 2120320 md0 While booting, md1 is mounted ok but md0 failed for some unknown reason # dmesg | grep md[0-9] [ 4.399658] raid5: allocated 3179kB for md1 [ 4.400432] raid5: raid level 5 set md1 active with 3 out of 3 devices, algorithm 2 [ 4.400678] md1: detected capacity change from 0 to 2121793536 [ 4.403135] md1: unknown partition table [ 38.937932] Filesystem "md1": Disabling barriers, trial barrier write failed [ 38.941969] XFS mounting filesystem md1 [ 41.058808] Ending clean XFS mount for filesystem: md1 [ 46.325684] raid5: allocated 3179kB for md0 [ 46.327103] raid5: raid level 5 set md0 active with 2 out of 3 devices, algorithm 2 [ 46.330620] md0: detected capacity change from 0 to 2171207680 [ 46.335598] md0: unknown partition table [ 46.410195] md: recovery of RAID array md0 [ 117.970104] md: md0: recovery done. # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid5 sde1[0] sdf1[2] sdd1[1] 2120320 blocks level 5, 32k chunk, algorithm 2 [3/3] [UUU] md1 : active raid5 sdc2[0] sdf2[2] sde2[3](S) sdd2[1] 2072064 blocks level 5, 128k chunk, algorithm 2 [3/3] [UUU]

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  • P values in wilcox.test gone mad :(

    - by Error404
    I have a code that isn't doing what it should do. I am testing P value for a wilcox.test for a huge set of data. the code i am using is the following library(MASS) data1 <- read.csv("file1path.csv",header=T,sep=",") data2 <- read.csv("file2path.csv",header=T,sep=",") data3 <- read.csv("file3path.csv",header=T,sep=",") data4 <- read.csv("file4path.csv",header=T,sep=",") data1$K <- with(data1,{"N"}) data2$K <- with(data2,{"E"}) data3$K <- with(data3,{"M"}) data4$K <- with(data4,{"U"}) new=rbind(data1,data2,data3,data4) i=3 for (o in 1:4800){ x1 <- data1[,i] x2 <- data2[,i] x3 <- data3[,i] x4 <- data4[,i] wt12 <- wilcox.test(x1,x2, na.omit=TRUE) wt13 <- wilcox.test(x1,x3, na.omit=TRUE) wt14 <- wilcox.test(x1,x4, na.omit=TRUE) if (wt12$p.value=="NaN"){ print("This is wrong") } else if (wt12$p.value < 0.05){ print(wt12$p.value) mypath=file.path("C:", "all1-less-05", (paste("graph-data1-data2",names(data1[i]), ".pdf", sep="-"))) pdf(file=mypath) mytitle = paste("graph",names(data1[i])) boxplot(new[,i] ~ new$K, main = mytitle, names.arg=c("data1","data2","data3","data4")) dev.off() } if (wt13$p.value=="NaN"){ print("This is wrong") } else if (wt13$p.value < 0.05){ print(wt13$p.value) mypath=file.path("C:", "all2-less-05", (paste("graph-data1-data3",names(data1[i]), ".pdf", sep="-"))) pdf(file=mypath) mytitle = paste("graph",names(data1[i])) boxplot(new[,i] ~ new$K, main = mytitle, names.arg=c("data1","data2","data3","data4")) dev.off() } if (wt14$p.value=="NaN"){ print("This is wrong") } else if (wt14$p.value < 0.05){ print(wt14$p.value) mypath=file.path("C:", "all3-less-05", (paste("graph-data1-data4",names(data1[i]), ".pdf", sep="-"))) pdf(file=mypath) mytitle = paste("graph",names(data1[i])) boxplot(new[,i] ~ new$K, main = mytitle, names.arg=c("data1","data2","data3","data4")) dev.off() } i=i+1 } I am having 2 problems with this long command: 1- Without specifying a certain P value, the code gives me arouind 14,000 graphs, when specifying a p value less than 0.05 the number of graphs generated goes down to 9,0000. THE FIRST PROBLEM IS: Some P value are more than 0.05 and are still showing up! 2- I designed the program to give me a result of "This is wrong" when the Value of P is "NaN", I am getting results of "NaN" Here's a screenshot from the results do you know what the mistake i made with the command to get these errors? Thanks in advance

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  • Representing complex object dependencies

    - by max
    I have several classes with a reasonably complex (but acyclic) dependency graph. All the dependencies are of the form: class X instance contains an attribute of class Y. All such attributes are set during initialization and never changed again. Each class' constructor has just a couple parameters, and each object knows the proper parameters to pass to the constructors of the objects it contains. class Outer is at the top of the dependency hierarchy, i.e., no class depends on it. Currently, the UI layer only creates an Outer instance; the parameters for Outer constructor are derived from the user input. Of course, Outer in the process of initialization, creates the objects it needs, which in turn create the objects they need, and so on. The new development is that the a user who knows the dependency graph may want to reach deep into it, and set the values of some of the arguments passed to constructors of the inner classes (essentially overriding the values used currently). How should I change the design to support this? I could keep the current approach where all the inner classes are created by the classes that need them. In this case, the information about "user overrides" would need to be passed to Outer class' constructor in some complex user_overrides structure. Perhaps user_overrides could be the full logical representation of the dependency graph, with the overrides attached to the appropriate edges. Outer class would pass user_overrides to every object it creates, and they would do the same. Each object, before initializing lower level objects, will find its location in that graph and check if the user requested an override to any of the constructor arguments. Alternatively, I could rewrite all the objects' constructors to take as parameters the full objects they require. Thus, the creation of all the inner objects would be moved outside the whole hierarchy, into a new controller layer that lies between Outer and UI layer. The controller layer would essentially traverse the dependency graph from the bottom, creating all the objects as it goes. The controller layer would have to ask the higher-level objects for parameter values for the lower-level objects whenever the relevant parameter isn't provided by the user. Neither approach looks terribly simple. Is there any other approach? Has this problem come up enough in the past to have a pattern that I can read about? I'm using Python, but I don't think it matters much at the design level.

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  • How to get compatibility between C# and SQL2k8 AES Encryption?

    - by Victor Rodrigues
    I have an AES encryption being made on two columns: one of these columns is stored at a SQL Server 2000 database; the other is stored at a SQL Server 2008 database. As the first column's database (2000) doesn't have native functionality for encryption / decryption, we've decided to do the cryptography logic at application level, with .NET classes, for both. But as the second column's database (2008) allow this kind of functionality, we'd like to make the data migration using the database functions to be faster, since the data migration in SQL 2k is much smaller than this second and it will last more than 50 hours because of being made at application level. My problem started at this point: using the same key, I didn't achieve the same result when encrypting a value, neither the same result size. Below we have the full logic in both sides.. Of course I'm not showing the key, but everything else is the same: private byte[] RijndaelEncrypt(byte[] clearData, byte[] Key) { var memoryStream = new MemoryStream(); Rijndael algorithm = Rijndael.Create(); algorithm.Key = Key; algorithm.IV = InitializationVector; var criptoStream = new CryptoStream(memoryStream, algorithm.CreateEncryptor(), CryptoStreamMode.Write); criptoStream.Write(clearData, 0, clearData.Length); criptoStream.Close(); byte[] encryptedData = memoryStream.ToArray(); return encryptedData; } private byte[] RijndaelDecrypt(byte[] cipherData, byte[] Key) { var memoryStream = new MemoryStream(); Rijndael algorithm = Rijndael.Create(); algorithm.Key = Key; algorithm.IV = InitializationVector; var criptoStream = new CryptoStream(memoryStream, algorithm.CreateDecryptor(), CryptoStreamMode.Write); criptoStream.Write(cipherData, 0, cipherData.Length); criptoStream.Close(); byte[] decryptedData = memoryStream.ToArray(); return decryptedData; } This is the SQL Code sample: open symmetric key columnKey decryption by password = N'{pwd!!i_ll_not_show_it_here}' declare @enc varchar(max) set @enc = dbo.VarBinarytoBase64(EncryptByKey(Key_GUID('columnKey'), 'blablabla')) select LEN(@enc), @enc This varbinaryToBase64 is a tested sql function we use to convert varbinary to the same format we use to store strings in the .net application. The result in C# is: eg0wgTeR3noWYgvdmpzTKijkdtTsdvnvKzh+uhyN3Lo= The same result in SQL2k8 is: AI0zI7D77EmqgTQrdgMBHAEAAACyACXb+P3HvctA0yBduAuwPS4Ah3AB4Dbdj2KBGC1Dk4b8GEbtXs5fINzvusp8FRBknF15Br2xI1CqP0Qb/M4w I just didn't get yet what I'm doing wrong. Do you have any ideas? EDIT: One point I think is crucial: I have one Initialization Vector at my C# code, 16 bytes. This IV is not set at SQL symmetric key, could I do this? But even not filling the IV in C#, I get very different results, both in content and length.

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  • how to create a wind rose in excel 2007

    - by Patrick
    I am attempting to create a wind rose graph (i.e.- here or here). My data is wind speed and cardinal wind direction in separate columns: Wind (mph) Wind Direction 3.66 SE 2.69 SE 2.62 SW 2.76 SW 2.11 NW 3.13 NW 3.55 SW 3.62 W My final goal is to actually create the graph with a VBA macro, but I am unsure how to even create the graph manually. I can, if need be, convert the cardinal directions to degrees. Any help is greatly appreciated

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  • ganglia graphs like munin for cpu, etc?

    - by CarpeNoctem
    I'm coming from munin and a CPU graph contains data for system, user, nice, etc ALL on one graph. I just installed ganglia and setup the basic monitoring. It appears that each type of cpu data is a separate graph! WTF is this and can I change the defaults to combine these into a single per host? That is my question, how do I combine cpu data into a single graph. Also, can I change the layout to something closer to munin's day-week side-by-side layout? I'm trying to be impartial and give ganglia a chance. ;)

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  • Annotating Graphs From Textual Data

    - by steven
    I've got a graph that was generated from a data set that contains: (date, value, annotation) The annotation is a constant value [its either there or is blank] and I would like to add in the third bit of data into the graph I have. An example of this is in the image. The blue line is a graph of the (date, value) graph, and I would like to add in the red dots as graphing (date, annotation@value). Is there an easy way to do this in excel, without having to modify the appearance of the data?

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