Search Results

Search found 585 results on 24 pages for 'numerical equations'.

Page 22/24 | < Previous Page | 18 19 20 21 22 23 24  | Next Page >

• What are some ways to accomplish a dynamic array?

  - by Ted

  I'm going to start working on a new game and one of the things I'd like to accomplish is a dynamic array sort of system that would hold map data. The game will be top-down 2d and made with XNA 4.0 and C#. You will begin in a randomized area which will essentially be tile based. As such a 2 dimensional array would be one way to accomplish this by holding numerical values which would correspond to a list of textures and that would be how it would draw this randomly created map. The problem is I would kind of only like to create the area around where you start and they could venture in which ever direction they wanted to. This would mean I'd have to populate the map array with more randomized data in the direction they go. I could make a really large array and use the center of it and the rest would be in anticipation of new content to be made, but that just seems very inefficient. I suppose when they start a new game I could have a one time map creation process that would go through and create a large randomly generated map array, but holding all of in memory at all times seems also inefficient. Perhaps if there was a way that I'd only hold parts of that map data in memory at one time and somehow not hold the rest in memory. In the end I only need to have a chunk of the map somewhat close to them in memory so perhaps some of you might have suggestions on good ways to approach this kind of randomized map and dynamic array problem. It wouldn't need to be a dynamic array type of thing if I made it so that it pulled in map data nearby that is needed and then once off the screen and not needed it could somehow get rid of that memory that way I wouldn't have a huge array taking up a bunch of memory.

  Read the article

• method works fine, until it is called in a function, then UnboundLocalError

  - by user1776100

  I define a method called dist, to calculate the distance between two points which I does it correctly when directly using the method. However, when I get a function to call it to calculate the distance between two points, I get UnboundLocalError: local variable 'minkowski_distance' referenced before assignment edit sorry, I just realised, this function does work. However I have another method calling it that doesn't. I put the last method at the bottom This is the method: class MinkowskiDistance(Distance): def __init__(self, dist_funct_name_str = 'Minkowski distance', p=2): self.p = p def dist(self, obj_a, obj_b): distance_to_power_p=0 p=self.p for i in range(len(obj_a)): distance_to_power_p += abs((obj_a[i]-obj_b[i]))**(p) minkowski_distance = (distance_to_power_p)**(1/p) return minkowski_distance and this is the function: (it basically splits the tuples x and y into their number and string components and calculates the distance between the numeric part of x and y and then the distance between the string parts, then adds them. def total_dist(x, y, p=2, q=2): jacard = QGramDistance(q=q) minkowski = MinkowskiDistance(p=p) x_num = [] x_str = [] y_num = [] y_str = [] #I am spliting each vector into its numerical parts and its string parts so that the distances #of each part can be found, then summed together. for i in range(len(x)): if type(x[i]) == float or type(x[i]) == int: x_num.append(x[i]) y_num.append(y[i]) else: x_str.append(x[i]) y_str.append(y[i]) num_dist = minkowski.dist(x_num,y_num) str_dist = I find using some more steps #I am simply adding the two types of distance to get the total distance: return num_dist + str_dist class NearestNeighbourClustering(Clustering): def __init__(self, data_file, clust_algo_name_str='', strip_header = "no", remove = -1): self.data_file= data_file self.header_strip = strip_header self.remove_column = remove def run_clustering(self, max_dist, p=2, q=2): K = {} #dictionary of clusters data_points = self.read_data_file() K[0]=[data_points[0]] k=0 #I added the first point in the data to the 0th cluster #k = number of clusters minus 1 n = len(data_points) for i in range(1,n): data_point_in_a_cluster = "no" for c in range(k+1): distances_from_i = [total_dist(data_points[i],K[c][j], p=p, q=q) for j in range(len(K[c]))] d = min(distances_from_i) if d <= max_dist: K[c].append(data_points[i]) data_point_in_a_cluster = "yes" if data_point_in_a_cluster == "no": k += 1 K[k]=[data_points[i]] return K

  Read the article

• 6 Interesting Facts About NASA’s Mars Rover ‘Curiosity’

  - by Gopinath

  Humans quest for exploring the surrounding planets to see whether we can live there or not is taking new shape today. NASA’s Mars probing robot, Curiosity, blasted off today on its 9 months journey to reach Mars and explore it for the possibilities of life there. Scientist says that Curiosity is one most advanced rover ever launched to probe life on other planets. Here is the launch video and some analysis by a news reporter Lets look at the 6 interesting facts about the mission 1. It’s as big as a car Curiosity is the biggest ever rover ever launched by NASA to probe life on outer planets. It’s as big as a car and almost double the size of its predecessor rover Spirit. The length of Curiosity is around 9 feet 10 inches(3 meters), width is 9 feet 1 inch (2.8 meters) and height is 7 feet (2.1 meters). 2. Powered by Plutonium – Lasts 24×7 for 23 months The earlier missions of NASA to explore Mars are powered by Solar power and that hindered capabilities of the rovers to move around when the Sun is hiding. Due to dependency of Sun the earlier rovers were not able to traverse the places where there is no Sun light. Curiosity on the other hand is equipped with a radioisotope power system that generates electricity from the heat emitted by plutonium’s radioactive decay. The plutonium weighs around 10 pounds and can generate power required for operating the rover close to 23 weeks. The best part of the new power system is, Curiosity can roam around in darkness, light and all year around. 3. Rocket powered backpack for a science fiction style landing The Curiosity is so heavy that NASA could not use parachute and balloons to air-drop the rover on the surface of Mars like it’s previous missions. They are trying out a new science fiction style air-dropping mechanism that is similar to sky crane heavy-lift helicopter. The landing of the rover begins first with entry into the Mars atmosphere protected by a heat shield. At about 6 miles to the surface, the heat shield is jettisoned and a parachute is deployed to glide the rover smoothly. When the rover touches 3 miles above the surface, the parachute is jettisoned and the eight motors rocket backpack is used for a smooth and impact free landing as shown in the image. Here is an animation created by NASA on the landing sequence. If you are interested in getting more detailed information about the landing process check this landing sequence picture available on NASA website 4. Equipped with Star Wars style laser gun Hollywood movie directors and novelist always imagined aliens coming to earth with spaceships full of laser guns and blasting the objects which comes on their way. With Curiosity the equations are going to change. It has a powerful laser gun equipped in one of it’s arms to beam laser on rocks to vaporize them. This is not part of any assault mission Curiosity is expected to carry out, the laser gun is will be used to carry out experiments to detect life and understand nature. 5. Most sophisticated laboratory powered by 10 instruments Around 10 state of art instruments are part of Curiosity rover and the these 10 instruments form a most advanced rover based lab ever built by NASA. There are instruments to cut through rocks to examine them and other instruments will search for organic compounds. Mounted cameras can study targets from a distance, arm mounted instruments can study the targets they touch. Microscopic lens attached to the arm can see and magnify tiny objects as tiny as 12.5 micro meters. 6. Rover Carrying 1.24 million names etched on silicon Early June 2009 NASA launched a campaign called “Send Your Name to Mars” and around 1.24 million people registered their names through NASA’s website. All those 1.24 million names are etched on Silicon chips mounted onto Curiosity’s deck. If you had registered your name in the campaign may be your name is going to reach Mars soon. Curiosity On Web If you wish to follow the mission here are few links to help you NASA’s Curiosity Web Page Follow Curiosity on Facebook Follow @MarsCuriosity on Twitter Artistic Gallery Image of Mars Rover Curiosity A printable sheet of Curiosity Mission [pdf] Images credit: NASA This article titled,6 Interesting Facts About NASA’s Mars Rover ‘Curiosity’, was originally published at Tech Dreams. Grab our rss feed or fan us on Facebook to get updates from us.

  Read the article

• Determining the angle to fire a shot when target and shooter moves, and bullet moves with shooter velocity added in

  - by Azaral

  I saw this question: Predicting enemy position in order to have an object lead its target and followed the link in the answer to stack overflow. In the stack overflow page I used the 2nd answer, the one that is a large mathematical derivation. My situation is a little different though. My first question though is will the answer provided in the stack overflow page even work to begin with, assuming the original circumstances of moving target and stationary shooter. My situation is a little different than that situation. My target moves, the shooter moves, and the bullets from the shooter start off with the velocities in x and y added to the bullets' x and y velocities. If you are sliding to the right, the bullets will remain in front of you as you move so as long as your velocity remains constant. What I'm trying to do is to get the enemy to be able to determine where they need to shoot in order to hit the player. Unless the player and enemy is stationary, the velocity from the ship adding to the velocity of the bullets will cause a miss. I'd rather like to prevent that. I used the formula in the stack overflow answer and did what I thought were the appropriate adjustments. I've been banging at this for the last four hours and I just can't make it click. It is probably something really simple and boneheaded that I am missing (that seems to be a lot of my problems lately). Here is the solution presented from the stack overflow answer: It boils down to solving a quadratic equation of the form: a * sqr(x) + b * x + c == 0 Note that by sqr I mean square, as opposed to square root. Use the following values: a := sqr(target.velocityX) + sqr(target.velocityY) - sqr(projectile_speed) b := 2 * (target.velocityX * (target.startX - cannon.X) + target.velocityY * (target.startY - cannon.Y)) c := sqr(target.startX - cannon.X) + sqr(target.startY - cannon.Y) Now we can look at the discriminant to determine if we have a possible solution. disc := sqr(b) - 4 * a * c If the discriminant is less than 0, forget about hitting your target -- your projectile can never get there in time. Otherwise, look at two candidate solutions: t1 := (-b + sqrt(disc)) / (2 * a) t2 := (-b - sqrt(disc)) / (2 * a) Note that if disc == 0 then t1 and t2 are equal. If there are no other considerations such as intervening obstacles, simply choose the smaller positive value. (Negative t values would require firing backward in time to use!) Substitute the chosen t value back into the target's position equations to get the coordinates of the leading point you should be aiming at: aim.X := t * target.velocityX + target.startX aim.Y := t * target.velocityY + target.startY Here is my code, after being corrected by Sam Hocevar (thank you again for your help!). It still doesn't work. For some reason it never enters the section of code inside the if(disc = 0) (obviously because it is always less than zero but...). However, if I plug the numbers from my game log on the enemy and player positions and velocities it outputs a valid firing solution. I have looked at the code side by side a couple of times now and I can't find any differences. There has got to be something simple I'm missing here. If someone else could look at this code and determine what is going on here I'd appreciate it. I know it's not going through that section because if it were, shouldShoot would become true and the enemy would be blasting away at the player. This section calls the function in question, CalculateShootHeading() if(shouldMove) { UseEngines(); } x += xVelocity; y += yVelocity; CalculateShootHeading(); if(shouldShoot) { ShootWeapons(); } UpdateWeapons(); This is CalculateShootHeading(). This is inside the enemy class so x and y are the enemy's x and y and the same with velocity. One output from my game log gives Player X = 2108, Player Y = -180.956, Player X velocity = 10.9949, Player Y Velocity = -6.26017, Enemy X = 1988.31, Enemy Y = -339.051, Enemy X velocity = 1.81666, Enemy Y velocity = -9.67762, 0 enemy projectiles. The output from the console tester is Bullet position = 2210.49, -239.313 and Player Position = 2210.49, -239.313. This doesn't make any sense. The only thing that could be different is the code or the input into my function in the game and I've checked that and I don't think that it is wrong as it's updated before this and never changed. float const bulletSpeed = 30.f; float const dx = playerX - x; float const dy = playerY - y; float const vx = playerXVelocity - xVelocity; float const vy = playerYVelocity - yVelocity; float const a = vx * vx + vy * vy - bulletSpeed * bulletSpeed; float const b = 2.f * (vx * dx + vy * dy); float const c = dx * dx + dy * dy; float const disc = b * b - 4.f * a * c; shouldShoot = false; if (disc >= 0.f) { float t0 = (-b - std::sqrt(disc)) / (2.f * a); float t1 = (-b + std::sqrt(disc)) / (2.f * a); if (t0 < 0.f || (t1 < t0 && t1 >= 0.f)) { t0 = t1; } if (t0 >= 0.f) { float shootx = vx + dx / t0; float shooty = vy + dy / t0; heading = std::atan2(shooty, shootx) * RAD2DEGREE; } shouldShoot = true; }

  Read the article

• Runge-Kutta (RK4) integration for game physics

  - by Kai

  Gaffer on Games has a great article about using RK4 integration for better game physics. The implementation is straightforward but the math behind it confuses me. I understand derivatives and integrals on a conceptual level but I haven't manipulated equations in a long time. Here's the brunt of Gaffer's implementation: void integrate(State &state, float t, float dt) { Derivative a = evaluate(state, t, 0.0f, Derivative()); Derivative b = evaluate(state, t+dt*0.5f, dt*0.5f, a); Derivative c = evaluate(state, t+dt*0.5f, dt*0.5f, b); Derivative d = evaluate(state, t+dt, dt, c); const float dxdt = 1.0f/6.0f * (a.dx + 2.0f*(b.dx + c.dx) + d.dx); const float dvdt = 1.0f/6.0f * (a.dv + 2.0f*(b.dv + c.dv) + d.dv) state.x = state.x + dxdt * dt; state.v = state.v + dvdt * dt; } Can anybody explain in simple terms how RK4 works? Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? After reading the accepted answer below, and several other articles, I have a grasp on how RK4 works. To answer my own questions: Can anybody explain in simple terms how RK4 works? RK4 takes advantage of the fact that we can get a much better approximation of a function if we use its higher-order derivatives rather than just the first or second derivative. That's why the Taylor series converges much faster than Euler approximations. (take a look at the animation on the right side of that page) Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? The Runge-Kutta method is an approximation of a function that samples derivatives of several points within a timestep, unlike the Taylor series which only samples derivatives of a single point. After sampling these derivatives we need to know how to weigh each sample to get the closest approximation possible. An easy way to do this is to pick constants that coincide with the Taylor series, which is how the constants of a Runge-Kutta equation are determined. This article made it clearer for me: http://web.mit.edu/10.001/Web/Course%5FNotes/Differential%5FEquations%5FNotes/node5.html. Notice how (15) is the Taylor series expansion while (17) is the Runge-Kutta derivation. How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? Mathematically it converges much faster than doing many Euler approximations. Of course, with enough Euler approximations we can gain equal accuracy to RK4, but the computational power needed doesn't justify using Euler.

  Read the article

• average velocity, as3

  - by VideoDnd

  Hello, I need something accurate I can plug equations in to if you can help. How would you apply the equation bellow? Thanks guys. AVERAGE VELOCITY AND DISPLACEMENT average velocity V=X/T displacement x=v*T more info example I have 30 seconds and a field that is 170 yards. What average velocity would I need my horse to travel at to reach the end of the field in 30 seconds. I moved the decimal places around and got this. Here's what I tried 'the return value is close, but not close enough' FLA here var TIMER:int = 10; var T:int = 0; var V:int = 5.6; var X:int = 0; var Xf:int = 17000/10*2; var timer:Timer = new Timer(TIMER,Xf); timer.addEventListener(TimerEvent.TIMER, incrementCounter); timer.start(); function formatCount(i:int):String { var fraction:int = Math.abs(i % 100); var whole:int = Math.abs(i / 100); return ("0000000" + whole).substr(-7, 7) + "." + (fraction < 10 ? "0" + fraction : fraction); } function incrementCounter(event:TimerEvent) { T++; X = Math.abs(V*T); text.text = formatCount(X); } tests TARGET 5.6yards * 30seconds = 168yards INTEGERS 135.00 in 30 seconds MATH.ROUND 135.00 in 30 seconds NUMBERS 140.00 in 30 seconds control timer 'I tested with this and the clock on my desk' var timetest:Timer = new Timer(1000,30); var Dplus:int = 17000; timetest.addEventListener(TimerEvent.TIMER, cow); timetest.start(); function cow(evt:TimerEvent):void { tx.text = String("30 SECONDS: " + timetest.currentCount); if(timetest.currentCount> Dplus){ timetest.stop(); } } //far as I got...couldn't get delta to work... T = (V*timer.currentCount); X += Math.round(T);

  Read the article

• C# Extend array type to overload operators

  - by Episodex

  I'd like to create my own class extending array of ints. Is that possible? What I need is array of ints that can be added by "+" operator to another array (each element added to each), and compared by "==", so it could (hopefully) be used as a key in dictionary. The thing is I don't want to implement whole IList interface to my new class, but only add those two operators to existing array class. I'm trying to do something like this: class MyArray : Array<int> But it's not working that way obviously ;). Sorry if I'm unclear but I'm searching solution for hours now... UPDATE: I tried something like this: class Zmienne : IEquatable<Zmienne> { public int[] x; public Zmienne(int ilosc) { x = new int[ilosc]; } public override bool Equals(object obj) { if (obj == null || GetType() != obj.GetType()) { return false; } return base.Equals((Zmienne)obj); } public bool Equals(Zmienne drugie) { if (x.Length != drugie.x.Length) return false; else { for (int i = 0; i < x.Length; i++) { if (x[i] != drugie.x[i]) return false; } } return true; } public override int GetHashCode() { int hash = x[0].GetHashCode(); for (int i = 1; i < x.Length; i++) hash = hash ^ x[i].GetHashCode(); return hash; } } Then use it like this: Zmienne tab1 = new Zmienne(2); Zmienne tab2 = new Zmienne(2); tab1.x[0] = 1; tab1.x[1] = 1; tab2.x[0] = 1; tab2.x[1] = 1; if (tab1 == tab2) Console.WriteLine("Works!"); And no effect. I'm not good with interfaces and overriding methods unfortunately :(. As for reason I'm trying to do it. I have some equations like: x1 + x2 = 0.45 x1 + x4 = 0.2 x2 + x4 = 0.11 There are a lot more of them, and I need to for example add first equation to second and search all others to find out if there is any that matches the combination of x'es resulting in that adding. Maybe I'm going in totally wrong direction?

  Read the article

• Converting numbers to their language, how?

  - by SoLoGHoST

  Ok, I'm using mathematical equations to output numbers, though, I need this to be compatible for all languages. Currently, all language strings are within a php array called $txt, and each key of the array gets called for that language. I'm outputting the following: Column 1, Column 2, Column 3, and so on, as well as Row 1, Row 2, Row 3, and so on. The calculations are done via php and javascript, so I'm wondering on the best approach for how to support all languages for the numbers only. I don't do the translations, someone else does, but I need to be able to point it to, either the php variable $txt of where the language is defined, or, since the calculations are done via javascript also, I need to somehow store this in there. I'm thinking of storing something like this: // This part goes in the php language file. $txt['0'] = '0'; $txt['1'] = '1'; $txt['2'] = '2'; $txt['2'] = '3'; $txt['4'] = '4'; $txt['5'] = '5'; $txt['6'] = '6'; $txt['7'] = '7'; $txt['8'] = '8'; $txt['9'] = '9'; // This part goes in the php file that needs to call the numbers. echo '<script> var numtxts = new Array(); numtxts[0] = \'', $txt['0'], '\'; numtxts[1] = \'', $txt['1'], '\'; numtxts[2] = \'', $txt['2'], '\'; numtxts[3] = \'', $txt['3'], '\'; numtxts[4] = \'', $txt['4'], '\'; numtxts[5] = \'', $txt['5'], '\'; numtxts[6] = \'', $txt['6'], '\'; numtxts[7] = \'', $txt['7'], '\'; numtxts[8] = \'', $txt['8'], '\'; numtxts[9] = \'', $txt['9'], '\'; </script>'; And than in the javascript function it could grab the correct string for each number like so: // Example Number String below. var numString = "10"; var transNum = ""; for(x=0;x<numString.length;x++) { var numChar = numString.charAt(x); transNum += numtxts[parseInt(numChar)]; } return transNum; The problem with this bit of code is that it groups the numbers, not sure if all languages do that, like the english language does...? Perhaps there's a better approach for this? Can anyone help please? Thanks :)

  Read the article

• How to localize numerals?

  - by SoLoGHoST

  Ok, I'm using mathematical equations to output numbers, though, I need this to be compatible for all languages. Currently, all language strings are within a php array called $txt, and each key of the array gets called for that language. I'm outputting the following: Column 1, Column 2, Column 3, and so on, as well as Row 1, Row 2, Row 3, and so on. The calculations are done via php and javascript, so I'm wondering on the best approach for how to support all languages for the numbers only. I don't do the translations, someone else does, but I need to be able to point it to, either the php variable $txt of where the language is defined, or, since the calculations are done via javascript also, I need to somehow store this in there. I'm thinking of storing something like this: // This part goes in the php language file. $txt['0'] = '0'; $txt['1'] = '1'; $txt['2'] = '2'; $txt['2'] = '3'; $txt['4'] = '4'; $txt['5'] = '5'; $txt['6'] = '6'; $txt['7'] = '7'; $txt['8'] = '8'; $txt['9'] = '9'; // This part goes in the php file that needs to call the numbers. echo '<script> var numtxts = new Array(); numtxts[0] = \'', $txt['0'], '\'; numtxts[1] = \'', $txt['1'], '\'; numtxts[2] = \'', $txt['2'], '\'; numtxts[3] = \'', $txt['3'], '\'; numtxts[4] = \'', $txt['4'], '\'; numtxts[5] = \'', $txt['5'], '\'; numtxts[6] = \'', $txt['6'], '\'; numtxts[7] = \'', $txt['7'], '\'; numtxts[8] = \'', $txt['8'], '\'; numtxts[9] = \'', $txt['9'], '\'; </script>'; And than in the javascript function it could grab the correct string for each number like so: // Example Number String below. var numString = "10"; var transNum = ""; for(x=0;x<numString.length;x++) { var numChar = numString.charAt(x); transNum += numtxts[parseInt(numChar)]; } return transNum; The problem with this bit of code is that it groups the numbers, not sure if all languages do that, like the english language does...? Perhaps there's a better approach for this? Can anyone help please? Thanks :)

  Read the article

• No more memory available in Mathematica, Fit the parameters of system of differential equation

  - by user1058051

  I encountered a memory problem in Mathematica, when I tried to process my experimental data. It's a system of two differential equations and I need to find most suitable parameters. Unfortunately I am not a Pro in Mathematica, so the program used a lot of memory, when the parameter epsilon is more than 0.4. When it less than 0.4, the program work properly. The command 'historylength = 0' and attempts to reduce the Accuracy Goal and WorkingPrecision didn`t help. I can't use ' clear Cache ', because there isnt a circle. I'm trying to understand what mistakes I made, and how I may limit the memory usage. I have already bought extra-RAM, now its 4GB, and now I haven't free memory-slots in motherboard Remove["Global`*"]; T=13200; L = 0.085; e = 0.41; v = 0.000557197; q = 0.1618; C0 = 0.0256; R = 0.00075; data = {{L,600,0.141124587},{L,1200,0.254134509},{L,1800,0.342888644}, {L,2400,0.424476295},{L,3600,0.562844542},{L,4800,0.657111356}, {L,6000,0.75137817},{L,7200,0.815876516},{L,8430,0.879823594}, {L,9000,0.900771775},{L,13200,1}}; model[(De_)?NumberQ, (Kf_)?NumberQ, (Y_)?NumberQ] := model[De, Kf, Y] = yeld /.Last[Last[ NDSolve[{ v (Ci^(1,0))[z,t]+(Ci^(0,1))[z,t]== -((3 (1-e) Kf (Ci[z,t]-C0))/ (R e (1-(R Kf (1-R/r[z,t]))/De))), (r^(0,1))[z,t]== (R^2 Kf (Ci[z,t]-C0))/ (q r[z,t]^2 (1-(R Kf (1-R/r[z,t]))/De)), (yeld^(0,1))[z,t]== Y*(v e Ci[z,t])/(L q (1-e)), r[z,0]==R, Ci[z,0]==0, Ci[0,t]==0, yeld[z,0]==0}, {r[z,t],Ci[z,t],yeld},{z,0,L},{t,0,T}]]] fit = FindFit[data, {model[De, Kf, Y][z, t], {Y > 0.97, Y < 1.03, Kf > 10^-6, Kf < 10^-4, De > 10^-13, De < 10^-9}}, {{De,7*10^-13}, {Kf, 10^-5}, {Y, 1}}, {z, t}, Method -> NMinimize] data = {{600,0.141124587},{1200,0.254134509},{1800,0.342888644}, {2400,0.424476295},{3600,0.562844542},{4800,0.657111356}, {6000,0.75137817},{7200,0.815876516},{8430,0.879823594}, {9000,0.900771775},{13200,1}}; YYY = model[ De /. fit[[1]], Kf /. fit[[2]], Y /. fit[[3]]]; Show[Plot[Evaluate[YYY[L,t]],{t,0,T},PlotRange->All], ListPlot[data,PlotStyle->Directive[PointSize[Medium],Red]]] the link on the .nb file http://www.4shared.com/folder/249TSjlz/_online.html

  Read the article

• Extending QuickBooks Reporting with the QuickBooks ADO.NET Data Provider

  - by dataintegration

  The ADO.NET Provider for QuickBooks comes with several reports you may request from QuickBooks by default. However, there are many more that are not readily available. The ADO.NET Provider for QuickBooks makes it easy for you to create new reports and customize existing ones. In this article, we will illustrate how to create your own report and retrieve it from the Server Explorer in Visual Studio. For this example we will show how to create an Item Profitability Report. Creating the report script file Step 1: Download the sample reports available here. Extract them to a folder of your choice. Step 2: Make a copy of the ReportGeneralSummary.rsd file and rename it to ItemProfitability.rsd. Then open the file in any text editor. Step 3: Open the installation directory of the ADO.NET Provider for QuickBooks. Under the \db\ folder, locate the ReportJob.rsb file. Open this file in another text editor. Note: Although we are using ReportJob.rsb for this example, other reports may be contained in other Report*.rsb files. We recommend consulting the included help file and first locating the Report stored procedure and ReportType you are looking for. Otherwise, you may open each Report*.rsb file and look under the "reporttype" input for the report you are attempting to create. Step 4: First, let's rename the title of ItemProfitability.rsd. Near the top of the file you will see a title and description. Change the title to match the name of the file. Change the description to anything you like. For example: <rsb:info title="ItemProfitability" description="Executes my custom report."> Just below the Title, there are a number of columns. The Id represents the row number. The RowType represents the type of data returned by QuickBooks. The ColumnValue* columns represent all of the column data returned by QuickBooks. In some instances, we may need to add additional ColumnValue columns. Step 5: To add additional ColumnValue columns, simply copy the last column, paste it directly below, and continue increasing the numerical value at end of the attribute name. For example: <attr name="ColumnValue9" xs:type="string" readonly="true" required="false" desc="Represents a column of data."/> <attr name="ColumnValue10" xs:type="string" readonly="true" required="false" desc="Represents a column of data."/> <attr name="ColumnValue11" xs:type="string" readonly="true" required="false" desc="Represents a column of data."/> <attr name="ColumnValue12" xs:type="string" readonly="true" required="false" desc="Represents a column of data."/> ... Caution: Do not rename the ColumnValue* definitions themselves. They are generalized so that we can understand each type of report returned by QuickBooks. Renaming them to something other than ColumnValue* will cause your columns to return with null values. Step 6: Now let's update the available inputs for the table. From the ReportJob.rsb file, copy all of the input elements into ItemProfitability under the "Psuedo-Column definitions" comment. You will be replacing the existing input elements in ItemProfitability with inputs from ReportJob. When you are done, it should look like this: <!-- Psuedo-Column definitions --> <input name="reporttype" description="The type of the report." value="ITEMESTIMATESVSACTUALS,ITEMPROFITABILITY,JOBESTIMATESVSACTUALSDETAIL,JOBESTIMATESVSACTUALSSUMMARY,JOBPROFITABILITYDETAIL,JOBPROFITABILITYSUMMARY," default="ITEMESTIMATESVSACTUALS" /> <input name="reportperiod" description="Report date range in the format (fromdate:todate), and either value may be omitted for an open ended range (e.g. 2009-12-25:). Supported date format: yyyy-MM-dd." /> <input name="reportdaterangemacro" description="Use a predefined date range." value="ALL,TODAY,THISWEEK,THISWEEKTODATE,THISMONTH,THISMONTHTODATE,THISQUARTER,THISQUARTERTODATE,THISYEAR,THISYEARTODATE,YESTERDAY,LASTWEEK,LASTWEEKTODATE,LASTMONTH,LASTMONTHTODATE,LASTQUARTER,LASTQUARTERTODATE,LASTYEAR,LASTYEARTODATE,NEXTWEEK,NEXTFOURWEEKS,NEXTMONTH,NEXTQUARTER,NEXTYEAR," default="ALL" /> ... Step 7: Now let's update the operationname attribute. This needs to match the same operationname used by ReportJob. After you have copied the correct value from ReportJob.rsb, the operationname in ItemProfitability should look like so: <rsb:set attr="operationname" value="qbReportJob"/> Step 8: There is one more thing we can do to make this a true Item Profitability report. We can remove the reporttype input and hardcode the value. To do this, copy and paste the rsb:set used for operationname. Then rename the attr and value to match the name and value you want to use. For example: <rsb:set attr="operationname" value="qbReportJob"/> <rsb:set attr="reporttype" value="ITEMPROFITABILITY"/> After this you can remove the input for reporttype. Now that you have your own report file, we can move on to displaying the report in the Visual Studio server explorer. Accessing the report through the Data Provider Step 1: Open Visual Studio. In the Server Explorer, configure a new connection with the QuickBooks Data Provider. Step 2: For the Location connection string property, enter the directory where the new report has been saved to. Step 3: The new report should appear as a new view in the Server Explorer. Let's retrieve data from it. Step 4: You can specify any inputs in the WHERE clause. New Report Example Script To help you get started using this new QuickBooks Data Provider report, you will need to download the QuickBooks ADO.NET Data Provider and the fully functional sample script.

  Read the article

• Dynamic DataGrid columns in WPF DataGrid based on the underlying set of data (and their type)

  - by StatsMan

  Hello everyone, I've got kind of a conceptual question. I am in the process of wrapping some statistics classes I wrote into WPF. For that I have two DataGrid(-Views, currently in WinForms). In one DataGrid each row represents a column in the other. There I can set-up different variables (as in mathematical/statistical variables) with fields like "Header", "DataType", "ValidationBehaviour", "DisplayType". There I can also set-up how it should be displayed. Some Columns can automatically be set to ComboBoxColumns, some TextBoxColumns, and so on and so forth. So, now once I've set-up these Columns I can go to the other grid and enter my data. I may, for instance, have generated (in grid 1) one Column called "Annual Gross Salary" with input of numerical values. Another Column called "Education" with "0=NoEducation", "1=College Level", "3=Universitary" etc. These labels are displayed as text in the combobox and my statistics engine behind then selects the respective value (0-3) for calculations (i.e. ordinal, nominal variables). Sooo. In WinForms I could basically generate all the columns by hand in code and then add my data in the respective cells/rows. Now in WPF I thought that must be easy to realise. However, yesterday I got started with ICustomPropertyDescriptor which (maybe I was too thick) didn't give me the results I was looking for. Basically, I just need to be able to dynamically generate columns (and rows) with different Layout, Controls (ComboBox, simple Input, DateTimes) based on the data that I have. But I don't really know how to go about it? So here in summary: DataGrid 1 Purpose is to display columns that have been specified in DataGrid 2 In rows, the user can add any kind of data in the rows below the columns that is allowed as to the columns specifications DataGrid 2 Each row in this grid represents a column in DataGrid 1 Contains fields like Name/Header, DataType, Validation Behaviour, Default Value, Data Formatting, etc. Also contains a function to be able to set-up how it should be displayed. The user can select from, for instance, ComboBoxColumn (and also add the available options), DateTime, normal TextBox, CheckBox etc. After finishing adding a row it will automatically appear as a new column in DataGrid 1 I'd appreciate any kind of pointer into the right direction. Thanks very, very much in advance! :)

  Read the article

• delta-dictionary/dictionary with revision awareness in python?

  - by shabbychef

  I am looking to create a dictionary with 'roll-back' capabilities in python. The dictionary would start with a revision number of 0, and the revision would be bumped up only by explicit method call. I do not need to delete keys, only add and update key,value pairs, and then roll back. I will never need to 'roll forward', that is, when rolling the dictionary back, all the newer revisions can be discarded, and I can start re-reving up again. thus I want behaviour like: >>> rr = rev_dictionary() >>> rr.rev 0 >>> rr["a"] = 17 >>> rr[('b',23)] = 'foo' >>> rr["a"] 17 >>> rr.rev 0 >>> rr.roll_rev() >>> rr.rev 1 >>> rr["a"] 17 >>> rr["a"] = 0 >>> rr["a"] 0 >>> rr[('b',23)] 'foo' >>> rr.roll_to(0) >>> rr.rev 0 >>> rr["a"] 17 >>> rr.roll_to(1) Exception ... Just to be clear, the state associated with a revision is the state of the dictionary just prior to the roll_rev() method call. thus if I can alter the value associated with a key several times 'within' a revision, and only have the last one remembered. I would like a fairly memory-efficient implementation of this: the memory usage should be proportional to the deltas. Thus simply having a list of copies of the dictionary will not scale for my problem. One should assume the keys are in the tens of thousands, and the revisions are in the hundreds of thousands. We can assume the values are immutable, but need not be numeric. For the case where the values are e.g. integers, there is a fairly straightforward implementation (have a list of dictionaries of the numerical delta from revision to revision). I am not sure how to turn this into the general form. Maybe bootstrap the integer version and add on an array of values? all help appreciated.

  Read the article

• How to best design a date/geographic proximity query on GAE?

  - by Dane

  Hi all, I'm building a directory for finding athletic tournaments on GAE with web2py and a Flex front end. The user selects a location, a radius, and a maximum date from a set of choices. I have a basic version of this query implemented, but it's inefficient and slow. One way I know I can improve it is by condensing the many individual queries I'm using to assemble the objects into bulk queries. I just learned that was possible. But I'm also thinking about a more extensive redesign that utilizes memcache. The main problem is that I can't query the datastore by location because GAE won't allow multiple numerical comparison statements (<,<=,=,) in one query. I'm already using one for date, and I'd need TWO to check both latitude and longitude, so it's a no go. Currently, my algorithm looks like this: 1.) Query by date and select 2.) Use destination function from geopy's distance module to find the max and min latitude and longitudes for supplied distance 3.) Loop through results and remove all with lat/lng outside max/min 4.) Loop through again and use distance function to check exact distance, because step 2 will include some areas outside the radius. Remove results outside supplied distance (is this 2/3/4 combination inefficent?) 5.) Assemble many-to-many lists and attach to objects (this is where I need to switch to bulk operations) 6.) Return to client Here's my plan for using memcache.. let me know if I'm way out in left field on this as I have no prior experience with memcache or server caching in general. -Keep a list in the cache filled with "geo objects" that represent all my data. These have five properties: latitude, longitude, event_id, event_type (in anticipation of expanding beyond tournaments), and start_date. This list will be sorted by date. -Also keep a dict of pointers in the cache which represent the start and end indices in the cache for all the date ranges my app uses (next week, 2 weeks, month, 3 months, 6 months, year, 2 years). -Have a scheduled task that updates the pointers daily at 12am. -Add new inserts to the cache as well as the datastore; update pointers. Using this design, the algorithm would now look like: 1.) Use pointers to slice off appropriate chunk of list based on supplied date. 2-4.) Same as above algorithm, except with geo objects 5.) Use bulk operation to select full tournaments using remaining geo objects' event_ids 6.) Assemble many-to-manys 7.) Return to client Thoughts on this approach? Many thanks for reading and any advice you can give. -Dane

  Read the article

• Git/Mercurial (hg) opinion

  - by Richard

  First, let me say I'm not a professional programmer, but an engineer who had a need for it and had to learn. I was always working alone, so it was just me and my seven splitted personalities ... and we worked okey as a team :) Most of my stuff is done in C/Fortran/Matlab and so far I've been learning git to manage it all. However, although I've had no unsolvable problems with it, I've never been "that" happy with it ... for everything I cannot do, I hae to look up a book. And, for some time now I've been hearning a lot of good stuff about hg. Now, a coleague of mine will have to work with me on a project (I almost feel sorry for him) and he's started learning hg (says he likes it more), and I'm considering the switch myself. We work almost exclusivly on Windows platform (although I manage relatively ok using unix tools and things that come from that part of the world). So, I was wondering, in a described scenario, what problems could I expect with the switch. I heard that hg is rather more user friendly towards windows users, regarding the user interfaces. How does it handle repositories ? Does it create them the same way as git does (just one subdirectory in a working directory) and can I just copy the whole project directory (including git repo) and just carry them somewhere with no extra thinking ? (I really liked that when I was choosing over git/svn). Are there any good books on it that you can recommend (something like Pro Git, only for Hg). What are good ways to implement hg into Visual Studio/GVim for Windows, or into Windows Explorer so I can work relatively easily (I would like to avoid using the command line for everything regarding it, like in git shell). Is there something else I should be aware of (please, on this don't point me to other questions ... they just give me a ton of info, and I'm not sure what is it that I should take as important, and what to disregard). I'm trying to cut some time, since I cannot spend all that time relearning hg, like I did for git. I've also heard git is c project, while mercurial is python ... is there any noticeable difference in speed. git was pretty speedy ... will I encounter some waiting while working. Notice: All my projects are of let's say, middle size ... mostly numerical simulations ... 10-15000 lines (medium size?)

  Read the article

• jQuery, get datas in AJAX (done) then, display them as star (error)

  - by Tristan

  Hello, In my website, there are 2 steps : I get values from another domain with AJAX, it's numbers 100% working Then, i want to display those numbers in stars with this plugin (http://stackoverflow.com/questions/1987524/turn-a-number-into-star-rating-display-using-jquery-and-css) The error : the stars plugin does not work for the value i recieve from my ajax request, but it's working for my values for my domain which are not JS manipulated you can see a demo here http://www.esl.eu/fr/test/test_atome/?killcache=true PS: the data in ajax are provided in JSON-P so i wrote a parser which look like this: jQuery.ajax({ type: "get", dataType: "jsonp", url: "http://www.foo.com/", data: {demandeur: "monkey" }, cache: true, success: function(data, textStatus, XMLHttpRequest){ var obj = null, length = data.length; for (var i = 0; i < length; i++) { widget = "<p>AVERAGES<p>"; widget += "<p><span class='stars'>"; widget += data[i].services; widget += "</span></p>"; widget += "<p><span class='stars'>"; widget += data[i].qualite; widget += "</span></p>"; jQuery('#gotserv').html(widget); } } }); }); Then i have the star plugin after this function : $.fn.stars = function() { $(this).each(function() { // Get the value var val = parseFloat($(this).html()); // Make sure that the value is in 0 - 5 range val = val 5 ? 5 : (val < 0 ? 0 : val); // Calculate physical size var size = 16 * val; // Create stars holder var stars = $(''); // Adjust yellow stars' width stars.find('span').width(size); // Replace the numerical value with stars $(this).replaceWith(stars); }); I hope you understand, i don't know if i'm clear Thank you

  Read the article

• How to designing a generic databse whos layout may change over time?

  - by mawg

  Here's a tricky one - how do I programatically create and interrogate a database who's contents I can't really foresee? I am implementing a generic input form system. The user can create PHP forms with a WYSIWYG layout and use them for any purpose he wishes. He can also query the input. So, we have three stages: a form is designed and generated. This is a one-off procedure, although the form can be edited later. This designs the database. someone or several people make use of the form - say for daily sales reports, stock keeping, payroll, etc. Their input to the forms is written to the database. others, maybe management, can query the database and generate reports. Since these forms are generic, I can't predict the database structure - other than to say that it will reflect HTML form fields and consist of a the data input from collection of edit boxes, memos, radio buttons and the like. Questions and remarks: A) how can I best structure the database, in terms of tables and columns? What about primary keys? My first thought was to use the control name to identify each column, then I realized that the user can edit the form and rename, so that maybe "name" becomes "employee" or "wages" becomes ":salary". I am leaning towards a unique number for each. B) how best to key the rows? I was thinking of a timestamp to allow me to query and a column for the row Id from A) C) I have to handle column rename/insert/delete. Foe deletion, I am unsure whether to delete the data from the database. Even if the user is not inputting it from the form any more he may wish to query what was previously entered. Or there may be some legal requirements to retain the data. Any gotchas in column rename/insert/delete? D) For the querying, I can have my PHP interrogate the database to get column names and generate a form with a list where each entry has a database column name, a checkbox to say if it should be used in the query and, based on column type, some selection criteria. That ought to be enough to build searches like "position = 'senior salesman' and salary 50k". E) I probably have to generate some fancy charts - graphs, histograms, pie charts, etc for query results of numerical data over time. I need to find some good FOSS PHP for this. F) What else have I forgotten? This all seems very tricky to me, but I am database n00b - maybe it is simple to you gurus?

  Read the article

• Stumbleupon type query...

  - by Chris Denman

  Wow, makes your head spin! I am about to start a project, and although my mySql is OK, I can't get my head around what required for this: I have a table of web addresses. id,url 1,http://www.url1.com 2,http://www.url2.com 3,http://www.url3.com 4,http://www.url4.com I have a table of users. id,name 1,fred bloggs 2,john bloggs 3,amy bloggs I have a table of categories. id,name 1,science 2,tech 3,adult 4,stackoverflow I have a table of categories the user likes as numerical ref relating to the category unique ref. For example: user,category 1,4 1,6 1,7 1,10 2,3 2,4 3,5 . . . I have a table of scores relating to each website address. When a user visits one of these sites and says they like it, it's stored like so: url_ref,category 4,2 4,3 4,6 4,2 4,3 5,2 5,3 . . . So based on the above data, URL 4 would score (in it's own right) as follows: 2=2 3=2 6=1 What I was hoping to do was pick out a random URL from over 2,000,000 records based on the current users interests. So if the logged in user likes categories 1,2,3 then I would like to ORDER BY a score generated based on their interest. If the logged in user likes categories 2 3 and 6 then the total score would be 5. However, if the current logged in user only like categories 2 and 6, the URL score would be 3. So the order by would be in context of the logged in users interests. Think of stumbleupon. I was thinking of using a set of VIEWS to help with sub queries. I'm guessing that all 2,000,000 records will need to be looked at and based on the id of the url it will look to see what scores it has based on each selected category of the current user. So we need to know the user ID and this gets passed into the query as a constant from the start. Ain't got a clue! Chris Denman

  Read the article

• Another C datatypes question

  - by b-gen-jack-o-neill

  Hello. Well, I completely get the most basic datatypes of C, like short, int, long, float, to be exact, all numerical types.These types are needed to be known perform right operations with right numbers. For example to use FPU to add two float numbers. So the compiler must know what the type is. But, when it comes to characters I am little bit off. I know that basic C datatype char is there for ASCII characters coding. But what I don´t know is, why you even need another datatype for characters. Why could not you just use 1 byte integer value to store ASCII character. If you call printf, you apecify the datatype in the call, so you could say to printf that the integer represents ASCII character. I dont know how cout resolves datatype, but I guess you could just specify it somehow. Another thing is, when you want to use Unicode, you must use datatype wchar. But, what if I would like to use some another, for example ISO, or Windows coding instead of UTF? Becouse wchar codes characters as UTF-16 or UTF-32 (I read its compiler specific). And, what if I would want to use for example some imaginary new 8 byte text coding? What datatype should I use for it? I am actually pretty confused of this, becouse I always expected that if I want to use UTF-32 instead of ASCII, I just tell compiler "get UTF-32 value of the character I typed and save it into 4 char field." I thought that text coding is to be dealt with by the end, print function for example. That I just need to specify the coding for the compiler to use, since Windows doesent use ASCII in win32 apps, I guess C compiler must convert the char I typed to ASCII from whatever the type is that windows sends to the C editor. And the last thing is, what if I want to use for example 25 Byte integer for some high math operations? C has no specify-yourself datatype. Yes, I know that this would be difficult since all the math operations would need to be changed, becouse CPU can not add 25 Bytes numbers together. But is there a way to do it? Or is there some math library for it? What if I want to compute Pi to 1000000000000000 digits? :) I know my question is pretty long, but I just wanted to explain my thoughts the best I can in English, since its not my native language it is difficult. And I believe there is simple answer to my question(s), something I missed that explains everything. I read lot about text coding, C tutorials, but nothing about his. Thank you for your time.

  Read the article

• Setting up a "to-many" relationship value dependency for a transient Core Data attribute

  - by Greg Combs

  I've got a relatively complicated Core Data relationship structure and I'm trying to figure out how to set up value dependencies (or observations) across various to-many relationships. Let me start out with some basic info. I've got a classroom with students, assignments, and grades (students X assignments). For simplicity's sake, we don't really have to focus much on the assignments yet. StudentObj <--->> ScoreObj <<---> AssignmentObj Each ScoreObj has a to-one relation with the StudentObj and the AssignmentObj. ScoreObj has real attributes for the numerical grade, the turnInDate, and notes. AssignmentObj.scores is the set of Score objects for that assignment (N = all students). AssignmentObj has real attributes for name, dueDate, curveFunction, gradeWeight, and maxPoints. StudentObj.scores is the set of Score objects for that student (N = all assignments). StudentObj also has real attributes like name, studentID, email, etc. StudentObj has a transient (calculated, not stored) attribute called gradeTotal. This last item, gradeTotal, is the real pickle. it calculates the student's overall semester grade using the scores (ScoreObj) from all their assignments, their associated assignment gradeWeights, curves, and maxPoints, and various other things. This gradeTotal value is displayed in a table column, along with all the students and their individual assignment grades. Determining the value of gradeTotal is a relatively expensive operation, particularly with a large class, therefore I want to run it only when necessary. For simplicity's sake, I'm not storing that gradeTotal value in the core data model. I don't mind caching it somewhere, but I'm having a bitch of a time determining where and how to best update that cache. I need to run that calculation for each student whenever any value changes that affects their gradeTotal. If this were a simple to-one relationship, I know I could use something like keyPathsForValuesAffectingGradeTotal ... but it's more like a many-to-one-to-many relationship. Does anyone know of an elegant (and KVC correct) solution? I guess I could tear through all those score and assignment objects and tell them to register their students as observers. But this seems like a blunt force approach.

  Read the article

• Are there known problems with >= and <= and the eval function in JS?

  - by Augier

  I am currently writing a JS rules engine which at one point needs to evaluate boolean expressions using the eval() function. Firstly I construct an equation as such: var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator + " " + "relation.value"; relation.relatedTrigger.previousValue is the value I want to compare. relation.operator is the operator (either "==", "!=", <=, "<", "", ="). relation.value is the value I want to compare with. I then simply pass this string to the eval function and it returns true or false as such: return eval(equation); This works absolutely fine (with words and numbers) or all of the operators except for = and <=. E.g. When evaluating the equation: relation.relatedTrigger.previousValue <= 100 It returns true when previousValue = 0,1,10,100 & all negative numbers but false for everything in between. I would greatly appreciate the help of anyone to either answer my question or to help me find an alternative solution. Regards, Augier. P.S. I don't need a speech on the insecurities of the eval() function. Any value given to relation.relatedTrigger.previousValue is predefined. edit: Here is the full function: function evaluateRelation(relation) { console.log("Evaluating relation") var currentValue; //if multiple values if(relation.value.indexOf(";") != -1) { var values = relation.value.split(";"); for (x in values) { var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator + " " + "values[x]"; currentValue = eval(equation); if (currentValue) return true; } return false; } //if single value else { //Evaluate the relation and get boolean var equation = "relation.relatedTrigger.previousValue" + " " + relation.operator + " " + "relation.value"; console.log("relation.relatedTrigger.previousValue " + relation.relatedTrigger.previousValue); console.log(equation); return eval(equation); } } Answer: Provided by KennyTM below. A string comparison doesn't work. Converting to a numerical was needed.

  Read the article

• jQuery - Sorting an array?

  - by Probocop

  Hi, I'm using Ajax to get some XML, and then filling in some fields on a form with the results. There is a numerical field on the form and I would like to sort the results by this number (highest first). How would I go about doing this in jQuery? My js function code is currently: function linkCounts() { ws_url = "http://archreport.epiphanydev2.co.uk/worker.php?query=linkcounts&domain="+$('#hidden_the_domain').val(); $.ajax({ type: "GET", url: ws_url, dataType: "xml", success: function(xmlIn){ results = xmlIn.getElementsByTagName("URL"); for ( var i = 0; i < results.length; i++ ) { $("#tb_domain_linkcount_url_"+(i+1)).val($(results[i].getElementsByTagName("Page")).text()); $("#tb_domain_linkcount_num_"+(i+1)).val($(results[i].getElementsByTagName("Links")).text()); } $('#img_linkcount_worked').attr("src","/images/worked.jpg"); }, error: function(){$('#img_linkcount_worked').attr("src","/images/failed.jpg");} }); } The Links tag is the one I'm wanting to sort it on. Thanks For reference the XML that's getting returned is like the following: <?xml version="1.0" encoding="utf-8" standalone="yes"?> <Response> <ResponseCode>1</ResponseCode> <ResponseStatus>OK</ResponseStatus> <ReportId>2</ReportId> <UrlChecked /> <MaxLinks>75</MaxLinks> <PagesFound>121</PagesFound> <URLs> <URL> <Page>http://www.epiphanysolutions.co.uk/blog</Page> <Links>78</Links> </URL> <URL> <Page>http://www.epiphanysolutions.co.uk/blog/</Page> <Links>78</Links> </URL> <URL> <Page>http://www.epiphanysolutions.co.uk/blog/author/daniel-peden/</Page> <Links>78</Links> </URL> <URL> <Page>http://www.epiphanysolutions.co.uk/blog/author/daniel-peden/page/2/</Page> <Links>78</Links> </URL> </URLS> </Response>

  Read the article

• Approaches for Content-based Item Recommendations

  - by PartlyCloudy

  Hello, I'm currently developing an application where I want to group similar items. Items (like videos) can be created by users and also their attributes can be altered or extended later (like new tags). Instead of relying on users' preferences as most collaborative filtering mechanisms do, I want to compare item similarity based on the items' attributes (like similar length, similar colors, similar set of tags, etc.). The computation is necessary for two main purposes: Suggesting x similar items for a given item and for clustering into groups of similar items. My application so far is follows an asynchronous design and I want to decouple this clustering component as far as possible. The creation of new items or the addition of new attributes for an existing item will be advertised by publishing events the component can then consume. Computations can be provided best-effort and "snapshotted", which means that I'm okay with the best result possible at a given point in time, although result quality will eventually increase. So I am now searching for appropriate algorithms to compute both similar items and clusters. At important constraint is scalability. Initially the application has to handle a few thousand items, but later million items might be possible as well. Of course, computations will then be executed on additional nodes, but the algorithm itself should scale. It would also be nice if the algorithm supports some kind of incremental mode on partial changes of the data. My initial thought of comparing each item with each other and storing the numerical similarity sounds a little bit crude. Also, it requires n*(n-1)/2 entries for storing all similarities and any change or new item will eventually cause n similarity computations. Thanks in advance! UPDATE tl;dr To clarify what I want, here is my targeted scenario: User generate entries (think of documents) User edit entry meta data (think of tags) And here is what my system should provide: List of similar entries to a given item as recommendation Clusters of similar entries Both calculations should be based on: The meta data/attributes of entries (i.e. usage of similar tags) Thus, the distance of two entries using appropriate metrics NOT based on user votings, preferences or actions (unlike collaborative filtering). Although users may create entries and change attributes, the computation should only take into account the items and their attributes, and not the users associated with (just like a system where only items and no users exist). Ideally, the algorithm should support: permanent changes of attributes of an entry incrementally compute similar entries/clusters on changes scale something better than a simple distance table, if possible (because of the O(n²) space complexity)

  Read the article

• Code Golf: Countdown Number Game

  - by Noldorin

  Challenge Here is the task, inspired by the well-known British TV game show Countdown. The challenge should be pretty clear even without any knowledge of the game, but feel free to ask for clarifications. And if you fancy seeing a clip of this game in action, check out this YouTube clip. It features the wonderful late Richard Whitely in 1997. You are given 6 numbers, chosen at random from the set {1, 2, 3, 4, 5, 6, 8, 9, 10, 25, 50, 75, 100}, and a random target number between 100 and 999. The aim is to make use the six given numbers and the four common arithmetic operations (addition, subtraction, multiplication, division; all over the rational numbers) to generate the target - or as close as possible either side. Each number may only be used once at most, while each arithmetic operator may be used any number of times (including zero.) Note that it does not matter how many numbers are used. Write a function that takes the target number and set of 6 numbers (can be represented as list/collection/array/sequence) and returns the solution in any standard numerical notation (e.g. infix, prefix, postfix). The function must always return the closest-possible result to the target, and must run in at most 1 minute on a standard PC. Note that in the case where more than one solution exists, any single solution is sufficient. Examples: {50, 100, 4, 2, 2, 4}, target 203 e.g. 100 * 2 + 2 + (4 / 4) e.g. (100 + 50) * 4 * 2 / (4 + 2) {25, 4, 9, 2, 3, 10}, target 465 e.g. (25 + 10 - 4) * (9 * 2 - 3) {9, 8, 10, 5, 9, 7), target 241 e.g. ((10 + 9) * 9 * 7) + 8) / 5 Rules Other than mentioned in the problem statement, there are no further restrictions. You may write the function in any standard language (standard I/O is not necessary). The aim as always is to solve the task with the smallest number of characters of code. Saying that, I may not simply accept the answer with the shortest code. I'll also be looking at elegance of the code and time complexity of the algorithm! My Solution I'm attempting an F# solution when I find the free time - will post it here when I have something! Format Please post all answers in the following format for the purpose of easy comparison: Language Number of characters: ??? Fully obfuscated function: (code here) Clear (ideally commented) function: (code here) Any notes on the algorithm/clever shortcuts it takes.

  Read the article

• Parallelism in .NET – Part 5, Partitioning of Work

  - by Reed

  When parallelizing any routine, we start by decomposing the problem.  Once the problem is understood, we need to break our work into separate tasks, so each task can be run on a different processing element.  This process is called partitioning. Partitioning our tasks is a challenging feat.  There are opposing forces at work here: too many partitions adds overhead, too few partitions leaves processors idle.  Trying to work the perfect balance between the two extremes is the goal for which we should aim.  Luckily, the Task Parallel Library automatically handles much of this process.  However, there are situations where the default partitioning may not be appropriate, and knowledge of our routines may allow us to guide the framework to making better decisions. First off, I’d like to say that this is a more advanced topic.  It is perfectly acceptable to use the parallel constructs in the framework without considering the partitioning taking place.  The default behavior in the Task Parallel Library is very well-behaved, even for unusual work loads, and should rarely be adjusted.  I have found few situations where the default partitioning behavior in the TPL is not as good or better than my own hand-written partitioning routines, and recommend using the defaults unless there is a strong, measured, and profiled reason to avoid using them.  However, understanding partitioning, and how the TPL partitions your data, helps in understanding the proper usage of the TPL. I indirectly mentioned partitioning while discussing aggregation.  Typically, our systems will have a limited number of Processing Elements (PE), which is the terminology used for hardware capable of processing a stream of instructions.  For example, in a standard Intel i7 system, there are four processor cores, each of which has two potential hardware threads due to Hyperthreading.  This gives us a total of 8 PEs – theoretically, we can have up to eight operations occurring concurrently within our system. In order to fully exploit this power, we need to partition our work into Tasks.  A task is a simple set of instructions that can be run on a PE.  Ideally, we want to have at least one task per PE in the system, since fewer tasks means that some of our processing power will be sitting idle.  A naive implementation would be to just take our data, and partition it with one element in our collection being treated as one task.  When we loop through our collection in parallel, using this approach, we’d just process one item at a time, then reuse that thread to process the next, etc.  There’s a flaw in this approach, however.  It will tend to be slower than necessary, often slower than processing the data serially. The problem is that there is overhead associated with each task.  When we take a simple foreach loop body and implement it using the TPL, we add overhead.  First, we change the body from a simple statement to a delegate, which must be invoked.  In order to invoke the delegate on a separate thread, the delegate gets added to the ThreadPool’s current work queue, and the ThreadPool must pull this off the queue, assign it to a free thread, then execute it.  If our collection had one million elements, the overhead of trying to spawn one million tasks would destroy our performance. The answer, here, is to partition our collection into groups, and have each group of elements treated as a single task.  By adding a partitioning step, we can break our total work into small enough tasks to keep our processors busy, but large enough tasks to avoid overburdening the ThreadPool.  There are two clear, opposing goals here: Always try to keep each processor working, but also try to keep the individual partitions as large as possible. When using Parallel.For, the partitioning is always handled automatically.  At first, partitioning here seems simple.  A naive implementation would merely split the total element count up by the number of PEs in the system, and assign a chunk of data to each processor.  Many hand-written partitioning schemes work in this exactly manner.  This perfectly balanced, static partitioning scheme works very well if the amount of work is constant for each element.  However, this is rarely the case.  Often, the length of time required to process an element grows as we progress through the collection, especially if we’re doing numerical computations.  In this case, the first PEs will finish early, and sit idle waiting on the last chunks to finish.  Sometimes, work can decrease as we progress, since previous computations may be used to speed up later computations.  In this situation, the first chunks will be working far longer than the last chunks.  In order to balance the workload, many implementations create many small chunks, and reuse threads.  This adds overhead, but does provide better load balancing, which in turn improves performance. The Task Parallel Library handles this more elaborately.  Chunks are determined at runtime, and start small.  They grow slowly over time, getting larger and larger.  This tends to lead to a near optimum load balancing, even in odd cases such as increasing or decreasing workloads.  Parallel.ForEach is a bit more complicated, however. When working with a generic IEnumerable<T>, the number of items required for processing is not known in advance, and must be discovered at runtime.  In addition, since we don’t have direct access to each element, the scheduler must enumerate the collection to process it.  Since IEnumerable<T> is not thread safe, it must lock on elements as it enumerates, create temporary collections for each chunk to process, and schedule this out.  By default, it uses a partitioning method similar to the one described above.  We can see this directly by looking at the Visual Partitioning sample shipped by the Task Parallel Library team, and available as part of the Samples for Parallel Programming.  When we run the sample, with four cores and the default, Load Balancing partitioning scheme, we see this: The colored bands represent each processing core.  You can see that, when we started (at the top), we begin with very small bands of color.  As the routine progresses through the Parallel.ForEach, the chunks get larger and larger (seen by larger and larger stripes). Most of the time, this is fantastic behavior, and most likely will out perform any custom written partitioning.  However, if your routine is not scaling well, it may be due to a failure in the default partitioning to handle your specific case.  With prior knowledge about your work, it may be possible to partition data more meaningfully than the default Partitioner. There is the option to use an overload of Parallel.ForEach which takes a Partitioner<T> instance.  The Partitioner<T> class is an abstract class which allows for both static and dynamic partitioning.  By overriding Partitioner<T>.SupportsDynamicPartitions, you can specify whether a dynamic approach is available.  If not, your custom Partitioner<T> subclass would override GetPartitions(int), which returns a list of IEnumerator<T> instances.  These are then used by the Parallel class to split work up amongst processors.  When dynamic partitioning is available, GetDynamicPartitions() is used, which returns an IEnumerable<T> for each partition.  If you do decide to implement your own Partitioner<T>, keep in mind the goals and tradeoffs of different partitioning strategies, and design appropriately. The Samples for Parallel Programming project includes a ChunkPartitioner class in the ParallelExtensionsExtras project.  This provides example code for implementing your own, custom allocation strategies, including a static allocator of a given chunk size.  Although implementing your own Partitioner<T> is possible, as I mentioned above, this is rarely required or useful in practice.  The default behavior of the TPL is very good, often better than any hand written partitioning strategy.

  Read the article

< Previous Page | 18 19 20 21 22 23 24  | Next Page >