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  • Sliding Response after a Point-Square Collision

    - by mars
    In general terms and pseudo-code, what would be the best way to have a collision response of sliding along a wall if the wall is actually just a part of an entire square that a point is colliding into? The collision test method used is a test to see if the point lies in the square. Should I divide the square into four lines and just calculate the shortest distance to the line and then move the point back that distance?If so, then how can I determine which edge of the square the point is closest to after collision?

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  • Rewriting a for loop in pure NumPy to decrease execution time

    - by Statto
    I recently asked about trying to optimise a Python loop for a scientific application, and received an excellent, smart way of recoding it within NumPy which reduced execution time by a factor of around 100 for me! However, calculation of the B value is actually nested within a few other loops, because it is evaluated at a regular grid of positions. Is there a similarly smart NumPy rewrite to shave time off this procedure? I suspect the performance gain for this part would be less marked, and the disadvantages would presumably be that it would not be possible to report back to the user on the progress of the calculation, that the results could not be written to the output file until the end of the calculation, and possibly that doing this in one enormous step would have memory implications? Is it possible to circumvent any of these? import numpy as np import time def reshape_vector(v): b = np.empty((3,1)) for i in range(3): b[i][0] = v[i] return b def unit_vectors(r): return r / np.sqrt((r*r).sum(0)) def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) A = 1e-7 num = A*(3*np.sum(mom_i*r_unit, 0)*r_unit - mom_i) den = np.sqrt(np.sum(relative*relative, 0))**3 B = np.sum(num/den, 1) return B N = 20000 # number of dipoles r_i = np.random.random((3,N)) # positions of dipoles mom_i = np.random.random((3,N)) # moments of dipoles a = np.random.random((3,3)) # three basis vectors for this crystal n = [10,10,10] # points at which to evaluate sum gamma_mu = 135.5 # a constant t_start = time.clock() for i in range(n[0]): r_frac_x = np.float(i)/np.float(n[0]) r_test_x = r_frac_x * a[0] for j in range(n[1]): r_frac_y = np.float(j)/np.float(n[1]) r_test_y = r_frac_y * a[1] for k in range(n[2]): r_frac_z = np.float(k)/np.float(n[2]) r_test = r_test_x +r_test_y + r_frac_z * a[2] r_test_fast = reshape_vector(r_test) B = calculate_dipole(r_test_fast, r_i, mom_i) omega = gamma_mu*np.sqrt(np.dot(B,B)) # write r_test, B and omega to a file frac_done = np.float(i+1)/(n[0]+1) t_elapsed = (time.clock()-t_start) t_remain = (1-frac_done)*t_elapsed/frac_done print frac_done*100,'% done in',t_elapsed/60.,'minutes...approximately',t_remain/60.,'minutes remaining'

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  • Calculate angle of moving ball after collision with angled or sloped wall that is a 2D line segment

    - by Ben Mc
    If you have a "ball" inside a 2D polygon, made up of say, 4 line segments that act as bounding walls, how do you calculate the angle of the ball after the collision with the irregularly sloped wall? I know how to make the ball bounce if the wall is horizontal, vertical, or at a 45 degree angle. I also have my code setup to detect a collision with the wall. I've read about dot products and normals, but I cannot figure out how to implement these in Java / Android. I'm completely stumped and feel like I've looked up everything 10 pages deep in Google 10 times now. I'm burned out trying to figure this out, I hope someone can help.

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  • Calculating collision for a moving circle, without overlapping the boundaries

    - by Robert Vella
    Let's say I have circle bouncing around inside a rectangular area. At some point this circle will collide with one of the surfaces of the rectangle and reflect back. The usual way I'd do this would be to let the circle overlap that boundary and then reflect the velocity vector. The fact that the circle actually overlaps the boundary isn't usually a problem, nor really noticeable at low velocity. At high velocity it becomes quite clear that the circle is doing something it shouldn't. What I'd like to do is to programmatically take reflection into account and place the circle at it's proper position before displaying it on the screen. This means that I have to calculate the point where it hits the boundary between it's current position and it's future position -- rather than calculating it's new position and then checking if it has hit the boundary. This is a little bit more complicated than the usual circle/rectangle collision problem. I have a vague idea of how I should do it -- basically create a bounding rectangle between the current position and the new position, which brings up a slew of problems of it's own (Since the rectangle is rotated according to the direction of the circle's velocity). However, I'm thinking that this is a common problem, and that a common solution already exists. Is there a common solution to this kind of problem? Perhaps some basic theories which I should look into?

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  • How to get points that intersect the treadline?

    - by chutsu
    Basically I did the Cavendish experiment, and I have a damped sinusoidal wave plotted on Excel. With Position (mm) against Time (s). My problem is that I have added a tread line through the wave function, and wish to calculate the points of which the wave function intersects the tread line. From this I will then be able to calculate the time period. At the moment I'm just having difficulty getting the intersects.. Thanks

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  • How to get colliding effect or bouncy when ball hits the track.

    - by Chandan Shetty SP
    I am using below formula to move the ball circular, where accelX and accelY are the values from accelerometer, it is working fine. But the problem in this code is mRadius (I fixed its value to 50), i need to change mRadius according to accelerometer values and also i need bouncing effect when it touches the track. Currently i am developing code by assuming only one ball is on the board. float degrees = -atan2(accelX, accelY) * 180 / 3.14159; int x = cCentrePoint.x + mRadius * cos(degreesToRadians(degrees)); int y = cCentrePoint.y + mRadius * sin(degreesToRadians(degrees)); Here is the snap of the game i want to develop: Updated: I am sending the updated code... mRadius = 5; mRange = NSMakeRange(0,60); -(void) updateBall: (UIAccelerationValue) accelX withY:(UIAccelerationValue)accelY { float degrees = -atan2(accelX, accelY) * 180 / 3.14159; int x = cCentrePoint.x + mRadius * cos(degreesToRadians(degrees)); int y = cCentrePoint.y + mRadius * sin(degreesToRadians(degrees)); //self.targetRect is rect of ball Object self.targetRect = CGRectMake(newX, newY, 8, 9); self.currentRect = self.targetRect; //http://books.google.co.in/books?id=WV9glgdrrrUC&pg=PA455#v=onepage&q=&f=false static NSDate *lastDrawTime; if(lastDrawTime!=nil) { NSTimeInterval secondsSinceLastDraw = -([lastDrawTime timeIntervalSinceNow]); ballXVelocity = ballXVelocity + (accelX * secondsSinceLastDraw) * [self isTouchedTrack:mRadius andRange:mRange]; ballYVelocity = ballYVelocity + -(accelY * secondsSinceLastDraw) * [self isTouchedTrack:mRadius andRange:mRange]; distXTravelled = distXTravelled + secondsSinceLastDraw * ballXVelocity * 50; distYTravelled = distYTravelled + secondsSinceLastDraw * ballYVelocity * 50; CGRect temp = self.targetRect; temp.origin.x += distXTravelled; temp.origin.y += distYTravelled; int radius = (temp.origin.x - cCentrePoint.x) / cos(degreesToRadians(degrees)); if( !NSLocationInRange(abs(radius),mRange)) { //Colided with the tracks...Need a better logic here ballXVelocity = -ballXVelocity; } else { // Need a better logic here self.targetRect = temp; } //NSLog(@"angle = %f",degrees); } [lastDrawTime release]; lastDrawTime = [ [NSDate alloc] init]; } In the above code i have initialized mRadius and mRange(indicate track) to some constant for testing, i am not getting the moving of the ball as i expected( bouncing effect when Collided with track ) with respect to accelerometer. Help me to recognize where i went wrong or send some code snippets or links which does the similar job. I am searching for better logic than my code, if you found share with me.

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  • Determining if and where a photon will collide with a polygon in 3D space.

    - by Peter
    The problem is straight forward: 1) We have a photon traveling from Point 1 (x,y,z) to Point 2 (x,y,z), both of which could be located anywhere in 3D space. 2) We have a polygon that is both rotated randomly on the x-axis and/or y-axis and also located anywhere in 3D space. 3) We want to find: a) if the photon will collide with the polygon at all and b) if it does where will that be (x,y,z)? An image of the problem: http://dl.dropbox.com/u/3150177/Programming/3D/Math/Photon%20Path/Photon%20Path.png The aim of this is to calculate how the photon's path should be altered from an interaction(s) with the polygon(s). I am reading up on this subject now but I was wondering if anyone could give me a head start. Thanks in advance.

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  • Vacuum spread in a tile-based space game (like in Faster Than Light game)

    - by Reeze
    I've a space game with tilemap that looks like this (simplified): Map view - from top (like in SimCity 1) 0 - room space, 1 - some kind of wall, 8 - "lock" beetween rooms public int[,] _layer = new int[,] { { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 1, 1, 8, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 1, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 1, 0, 8, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, }; Each tile contains Air property (100 = air, 0 = vacuum). I made a little helper method to take tiles near tile with vacuum (to "suck air"): Point[] GetNearCells(Point cell, int distance = 1, bool diag = false) { Point topCell = new Point(cell.X, cell.Y - distance); Point botCell = new Point(cell.X, cell.Y + distance); Point leftCell = new Point(cell.X - distance, cell.Y); Point rightCell = new Point(cell.X + distance, cell.Y); if (diag) { return new[] { topCell, botCell, leftCell, rightCell }; } Point topLeftCell = new Point(cell.X - distance, cell.Y - distance); Point topRightCell = new Point(cell.X + distance, cell.Y + distance); Point botLeftCell = new Point(cell.X - distance, cell.Y - distance); Point botRightCell = new Point(cell.X - distance, cell.Y - distance); return new[] { topCell, botCell, leftCell, rightCell, topLeftCell, topRightCell, botLeftCell, botRightCell }; } What is the best practice to fill rooms with vacuum (decrease air) from some point? Should i use some kind of water flow? Thank you for any help!

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  • how to avoid clutch billiard balls?

    - by Nait87
    I'm working on the simple behaviour of billiard balls in a collision with each other. All works normal, but there was a problem when facing a few easy balls is the effect of coupling balls and they're cool with each other. Tell me how to prevent this. bool MGBilliard::CollisingBall(CCPoint curr_point, CCPoint next_point) { float dx = next_point.x - (curr_point.x + dvdt.x); float dy = next_point.y - (curr_point.y - dvdt.y); float d = dx*dx+dy*dy; return d <= BALL_RADIUS * BALL_RADIUS; } double MGBilliard::angleCollisionBalls(Ball* current, Ball* next) { double na; double dx = fabs(next->location.x - current->location.x); double dy = fabs(next->location.y - current->location.y); na = atan(fabs(dy/dx)); if(atan(fabs(current->location.y/current->location.x)) < atan(fabs(next->location.y/next->location.x))) na = current->angle - na; else if(atan(fabs(current->location.y/current->location.x)) > atan(fabs(next->location.y/next->location.x))) na = current->angle + na; return na; } for(unsigned int i = 0;i<BALL_COUNT;++i) { if(vBalls[i]->speed > 0){ vBalls[i]->speed += vBalls[i]->acceleration; float dsdt = vBalls[i]->speed*dt; dvdt.x = dsdt*cos(vBalls[i]->angle); dvdt.y = dsdt*sin(vBalls[i]->angle); vBalls[i]->location.x += dvdt.x; vBalls[i]->location.y += dvdt.y; for(unsigned int j = 1; j < BALL_COUNT; ++j) { if(i == j) continue; if(CollisingBall(vBalls[i]->spriteBall->getPosition(),vBalls[j]->spriteBall->getPosition())) { vBalls[j]->speed = 600; double angle; angle = angleCollisionBalls(vBalls[i],vBalls[j]); vBalls[i]->angle = (float)-angle; vBalls[j]->angle = (float)angle; } } } }

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  • Bouncing a ball off a surface

    - by Sagekilla
    Hi all, I'm currently in the middle of writing a game like Breakout, and I was wondering how I could properly bounce a ball off a surface. I went with the naive way of rotating the velocity by 180 degrees, which was: [vx, vy] -> [-vy, vx] Which (unsurprisingly) didn't work so well. If I know the position and veocity of the ball, as well as the point the ball would hit (but is going to instead bounce off of) how can I bounce it off that point? I don't need any language specific code. If anyone could provide a small, mathematical formula on how to properly do this that would work fine for me. I also need this to work with integer positions and velocity (I can't use floating point anywhere). Thanks!

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  • Level designing with Cocos2d and Box2d

    - by Majster
    I want to learn how to make levels using cocos2d and box2d (for iOS). I am talking about a 2d platformer such as Limbo or Braid or something like that. How can I design and build levels like this? I have seen Level Helper for cocos2d but its not free and I don't think it makes physic objects for box2d. How is this accomplished in real games? How to make camera move with character and so on. Any starting points would be much appreciated.

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  • What technologies to use for a particle system with enormous calculation demand?

    - by Amir Rezaei
    I have a particle system with X particles. Each particle tests for collision with other particles. This gives X*X = X^2 collision tests per frame. For 60f/s, this corresponds to 60*X^2 collision detection per second. What is the best technological approach for these intensive calculations? Should I use F#, C, C++ or C#, or something else? The following are constraints The code is written in C# with the latest XNA Multi-threaded may be considered No special algorithm that tests the collision with the nearest neighbors or that reduces the problem The last constraint may be strange, so let me explain. Regardless constraint 3, given a problem with enormous computational requirement what would be the best approach to solve the problem. An algorithm reduces the problem; still the same algorithm may behave different depending on technology. Consider pros and cons of CLR vs native C.

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  • Calculating collission for a moving circle, without overlapping the boundaries

    - by Robert Vella
    Let's say I have circle bouncing around inside a rectangular area. At some point this circle will collide with one of the surfaces of the rectangle and reflect back. The usual way I'd do this would be to let the circle overlap that boundary and then reflect the velocity vector. The fact that the circle actually overlaps the boundary isn't usually a problem, nor really noticeable at low velocity. At high velocity it becomes quite clear that the circle is doing something it shouldn't. What I'd like to do is to programmitically take reflection into account and place the circle at it's proper position before displaying it on the screen. This means that I have to calculate the point where it hits the boundary between it's current position and it's future position -- rather than calculating it's new position and then checking if it has hit the boundary. This is a little bit more complicated than the usual circle/rectangle collission problem. I have a vague idea of how I should do it -- basically create a bounding rectangle between the current position and the new position, which brings up a slew of problems of it's own (Since the rectangle is rotated according to the direction of the circle's velocity). However, I'm thinking that this is a common problem, and that a common solution already exists. Is there a common solution to this kind of problem? Perhaps some basic theories which I should look into?

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  • Collision Handling in Javascript - Particles Get Stuck

    - by Conner Ruhl
    I am trying to recreate this, and I have been fairly successful. I am having issues with the collision handling though. Although the collision handling seems to work, it has very strange behavior. Here is what I have so far. This is the code that handles collisions: var dx = particle2.getX() - particle1.getX(); var dy = particle2.getY() - particle1.getY(); var angle = Math.atan2(dy, dx); var newP2X = particle1.getX() + (particle1.getRadius() + particle2.getRadius()) * Math.cos(angle); var newP2Y = particle1.getY() + (particle1.getRadius() + particle2.getRadius()) * Math.sin(angle); particle2.setX(newP2X); particle2.setY(newP2Y); var p1Vxi = particle1.getVx(); var p1Vyi = particle1.getVy(); var p1Mass = particle1.getMass(); var p2Vxi = particle2.getVx(); var p2Vyi = particle2.getVy(); var p2Mass = particle2.getMass(); var vxf = (p1Mass * p1Vxi + p2Mass * p2Vxi) / (p1Mass + p2Mass); var vyf = (p1Mass * p1Vyi + p2Mass * p2Vyi) / (p1Mass + p2Mass); particle1.setVx(vxf); particle1.setVy(vyf); particle2.setVx(vxf); particle2.setVy(vyf); EDIT: I have tried to change it to inelastic collisions like suggested, but for some reason the balls collide erratically. Check it out here. Any help is much appreciated!

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  • How to calculate deceleration rate of a flipping coin (in c)?

    - by Horace Ho
    A flipping coin on table will slow down and drop to the table surface, facing up or down. How can I calculate the flip-per-second declaration rate over time? For example, assuming the coin is at 10 flipping per second when it starts how long will it take to stop? For each second (9, 8, 7, 6 ... 3, 2, 1, stop), how is the flipping rate changed? Friction can be approximated as some real world objects (say, a metallic coin on a wooden table). Thanks!

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  • Finding vectors with two points

    - by Christian Careaga
    We're are trying to get the direction of a projectile but we can't find out how For example: [1,1] will go SE [1,-1] will go NE [-1,-1] will go NW and [-1,1] will go SW we need an equation of some sort that will take the player pos and the mouse pos and find which direction the projectile needs to go. Here is where we are plugging in the vectors: def update(self): self.rect.x += self.vector[0] self.rect.y += self.vector[1] Then we are blitting the projectile at the rects coords.

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  • How to calculate shot angle and velocity to hit a moving target?

    - by Guen
    I am developing a 2D Android game and I am making an aiming algorithm for AI projectiles to hit enemies either following a path, or free moving. At the moment it just calculates where the target will be after a distance and fires a projectile to meet it at that distance. Of course this means varying the projectile speed to meet the target. Does anyone have any tips for a simple-ish algorithm (optimal-ish) to calculate when the projectile needs to fire and where it needs to aim if it can only travel at a constant velocity? Say the projectile goes twice the speed of the target? The only way I can think of involves searching and seems quite large.

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  • How would I make a mouse controlled physics object in Box2D / AS3?

    - by Marty Wallace
    I recently created this tennis game using my own basic physics: http://martywallace.com/sandbox/tennis/ Basically a tennis racquet sticks to your mouse and you can hit the tennis balls upward. The physics aren't that great, and I want to make a more interesting version of this game with milestones and levels in Flash. I am planning to use Box2D because I have moderate experience with it. I'm not sure how to go about creating the racquet - as far as I understand Box2D, the racquet needs a velocity to influence the velocities of the balls when you hit them (so that you can hit them harder or softer upward to keep them up). With that said, I'm assuming I can't just have a kinematic body that will have its position set to the mouse, because it won't affect the velocities of the balls as expected. I've also thought about setting the velocity to the difference between the racquet position and the mouse each frame, but I am concerned that won't provide accurate positioning and am also thinking that the velocity could end up really large if you move the mouse quickly. What is the correct way to have a physics object locked to the mouse but also to have its displacement in the last frame (from where it was to the mouse) affect the balls?

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  • Sprite Kit - containsPoint for SKPhysicsBody?

    - by gj15987
    I have a ball bouncing around the screen. I can pick it up and drag it onto a "bucket". When my touches finish, I use the containsPoint function to check and see if I have dropped the ball onto the bucket. This works fine, however, I actually want to check whether the ball is dropped onto the bucket node's physics body because my "bucket" is actually just an oval, and so I've applied a physics body which is the same shape as the oval, so that the white space around the oval isn't included in the physics simulation. I can't seem to find a "containsPoint" function for physics bodies. Can anyone advise on how I'd check for this? To summarise, I want to drop a node, onto a specific part of another node (or its physics body) and trigger an event. Thanks in advance.

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  • When to detect collisions in game loop

    - by Ciaran
    My game loop uses a fixed time step to do "physics" updates, say every 20 ms. In here I move objects. I draw frames as frequently as possible. I work out a value between 0 and 1 to represent the proportion of the physics tick that is complete and interpolate between the previous and current physics state before drawing. It results in a smoother game assuming the frame rate is higher than the physics update rate. I am currently doing the collision detection in the physics update routine. I was wondering should it instead take place in the interpolated draw routine where the positions match what the user sees? Collisions can result in explosions by the way.

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  • Need efficient way to keep enemy from getting hit multiple times by same source

    - by TenFour04
    My game's a simple 2D one, but this probably applies to many types of scenarios. Suppose my player has a sword, or a gun that shoots a projectile that can pass through and hit multiple enemies. While the sword is swinging, there is a duration where I am checking for the sword making contact with any enemy on every frame. But once an enemy is hit by that sword, I don't want him to continue getting hit over and over as the sword follows through. (I do want the sword to continue checking whether it is hitting other enemies.) I've thought of a couple different approaches (below), but they don't seem like good ones to me. I'm looking for a way that doesn't force cross-referencing (I don't want the enemy to have to send a message back to the sword/projectile). And I'd like to avoid generating/resetting multiple array lists with every attack. Each time the sword swings it generates a unique id (maybe by just incrementing a global static long). Every enemy keeps a list of id's of swipes or projectiles that have already hit them, so the enemy knows not to get hurt by something multiple times. Downside is that every enemy may have a big list to compare to. So projectiles and sword swipes would have to broadcast their end-of-life to all enemies and cause a search and remove on every enemy's array list. Seems kind of slow. Each sword swipe or projectile keeps its own list of enemies that it has already hit so it knows not to apply damage. Downsides: Have to generate a new list (probably pull from a pool and clear one) every time a sword is swung or a projectile shot. Also, this breaks down modularity, because now the sword has to send a message to the enemy, and the enemy has to send a message back to the sword. Seems to me that two-way streets like this are a great way to create very difficult-to-find bugs.

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