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  • XNA Track rotated pixel positions

    - by jonny adams
    Hi, Im making a game in xna where a tank has to move over a landscape. I need to be able find the bottom of the tank when it is rotated so I can make it move up and down as the player goes over the landscape. for example if i have a sprite at with its top left corner at 400,300 and i rotate it around its center by 45 degrees around its center, how do i find the new locations of the bottom track. Thanks

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  • Implementing a hilbert map of the internet

    - by Martin
    In the XKCD comic 195 a design for a map of the internet address space is suggested using a hilbert curve so that items from a similar IPs will be clustered together. Given an IP address, how would I calculate the 2D coordinates (in the range zero to one) that this IP is located on such a map?

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  • simplify expression k/m%n

    - by aaa
    hello. Simple question, is it possible to simplify (or replace division or modulo by less-expensive operation) (k/m)%n where variables are integers and operators are C style division and modulo operators. what about the case where m and n are constants (both or just one), not based 2? Thank you

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  • Can someone explain how this works?

    - by Dan Howard
    Key in the first three digits of your phone number (NOT the Area code...) Multiply by 80 Add 1 Multiply by 250 Add to this the last 4 digits of your phone number Add to this the last 4 digits of your phone number again. Subtract 250 Divide number by 2 Do you recognize the answer??

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  • Arbitrary-precision arithmetic Explanation

    - by TT
    I'm trying to learn C and have come across the inability to work with REALLY big numbers (i.e., 100 digits, 1000 digits, etc.). I am aware that there exist libraries to do this, but I want to attempt to implement it myself. I just want to know if anyone has or can provide a very detailed, dumbed down explanation of arbitrary-precision arithmetic. Thanks!

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  • How do i know if this is random enough?

    - by David
    I wrote a program in java that rolls a die and records the total number of times each value 1-6 is rolled. I rolled 6 Million times. Here's the distribution: #of 0's: 0 #of 1's: 1000068 #of 2's: 999375 #of 3's: 999525 #of 4's: 1001486 #of 5's: 1000059 #of 6's: 999487 (0 wasn't an option.) Is this distribution consistant with random dice rolls? What objective statistical tests might confirm that the dice rolls are indeed random enough?

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  • How to write an intersects for Shapes in android

    - by Rafael T
    I have an written an Object called Shape which has a Point representing the topLeftCorner and a Dimension with represents its width and height. To get the topRightCorner I can simply add the width to the topLeftPoint.x. I use to rotate them on a certain degree around their center. The problem after the rotation is, that my intersects(Shape) method fails, because it does not honor the rotation of the Shapes. The rotation will be the same for each Shape. My current implementation looks like this inside my Shape Object: public boolean intersects(Shape s){ // functions returning a Point of shape s return intersects(s.topLeft()) || intersects(s.topRight()) || intersects(s.bottomLeft()) || intersects(s.bottomRight()) || intersects(s.leftCenter()) || intersects(s.rightCenter()) || intersects(s.center()); } public boolean intersects(Point p){ return p.x >= leftX() && p.x <= rightX() && p.y >= topY() && p.y <= bottomY(); } Basically I need functions like rotatedLeftX() or rotatedTopRight() to work properly. Also for that calculation I think it doesn't matter when the topLeft point before a rotation of ie 90 will turn into topRight... I already read this and this Question here, but do not understand it fully.

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  • Function to get X, Y position of an object orbiting a point, given a distance and angle in radians?

    - by Jake Petroules
    I am trying to code a function for a camera that orbits a point. Assume a 3d coordinate plane where Z is up. Ignore Z. Let's say the camera's position starts at (0, 0, z). The object to orbit is at, say (50, 50, z). So we have a distance of ~70 units. Calling the function with {(50, 50, z), 70, x} where x is the position in orbit, in radians, should return where the position of the camera should be. I believe this involves cos and tan but my trig isn't that great... point3d getCameraPosition(point3d objectPosition, float distance, float rotationRadians) { // ??? }

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  • Is OOP based on any branch of mathematics?

    - by ektrules
    I know relational databases are based on set-theory, functional programming is based on lambda calculus, logic programming is based on logic (of course :)), and now that I think of it; I'm not sure if imperative and generic programming is based on any particular branch of mathematics either.

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  • How can I evaluate the connectedness of my nodes?

    - by Travis Leleu
    I've got a space that has nodes that are all interconnected, based on a "similarity score". I would like to determine how "connected" a node is with the others. My purpose is to find nodes that are poorly connected to make sure that the backlink from the other node is prioritized. Perhaps an example would help. I've got a web page that links to my other pages based on a similarity score. Suppose I have the pages: A, B, C, ... A has a backlink from every other page, so it's very well connected. It also has links to all my other pages (each line in the graph is essentially bidirectional). B only has 1 backlink, from A. C has a link from A and D. I would like to make sure that the A-B link is prioritized over the A-C link (even if the similarity score between C and A is higher than B and A). In short, I would like to evaluate which nodes are least and best connected, so that I can mangle the results to my means. I believe this is Graph Connectedness, but I'm at a loss to develop a (simple) algorithm that will help me here. Simply counting the backlinks to a node may be a starting point -- but then how do I take the next step, which is to properly weight the links on the original node (A, in the example above)?

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  • Facebook Hacker Cup: Power Overwhelming

    - by marcog
    A lot of people at Facebook like to play Starcraft II™. Some of them have made a custom game using the Starcraft II™ map editor. In this game, you play as the noble Protoss defending your adopted homeworld of Shakuras from a massive Zerg army. You must do as much damage to the Zerg as possible before getting overwhelmed. You can only build two types of units, shield generators and warriors. Shield generators do no damage, but your army survives for one second per shield generator that you build. Warriors do one damage every second. Your army is instantly overrun after your shield generators expire. How many shield generators and how many warriors should you build to inflict the maximum amount of damage on the Zerg before your army is overrun? Because the Protoss value bravery, if there is more than one solution you should return the one that uses the most warriors. Constraints 1 = G (cost for one shield generator) = 100 1 = W (cost for one warrior) = 100 G + W = M (available funds) = 1000000000000 (1012)

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  • How are a session identifiers generated?

    - by Asaf R
    Most web applications depend on some kind of session with the user (for instance, to retain login status). The session id is kept as a cookie in the user's browser and sent with every request. To make it hard to guess the next user's session these session-ids need to be sparse and somewhat random. The also have to be unique. The question is - how to efficiently generate session ids that are sparse and unique? This question has a good answer for unique random numbers, but it seems not scalable for a large range of numbers, simply because the array will end up taking a lot of memory.

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  • Efficiency of manually written loops vs operator overloads (C++)

    - by Sagekilla
    Hi all, in the program I'm working on I have 3-element arrays, which I use as mathematical vectors for all intents and purposes. Through the course of writing my code, I was tempted to just roll my own Vector class with simple +, -, *, /, etc overloads so I can simplify statements like: for (int i = 0; i < 3; i++) r[i] = r1[i] - r2[i]; // becomes: r = r1 - r2; Which should be more or less identical in generated code. But when it comes to more complicated things, could this really impact my performance heavily? One example that I have in my code is this: Manually written version: for (int j = 0; j < 3; j++) { p.vel[j] = p.oldVel[j] + (p.oldAcc[j] + p.acc[j]) * dt2 + (p.oldJerk[j] - p.jerk[j]) * dt12; p.pos[j] = p.oldPos[j] + (p.oldVel[j] + p.vel[j]) * dt2 + (p.oldAcc[j] - p.acc[j]) * dt12; } Using a Vector class with operator overloads: p.vel = p.oldVel + (p.oldAcc + p.acc) * dt2 + (p.oldJerk - p.jerk) * dt12; p.pos = p.oldPos + (p.oldVel + p.vel) * dt2 + (p.oldAcc - p.acc) * dt12; I am compiling my code for maximum possible speed, as it's extremely important that this code runs quickly and calculates accurately. So will me relying on my Vector's for these sorts of things really affect me? For those curious, this is part of some numerical integration code which is not trivial to run in my program. Any insight would be appreciated, as would any idioms or tricks I'm unaware of.

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  • PHP given a series of arbitrary numbers, how can I choose a logical max value on a line graph?

    - by stormist
    I am constructing a line graph in PHP. I was setting the max value of the line graph to the max value of my collection of items, but this ended up making the graph less readable you are unable to view the highest line on the graph as it intersects with the top of it. So what I need is basically a formula to take a set of numbers and calculate what the logical max value of on the line graph should be.. so some examples 3500 250 10049 45394 434 312 Max value on line graph should probably be 50000 493 412 194 783 457 344 max value on line graph would ideally be 1000 545 649 6854 5485 11545 In this case, 12000 makes sense as max value So something as simple as rounding upward to the nearest thousandth might work but I'd need it to progressively increase as the numbers got bigger. (50000 instead of 46,000 in first example) The maximum these numbers will ever be is about a million. Any recommendations would be greatly appreciated, thank you.

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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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  • Interpolating height for a point inside a grid based on a discrete height function.

    - by fastrack20
    Hi, I have been wracking my brain to come up with a solution to this problem. I have a lookup table that returns height values for various points (x,z) on the grid. For instance I can calculate the height at A, B, C and D in Figure 1. However, I am looking for a way to interpolate the height at P (which has a known (x,z)). The lookup table only has values at the grid intervals, and P lies between these intervals. I am trying to calculate values s and t such that: A'(s) = A + s(C-A) B'(t) = B + t(P-B) I would then use the these two equations to find the intersection point of B'(t) with A'(s) to find a point X on the line A-C. With this I can calculate the height at this point X and with that the height at point P. My issue lies in calculating the values for s and t. Any help would be greatly appreciated.

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  • How to generate correlated binary variables

    - by jonalm
    Dear All I need to generate a series of N random binary variables with a given correlation function. Let x = {x_i} be a series of binary variables (taking the value 0 or 1, i running form 1 to N). The marginal probability is given Pr(x_i = 1) = p, and the values should be correlated in the following way E[ x_i x_j ] = const * |i-j|^-alfa where alfa is a positive number. Is it possible to generate a series like this? preferably in python.

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  • Least common multiple for 3 or more numbers

    - by paan
    How do you calculate the least common multiple of multiple numbers? So far I've only been able to calculate it between two numbers. But have no idea how to expand it to calculate 3 or more numbers. So far this is how I did it LCM = num1 * num2 / gcd ( num1 , num2 ) With gcd is the function to calculate the greatest common divisor for the numbers. Using euclidean algorithm But I can't figure out how to calculate it for 3 or more numbers.

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