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  • Help to translate SQL query to Relational Algebra

    - by Mestika
    Hi everyone, I'm having some difficulties with translating some queries to Relational Algebra. I've a great book about Database Design and here is a chapter about Relational Algebra but I still seem to have some trouble creating the right one: Thoes queries I've most difficuelt with is these: SELECT COUNT( cs.student_id ) AS counter FROM course c, course_student cs WHERE c.id = cs.course_id AND c.course_name = 'Introduction to Database Design' SELECT COUNT( cs.student_id ) FROM Course c INNER JOIN course_student cs ON c.id = cs.course_id WHERE c.course_name = 'Introduction to Database Design' and SELECT COUNT( * ) FROM student JOIN grade ON student.f_name = "Andreas" AND student.l_name = "Pedersen" AND student.id = grade.student_id I know the notation can be a bit hard to paste into HTML forum, but maybe just use some common name or the Greek name. Thanks in advance Mestika

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  • Haskell Linear Algebra Matrix Library for Arbitrary Element Types

    - by Johannes Weiß
    I'm looking for a Haskell linear algebra library that has the following features: Matrix multiplication Matrix addition Matrix transposition Rank calculation Matrix inversion is a plus and has the following properties: arbitrary element (scalar) types (in particular element types that are not Storable instances). My elements are an instance of Num, additionally the multiplicative inverse can be calculated. The elements mathematically form a finite field (??2256). That should be enough to implement the features mentioned above. arbitrary matrix sizes (I'll probably need something like 100x100, but the matrix sizes will depend on the user's input so it should not be limited by anything else but the memory or the computational power available) as fast as possible, but I'm aware that a library for arbitrary elements will probably not perform like a C/Fortran library that does the work (interfaced via FFI) because of the indirection of arbitrary (non Int, Double or similar) types. At least one pointer gets dereferenced when an element is touched (written in Haskell, this is not a real requirement for me, but since my elements are no Storable instances the library has to be written in Haskell) I already tried very hard and evaluated everything that looked promising (most of the libraries on Hackage directly state that they wont work for me). In particular I wrote test code using: hmatrix, assumes Storable elements Vec, but the documentation states: Low Dimension : Although the dimensionality is limited only by what GHC will handle, the library is meant for 2,3 and 4 dimensions. For general linear algebra, check out the excellent hmatrix library and blas bindings I looked into the code and the documentation of many more libraries but nothing seems to suit my needs :-(. Update Since there seems to be nothing, I started a project on GitHub which aims to develop such a library. The current state is very minimalistic, not optimized for speed at all and only the most basic functions have tests and therefore should work. But should you be interested in using or helping out developing it: Contact me (you'll find my mail address on my web site) or send pull requests.

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  • JavaScript computer algebra system

    - by Jonas
    I am looking for a simple computer algebra system (cas) for JavaScript but I can't find anything with google. I only need basic functionality: simplify expressions to some canonic form. Ability to check if two expressions are the same, i.e., a(x+y) == ax+ay parse mathematical formulas. I want it to be able to read expressions like ax²+4x. solve simple equations etc. Do you know of such a library?

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  • Converting a certain SQL query into relational algebra

    - by Fumler
    Just doing an assignment for my database course and I just want to double check that I've correctly wrapped my head around relational algebra. The SQL query: SELECT dato, SUM(pris*antall) AS total FROM produkt, ordre WHERE ordre.varenr = produkt.varenr GROUP BY dato HAVING total >= 10000 The relational algebra: stotal >= 10000( ?R(dato, total)( sordre.varenr = produkt.varenr( datoISUM(pris*antall(produkt x ordre)))) Is this the correct way of doing it?

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  • Relational algebra help?!

    - by Tom
    im new to relational algebra and finding it difficult. Ive answered a few questions, however they where relatively simple. Could do with help with these though. Database Patient (PatientCode, PatientSurname, PatientFirstname, PatientSex, PatientAge, PatientOccupation, PatientHeight, PatientWeight, PatientAddress) Doctor (DoctorCode, DoctorSurName, DoctorFirstName, DoctorPrivateAddress, MobileNo, Doctor Specilisim) Operation (Operation Code, PatientCode, DoctorCode, Date, Time, Result, OperationType) Is_Seen_By (PatientCode, DoctorCode, Date, Time). Q1. Find the surname and gender of the patients that have been operated on by doctor "DR333" and results have not been successful. Q2. Find the code of the operations that have been done on the 18th of November 2010 and have been successful, please also list the name of the doctors which were involved with the operation.

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  • Boolean algebra simplification

    - by xbonez
    I need to reduce this boolean expression to its simplest form. Its given that the simplest form contains 3 terms and 7 literals. The expression is: x'yz + w'x'z + x'y + wxy + w'y'z We tried this in class, and even out recitation teacher could not figure it out. Any help would be appreciated.

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  • Unexpected result in C algebra for search algorithm.

    - by Rhys
    Hi, I've implemented this search algorithm for an ordered array of integers. It works fine for the first data set I feed it (500 integers), but fails on longer searches. However, all of the sets work perfectly with the other four search algorithms I've implemented for the assignment. This is the function that returns a seg fault on line 178 (due to an unexpected negative m value). Any help would be greatly appreciated. CODE: 155 /* perform Algortihm 'InterPolationSearch' on the set 156 * and if 'key' is found in the set return it's index 157 * otherwise return -1 */ 158 int 159 interpolation_search(int *set, int len, int key) 160 { 161 int l = 0; 162 int r = len - 1; 163 int m; 164 165 while (set[l] < key && set[r] >= key) 166 { 167 168 printf ("m = l + ((key - set[l]) * (r - l)) / (set[r] - set[l])\n"); 169 170 printf ("m = %d + ((%d - %d) * (%d - %d)) / (%d - %d);\n", l, key, set[l], r, l, set[r], set[l]); 171 m = l + ((key - set[l]) * (r - l)) / (set[r] - set[l]); 172 printf ("m = %d\n", m); 173 174 #ifdef COUNT_COMPARES 175 g_compares++; 176 #endif 177 178 if (set[m] < key) 179 l = m + 1; 180 else if (set[m] > key) 181 r = m - 1; 182 else 183 return m; 184 } 185 186 if (set[l] == key) 187 return l; 188 else 189 return -1; 190 } OUTPUT: m = l + ((key - set[l]) * (r - l)) / (set[r] - set[l]) m = 0 + ((68816 - 0) * (100000 - 0)) / (114836 - 0); m = -14876 Thankyou! Rhys

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  • A question on nature of generated assembly in C++ and code Algebra

    - by Reetesh Mukul
    I wrote this code: #include <iostream> int main() { int a; std::cin >> a; if(a*a== 3){ std::cout << a; } return 0; } On MSVC I turned ON all optimization flags. I expected that since a*a can never be 3, so compiler should not generate code for the section: if(a*a== 3){ std::cout << a; } However it generated code for the section. I did not check GCC or LLVM/CLang. What are the limits of expectation from a C++ compiler in these scenarios?

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  • linear algebra libraries for clusters

    - by Abruzzo Forte e Gentile
    Hi all I need to develop applications doing linear algebra + eigenvalue + linear equation solutions over a cluster of pcs ( I have a lot of machines available ). I discovered Scalapack libraries but they seem to me developed long time ago. Do you know if these are other libs available that I should learn doing math & linear algebra in a cluster? My language is C++ and off course I am newbie to this topic. Kind Regards to everybody AFG

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  • How can I split Excel data from one row into multiple rows

    - by Lenny
    Good afternoon, Is there a way to split data from one row and store to separate rows? I have a large file that contains scheduling information and I'm trying to develop a list that comprises each combination of course, day, term and period per line. For example I have a file similiar to this: Crs:Sn Title Tchr TchrName Room Days Terms Periods 7014:01 English I 678 JUNG 300 M,T,W,R,F 3,4 2,3 1034:02 English II 123 MOORE 352 M,T,W,R,F 3 4 7144:02 Algebra 238 VYSOTSKY 352 M,T,W,R,F 3,4 3,4 0180:06 Pub Speaking 23 ROSEN 228 M,T,W,R,F 3,4 5 7200:03 PE I 244 HARILAOU GYM 4 M,T,W,R,F 1,2,3 3 2101:01 Physics/Lab 441 JONES 348 M,T,W,R,F 1,2,3,4 2,3 Should extract to this in an excel file: Crs:Sn Title Tchr# Tchr Room Days Terms Period 7014:01 English I 678 JUNG 300 M 3 2 7014:01 English I 678 JUNG 300 T 3 2 7014:01 English I 678 JUNG 300 W 3 2 7014:01 English I 678 JUNG 300 R 3 2 7014:01 English I 678 JUNG 300 F 3 2 7014:01 English I 678 JUNG 300 M 4 2 7014:01 English I 678 JUNG 300 T 4 2 7014:01 English I 678 JUNG 300 W 4 2 7014:01 English I 678 JUNG 300 R 4 2 7014:01 English I 678 JUNG 300 F 4 2 7014:01 English I 678 JUNG 300 M 3 3 7014:01 English I 678 JUNG 300 T 3 3 7014:01 English I 678 JUNG 300 W 3 3 7014:01 English I 678 JUNG 300 R 3 3 7014:01 English I 678 JUNG 300 F 3 3 7014:01 English I 678 JUNG 300 M 4 3 7014:01 English I 678 JUNG 300 T 4 3 7014:01 English I 678 JUNG 300 W 4 3 7014:01 English I 678 JUNG 300 R 4 3 7014:01 English I 678 JUNG 300 F 4 3 1034:02 English II 123 MOORE 352 M 3 4 1034:02 English II 123 MOORE 352 T 3 4 1034:02 English II 123 MOORE 352 W 3 4 1034:02 English II 123 MOORE 352 R 3 4 1034:02 English II 123 MOORE 352 F 3 4 7144:02 Algebra 238 VYSOTSKY 352 M 3 3 7144:02 Algebra 238 VYSOTSKY 352 T 3 3 7144:02 Algebra 238 VYSOTSKY 352 W 3 3 7144:02 Algebra 238 VYSOTSKY 352 R 3 3 7144:02 Algebra 238 VYSOTSKY 352 F 3 3 7144:02 Algebra 238 VYSOTSKY 352 M 4 3 7144:02 Algebra 238 VYSOTSKY 352 T 4 3 7144:02 Algebra 238 VYSOTSKY 352 W 4 3 7144:02 Algebra 238 VYSOTSKY 352 R 4 3 7144:02 Algebra 238 VYSOTSKY 352 F 4 3 7144:02 Algebra 238 VYSOTSKY 352 M 3 4 7144:02 Algebra 238 VYSOTSKY 352 T 3 4 7144:02 Algebra 238 VYSOTSKY 352 W 3 4 7144:02 Algebra 238 VYSOTSKY 352 R 3 4 7144:02 Algebra 238 VYSOTSKY 352 F 3 4 7144:02 Algebra 238 VYSOTSKY 352 M 4 4 7144:02 Algebra 238 VYSOTSKY 352 T 4 4 7144:02 Algebra 238 VYSOTSKY 352 W 4 4 7144:02 Algebra 238 VYSOTSKY 352 R 4 4 7144:02 Algebra 238 VYSOTSKY 352 F 4 4 0180:06 Pub Speaking 23 ROSEN 228 M 3 5 0180:06 Pub Speaking 23 ROSEN 228 T 3 5 0180:06 Pub Speaking 23 ROSEN 228 W 3 5 0180:06 Pub Speaking 23 ROSEN 228 R 3 5 0180:06 Pub Speaking 23 ROSEN 228 F 3 5 0180:06 Pub Speaking 23 ROSEN 228 M 4 5 0180:06 Pub Speaking 23 ROSEN 228 T 4 5 0180:06 Pub Speaking 23 ROSEN 228 W 4 5 0180:06 Pub Speaking 23 ROSEN 228 R 4 5 0180:06 Pub Speaking 23 ROSEN 228 F 4 5 7200:03 PE I 244 HARILAOU GYM 4 M 1 3 7200:03 PE I 244 HARILAOU GYM 4 M 2 3 7200:03 PE I 244 HARILAOU GYM 4 M 3 3 7200:03 PE I 244 HARILAOU GYM 4 T 1 3 7200:03 PE I 244 HARILAOU GYM 4 T 2 3 7200:03 PE I 244 HARILAOU GYM 4 T 3 3 7200:03 PE I 244 HARILAOU GYM 4 W 1 3 7200:03 PE I 244 HARILAOU GYM 4 W 2 3 7200:03 PE I 244 HARILAOU GYM 4 W 3 3 7200:03 PE I 244 HARILAOU GYM 4 R 1 3 7200:03 PE I 244 HARILAOU GYM 4 R 2 3 7200:03 PE I 244 HARILAOU GYM 4 R 3 3 7200:03 PE I 244 HARILAOU GYM 4 F 1 3 7200:03 PE I 244 HARILAOU GYM 4 F 2 3 7200:03 PE I 244 HARILAOU GYM 4 F 3 3 2101:01 Physics/Lab 441 JONES 348 M 1 2 2101:01 Physics/Lab 441 JONES 348 M 2 2 2101:01 Physics/Lab 441 JONES 348 M 3 2 2101:01 Physics/Lab 441 JONES 348 M 4 2 2101:01 Physics/Lab 441 JONES 348 T 1 2 2101:01 Physics/Lab 441 JONES 348 T 2 2 2101:01 Physics/Lab 441 JONES 348 T 3 2 2101:01 Physics/Lab 441 JONES 348 T 4 2 2101:01 Physics/Lab 441 JONES 348 W 1 2 2101:01 Physics/Lab 441 JONES 348 W 2 2 2101:01 Physics/Lab 441 JONES 348 W 3 2 2101:01 Physics/Lab 441 JONES 348 W 4 2 2101:01 Physics/Lab 441 JONES 348 R 1 2 2101:01 Physics/Lab 441 JONES 348 R 2 2 2101:01 Physics/Lab 441 JONES 348 R 3 2 2101:01 Physics/Lab 441 JONES 348 R 4 2 2101:01 Physics/Lab 441 JONES 348 F 1 2 2101:01 Physics/Lab 441 JONES 348 F 2 2 2101:01 Physics/Lab 441 JONES 348 F 3 2 2101:01 Physics/Lab 441 JONES 348 F 4 2 2101:01 Physics/Lab 441 JONES 348 M 1 3 2101:01 Physics/Lab 441 JONES 348 M 2 3 2101:01 Physics/Lab 441 JONES 348 M 3 3 2101:01 Physics/Lab 441 JONES 348 M 4 3 2101:01 Physics/Lab 441 JONES 348 T 1 3 2101:01 Physics/Lab 441 JONES 348 T 2 3 2101:01 Physics/Lab 441 JONES 348 T 3 3 2101:01 Physics/Lab 441 JONES 348 T 4 3 2101:01 Physics/Lab 441 JONES 348 W 1 3 2101:01 Physics/Lab 441 JONES 348 W 2 3 2101:01 Physics/Lab 441 JONES 348 W 3 3 2101:01 Physics/Lab 441 JONES 348 W 4 3 2101:01 Physics/Lab 441 JONES 348 R 1 3 2101:01 Physics/Lab 441 JONES 348 R 2 3 2101:01 Physics/Lab 441 JONES 348 R 3 3 2101:01 Physics/Lab 441 JONES 348 R 4 3 2101:01 Physics/Lab 441 JONES 348 F 1 3 2101:01 Physics/Lab 441 JONES 348 F 2 3 2101:01 Physics/Lab 441 JONES 348 F 3 3 2101:01 Physics/Lab 441 JONES 348 F 4 3 I'm trying to avoid going line by line separating the data. I'm not well versed on the VBA functionality of Excel, but would like to get started using it. Any help would be greatly appreciated.

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  • Rewrite probabilities as boolean algebra

    - by Magsol
    I'm given three binary random variables: X, Y, and Z. I'm also given the following: P(Z | X) P(Z | Y) P(X) P(Y) I'm then supposed to determine whether or not it is possible to find P(Z | Y, X). I've tried rewriting the solution in the form of Bayes' Theorem and have gotten nowhere. Given that these are boolean random variables, is it possible to rewrite the system in terms of boolean algebra? I understand that the conditionals can be mapped to boolean implications (x -> y, or !x + y), but I'm unsure how this would translate in terms of the overall problem I'm trying to solve. (yes, this is a homework problem, but here I'm much more interested in how to formally solve this problem than what the solution is...I also figured this question would be entirely too simple for MathOverflow)

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  • How to implement a simple bullet trajectory

    - by AirieFenix
    I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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  • Best way to implement a simple bullet trajectory

    - by AirieFenix
    I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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  • How can calculus and linear algebra be useful to a system programmer?

    - by Victor
    I found a website saying that calculus and linear algebra are necessary for System Programming. System Programming, as far as I know, is about osdev, drivers, utilities and so on. I just can't figure out how calculus and linear algebra can be helpful on that. I know that calculus has several applications in science, but in this particular field of programming I just can't imagine how calculus can be so important. The information was on this site: http://www.wikihow.com/Become-a-Programmer Edit: Some answers here are explaining about algorithm complexity and optimization. When I made this question I was trying to be more specific about the area of System's Programming. Algorithm complexity and optimization can be applied to any area of programming not just System's Programming. That may be why I wasn't able to came up with such thinking at the time of the question.

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  • Mathematics for Computer Science Students

    - by Ender
    To cut a long story short, I am a CS student that has received no formal Post-16 Maths education for years. Right now even my Algebra is extremely rusty and I have a couple of months to shape up my skills. I've got a couple of video lectures in my bookmarks, consisting of: Pre-Calculus Algebra Calculus Probability Introduction to Statistics Differential Equations Linear Algebra My aim as of today is to be able to read the CLRS book Introduction to Algorithms and be able to follow the Mathematical notation in that, as well as being able to confidently read and back-up any arguments written in Mathematical notation. Aside from these video lectures, can anyone recommend any good books to help teach someone wishing to go from a low-foundation level to a more advanced level of Mathematics? Just as a note, I've taken a first-year module in Analytical Modelling, so I understand some of the basic concepts of Discrete Mathematics. EDIT: Just a note to those that are looking to learn Linear Algebra using the Video Lectures I have posted up. Peteris Krumins' Blog contains a run-through of these lecture notes as well as his own commentary and lecture notes, an invaluable resource for those looking to follow the lectures too.

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  • Points on lines where the two lines are the closest together

    - by James Bedford
    Hey guys, I'm trying to find the points on two lines where the two lines are the closest. I've implemented the following method (Points and Vectors are as you'd expect, and a Line consists of a Point on the line and a non-normalized direction Vector from that point): void CDClosestPointsOnTwoLines(Line line1, Line line2, Point* closestPoints) { closestPoints[0] = line1.pointOnLine; closestPoints[1] = line2.pointOnLine; Vector d1 = line1.direction; Vector d2 = line2.direction; float a = d1.dot(d1); float b = d1.dot(d2); float e = d2.dot(d2); float d = a*e - b*b; if (d != 0) // If the two lines are not parallel. { Vector r = Vector(line1.pointOnLine) - Vector(line2.pointOnLine); float c = d1.dot(r); float f = d2.dot(r); float s = (b*f - c*e) / d; float t = (a*f - b*c) / d; closestPoints[0] = line1.positionOnLine(s); closestPoints[1] = line2.positionOnLine(t); } else { printf("Lines were parallel.\n"); } } I'm using OpenGL to draw three lines that move around the world, the third of which should be the line that most closely connects the other two lines, the two end points of which are calculated using this function. The problem is that the first point of closestPoints after this function is called will lie on line1, but the second point won't lie on line2, let alone at the closest point on line2! I've checked over the function many times but I can't see where the mistake in my implementation is. I've checked my dot product function, scalar multiplication, subtraction, positionOnLine() etc. etc. So my assumption is that the problem is within this method implementation. If it helps to find the answer, this is function supposed to be an implementation of section 5.1.8 from 'Real-Time Collision Detection' by Christer Ericson. Many thanks for any help!

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  • Working with Temporal Data in SQL Server

    - by Dejan Sarka
    My third Pluralsight course, Working with Temporal Data in SQL Server, is published. I am really proud on the second part of the course, where I discuss optimization of temporal queries. This was a nearly impossible task for decades. First solutions appeared only lately. I present all together six solutions (and one more that is not a solution), and I invented four of them. http://pluralsight.com/training/Courses/TableOfContents/working-with-temporal-data-sql-server

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  • How to detect 2D line on line collision?

    - by Vish
    I'm a flash actionscript game developer who is a bit backward with mathematics, though I find physics both interesting and cool. For reference this is a similar game to the one I'm making: Untangled flash game I have made an untangled game almost to full completion of logic. But, when two lines intersect, I need those intersected or 'tangled' lines to show a different color; red. It would be really kind of you people if you could suggest an algorithm with/without math for detecting line segment collisions. I'm basically a person who likes to think 'visually' than 'arithmetically' :) P.S I'm trying to make a function as private function isIntersecting(A:Point, B:Point, C:Point, D:Point):Boolean Thanks in advance.

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  • Detect line line collision in an Untangled game

    - by Vish
    Pardon me if this is a repeat question,but I've been searching google for vain since the past few days, I'm a flash actionscript game developer who is a bit backward with mathematics, though I find physics both interesting and cool. Similiar game : Untangled flash game I have made an untangled game almost to full completion of logic. But, when two lines intersect , I need those intersected or 'tangled' lines to show a different color; red. It would be really kind of you people if you could suggest an algorithm with / without math for detecting line segment collisions. I'm basically a person who likes to think 'visually' than 'arithmetically' :) P.S I'm trying to make a function as private function isIntersecting(A:Point, B:Point, C:Point, D:Point):Boolean Thanks in advance. Vishnu Ajit

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  • Raycasting tutorial / vector math question

    - by mattboy
    I'm checking out this nice raycasting tutorial at http://lodev.org/cgtutor/raycasting.html and have a probably very simple math question. In the DDA algorithm I'm having trouble understanding the calcuation of the deltaDistX and deltaDistY variables, which are the distances that the ray has to travel from 1 x-side to the next x-side, or from 1 y-side to the next y-side, in the square grid that makes up the world map (see below screenshot). In the tutorial they are calculated as follows, but without much explanation: //length of ray from one x or y-side to next x or y-side double deltaDistX = sqrt(1 + (rayDirY * rayDirY) / (rayDirX * rayDirX)); double deltaDistY = sqrt(1 + (rayDirX * rayDirX) / (rayDirY * rayDirY)); rayDirY and rayDirX are the direction of a ray that has been cast. How do you get these formulas? It looks like pythagorean theorem is part of it, but somehow there's division involved here. Can anyone clue me in as to what mathematical knowledge I'm missing here, or "prove" the formula by showing how it's derived?

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