number squared in programming
I know this is probably a very simple question but how would I do something like n2 in a programming language? Is it n * n? Or is there another way? ...
math
Fastest algorithm for primality test
I need to test primality on intervals between numbers which are really big (in the range of long long), so i need some fast algorithm for checking if a number is prime or not. Please suggest your ideas. ...
circles and triangles problem
Hello everyone, I have an interesting problem here I've been trying to solve for the last little while: I have 3 circles on a 2D xy plane, each with the same known radius. I know the coordinates of each of the three centers (they are arbitrary and can be anywhere). What is the largest triangle that can be drawn such that each vertic...
Rewrite probabilities as boolean algebra
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 i...
Linear Regression and Java Dates
I am trying to find the linear trend line for a set of data. The set contains pairs of dates (x values) and scores (y values). I am using a version of this code as the basis of my algorithm. The results I am getting are off by a few orders of magnitude. I assume that there is some problem with round off error or overflow because I am us...
Bounding Boxes for Circle and Arcs in 3D
Given curves of type Circle and Circular-Arc in 3D space, what is a good way to compute accurate bounding boxes (world axis aligned)? Edit: found solution for circles, still need help with Arcs. C# snippet for solving BoundingBoxes for Circles: public static BoundingBox CircleBBox(Circle circle) { Point3d O = circle.Center; Vect...
Power Law distribution for a given exponent in C# using MathNet
Hello! I am currently working on a project where I need to generate multiple values (floats or doubles preferably) that follow a power law distribution with a given exponent! I was advised to use the MathNet.Iridium library to help me. The problem I have is that the documentation is not as explicit as it should be if there is any! I se...
how to find distinct digit set numbers over a range of integers?
Suppose i have a unsigned integer, call it low and one another call it high such that high>low. The problem is to find distinct digit set numbers over this range. For example, suppose low is 1 and high is 20 then the answer is 20, because all the numbers in this range are of distinct digit sets. If suppose low is 1 and high is 21, then t...
Print all ways to sum n integers so that they total a given sum.
Im trying to come up with an algorithm that will print out all possible ways to sum N integers so that they total a given value. Example. Print all ways to sum 4 integers so that they sum up to be 5. Result should be something like: 5 0 0 0 4 1 0 0 3 2 0 0 3 1 1 0 2 3 0 0 2 2 1 0 2 1 2 0 2 1 1 1 1 4 0 0 1 3 1 0 1 2 2 0 1 2...
Determine if 3D point is inside 2D Circle
Hello: I wish to determine if a Point P(x,y,z) is inside a 2D circle in 3D space defined by its center C (cx, cy, cz), radius R, and normal to the plane the circle lies on N. I know that a point P lying on a 2D circle in 3D space is defined by: P = R*cos(t)*U + R*sin(t)*( N x U ) + C where U is a unit vector from the center of the ci...
Getting the fractional part of a float without using modf()
Hi, I'm developing for a platform without a math library, so I need to build my own tools. My current way of getting the fraction is to convert the float to fixed point (multiply with (float)0xFFFF, cast to int), get only the lower part (mask with 0xFFFF) and convert it back to a float again. However, the imprecision is killing me. I'm...
Divide not returning the decimal value I expect
If you divide 2 / 3, it should return 0.66666666666666667. Instead, I get 0.0 in double value type and 0 in decimal. My purpose is to divide even (e.g. 2 / 3) and round to 1 always to the nearest. Any help? ...
Math.Round(decimal) Problem
Ok this is new, Math.Round(1.5) returns 2, i need 1. How to handle this? [EDITED] I know its the elementary default way, i need the opposite. Wrong typing meaning. Any Suggestions? ...
How to get the nth root of big numbers in C++?
Is there a C++ library that can take nth roots of big numbers (numbers than can't fit in an unsigned long long)? ...
Detecting periodic repetitions in the data stream
Let's say I have an array of zeros: a = numpy.zeros(1000) I then introduce some repetitive 'events': a[range(0, 1000, 30)] = 1 Question is, how do I detect the 'signal' there? Because it's far from the ideal signal if I do the 'regular' FFT I don't get a clear indication of where my 'true' signal is: f = abs(numpy.fft.rfft(a)) Is t...
multidimensional vector rotation and angle computation -- how?
Input: two multidimensional (for example dim=8) vectors a and b. I need to find out the "directed" angle (0-2*Pi, not 0-Pi) between those vectors a and b. And if they are not parallel I need to rotate vector b in plane a,b by "directed" angle L. If they are parallel, plane does not matter, but angle of rotation is still the same L. For...
how to determine base of a number?
Given a integer number and its reresentation in some arbitrary number system. The purpose is to find the base of the number system. For example, number is 10 and representation is 000010, then the base should be 10. Another example: number 21 representation is 0010101 then base is 2. One more example is: number is 6 and representation os...
Is it possible to add custom "napkin math" operators in OneNote 2007?
If you're not familiar with OneNote's "napkin math" feature, it allows you to type mathematical equations and have OneNote evaluate them on the fly (with a limited set of operators/functions). I'm wondering if it's possible to create my own, either through an obscure UI in OneNote, or through some sort of custom plugin that I would devel...
Help with PHP function that will take $bytes and $rate (per GB) and return $total
I was hoping someone might help with a function that given two parameters: @param $bytes : total amount in bytes of data consumed @param $rate : rate per GB, example .22 (for 22 cents) @returns Total amount owed Rounded to nearest cent of course. Thanks in advance for any help. ...
Help on understanding JS
I have thos piece of code: Math&&Math.random?Math.floor(Math.random()*10000000000000):Date.getTime(); And as far as i know && is logic operator for AND, so im trying to convert this into PHP and this is where i got: intval(floor(time()/10800000)%10+(rand()?floor(rand()*10000000000000):time())) The problem is that i can't understand...