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  • Are all the system's floating points operations the same?

    - by Jj
    We're making this web app in PHP and when working in the reports we have Excel files to compare our results to make sure our coding is doing the right operations. Now we're running into some differences due floating point arithmetics. We're doing the same divisions and multiplications and running into slightly different numbers, that add up to a notable difference. My question is if Excel is delegating it's floating point arithmetic to the CPU and PHP is also relying in the CPU for it's operations. Or does each application implements its own set of math algorithms?

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  • Explicitly multiplying values as longs

    - by Bill Szerdy
    I understand that all math is done as the largest data type required to handle the current values but when you transverse a loop how do you explicitly multiply longs? The following code returns 0, I suspect, because of an overflow. long result = 0L; List<Long> temp = (List<Long>) getListOfIntegers(); for (int i = 0; i < temp.size(); i++) { result *= temp.get(i).longValue(); } System.out.println(result);

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  • What's a better choice for SQL-backed number crunching - Ruby 1.9, Python 2, Python 3, or PHP 5.3?

    - by Ivan
    Crterias of 'better': fast im math and simple (little of fields, many records) db transactions, convenient to develop/read/extend, flexible, connectible. The task is to use a common web development scripting language to process and calculate long time series and multidimensional surfaces (mostly selectint/inserting sets of floats and dong maths with rhem). The choice is Ruby 1.9, Python 2, Python 3, PHP 5.3, Perl 5.12, JavaScript (node.js). All the data is to be stored in a relational database (due to its heavily multidimensional nature), all the communication with outer world is to be done by means of web services.

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  • Calculate proportional width of object (proportion: 1600x1080)

    - by Hans Stauden
    Hello, this jquery question: when I set a specific height to a "#div", i want to set the width of a inner object automatically too (cause i need a width to read it out) [ "#div" ["object"] ] example: (object).css(width: [ CALCULATION ], height: ($("#div").height())+'px' ) the original proportion of the image is: 1600x1080 here's the link to the attachment, take a look at it (tinypic): link text the heights "500px", "600px" and "700px" you can see in the attachment are just examples, the heigth could also be "711px", "623px", "998px" etc. cause the "#div" scales with the browser (i can read out the height of window, that works) my math skills aren't really good, would be great if someone could help me out :-)

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  • How do you create a formula that has diminishing returns?

    - by egervari
    I guess this is a math question and not a programming question, but what is a good way to create a formula that has diminishing returns? Here are some example points on how I want the curve to look like. f(1) = 1 f(1.5)= .98 f(2) = .95 f(2.5) = .9 f(3) = .8 f(4) = .7 f(5) = .6 f(10) = .5 f(20) = .25 Notice that as the input gets higher, the percentage decreases rapidly. Is there any way to model a function that has a very smooth and accurate curve that says this? Another way to say it is by using a real example. You know in Diablo II they have Magic Find? There are diminishing returns for magic find. If you get 100%, the real magic find is still 100%. But the more get, your actual magic find goes down. So much that say if you had 1200, your real magic find is probably 450%. So they have a function like: actualMagicFind(magicFind) = // some way to reduced magic find

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  • Obtain Latitude and Longitude from a GeoTIFF File

    - by Mikee
    Using GDAL in Python, how do you get the latitude and longitude of a GeoTIFF file? GeoTIFF's do not appear to store any coordinate information. Instead, they store the XY Origin coordinates. However, the XY coordinates do not provide the latitude and longitude of the top left corner and bottom left corner. It appears I will need to do some math to solve this problem, but I don't have a clue on where to start. What procedure is required to have this performed? I know that the GetGeoTransform() method is important for this, however, I don't know what to do with it from there.

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  • Fastest implementation of the frac function in C#

    - by user349937
    I would like to implement a frac function in C# (just like the one in hsl here http://msdn.microsoft.com/en-us/library/bb509603%28VS.85%29.aspx) but since it is for a very processor intensive application i would like the best version possible. I was using something like public float Frac(float value) { return value - (float)Math.Truncate(value); } but I'm having precision problems, for example for 2.6f it's returning in the unit test Expected: 0.600000024f But was: 0.599999905f I know that I can convert to decimal the value and then at the end convert to float to obtain the correct result something like this: public float Frac(float value) { return (float)((decimal)value - Decimal.Truncate((decimal)value)); } But I wonder if there is a better way without resorting to decimals...

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  • Using exponential smoothing with NaN values

    - by Eric
    I have a sample of some kind that can create somewhat noisy output. The sample is the result of some image processing from a camera, which indicates the heading of a blob of a certain color. It is an angle from around -45° to +45°, or a NaN, which means that the blob is not actually in view. In order to combat the noisy data, I felt that exponential smoothing would do the trick. However, I'm not sure how to handle the NaN values. On the one hand, involving them in the math would result in a NaN average, which would then prevent any meaningful results. On the other hand, ignoring NaN values completely would mean that a "no-detection" scenario would never be reported. And just to complicate things, the data is also noisy in that it can get false NaN value, which ideally would be smoothed somehow to prevent random noise. Any ideas about how I could implement such an exponential smoother?

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  • Android: Constructing a triangle based on Geographical information

    - by Aidan
    Hi Guys, I'm constructing a geolocation based application and I'm trying to figure out a way to make my application realise when a user is facing the direction of the given location (a particular long / lat co-ord). I've got the math figured, I just have the triangle to construct. Here's a further clarification of what I want to do.. I just want to know is there a way to get java to construct 2 other co-ordinates based on my orientation in relation to true north and my current co-ordinate? I'd like to construct a tri-angle, 45 degrees out each way of my current location (one of the points) and 1 kilometer in that direction. The problem is I don't know how to make Android/Java recognise that I want to find that point in the direction I'm currently facing.. Anyone got any ideas?

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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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  • Best way to search for a saturation value in a sorted list

    - by AB Kolan
    A question from Math Battle. This particular question was also asked to me in one of my job interviews. " A monkey has two coconuts. It is fooling around by throwing coconut down from the balconies of M-storey building. The monkey wants to know the lowest floor when coconut is broken. What is the minimal number of attempts needed to establish that fact? " Conditions: if a coconut is broken, you cannot reuse the same. You are left with only with the other coconut Possible approaches/strategies I can think of are Binary break ups & once you find the floor on which the coconut breaks use upcounting from the last found Binary break up lower index. Window/Slices of smaller sets of floors & use binary break up within the Window/Slice (but on the down side this would require a Slicing algorithm of it's own.) Wondering if there are any other way to do this.

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  • Sliding & Fading controls on a C# form

    - by Tommy
    Hey there, I'm trying to implement a way to slide&fade controls around (more than one at the same time possibly) elegantly. So in other words, say i had a picture in the top left corner, and a texbox in the bottom right corner, i'd like to be able to have them slide. not just snap. slide, to the opposite corners and replace eachothers position. Ive been working for awhile but have not come up with anything efficient, even just some of the basic math calculations would be a great start.

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  • Require help with program for edutainment game

    - by Ender
    I am working on a factorisation problem and for small numbers it is working well. I've been able to calculate the factors (getting the answers from Wolfram Alpha) for small numbers, like the one on the Wikipedia page (5959). Along with the Wikipedia page I have been following this guide. Once again, as my Math knowledge is pretty poor I cannot follow what I need to do next. EDIT: It finally works! I'll post the working code up here once I've got it fully working so that others in my predicament can learn from it.

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  • How to Parse 'Mathy' Stuff...

    - by Rob P.
    Please forgive my title, I really don't know how to phrase it better. This isn't a school assignment or anything, but I realize it's a mostly academic question. But, what I've been struggling to do is parse 'math' text and come up with an answer. For Example - I can figure out how to parse '5 + 5' or '3 * 5' - but I fail when I try to correctly chain operations together. (5 + 5) * 3 It's mostly just bugging me that I can't figure it out. If anyone can point me in a direction, I'd really appreciate it.

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  • How to add Transparency information to a HEX color code?

    - by TK123
    I have to modify some code and the previous developer left this comment: color: color, // e.g. '#RRGGBBFF' - Last 2 digits are alpha information On the page there is a color picker that let's the user change text color. It gives HEX values like so: #RRGGBB And there is a slider that allows the user to change a text's transparency. It runs from 0.1 to 1 Somehow I need to get a 2 digit letter from this transparency amount and append it to the HEX value for it to work. Does anyone know how to append Alpga information to HEX color codes? What is the math formula for it? I guess the question can also be answered if anyone knows how to concert RGBA color values with transparency into HEX: rgba(255, 255, 255, 0.6)

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  • Randomly generating sequence of ints in a specific range

    - by vvv
    Hi, I am unsure how to put this and my math skills aren't that strong. But here's what I need. I want to generate a list of all the 16bit integers (0-65535). But everytime I do so I want to seed the algorithm randomly that each time the list starts with a different integer and all the subsequent integers will be generated once but also in random order. small example (1-5): ... 1, 5, 3, 2, 4 4, 3, 1, 5, 2 2, 1, 4, 5, 3 ... Any help?

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  • recursive enumeration of integer subsets?

    - by KDaker
    I have an NSArray of NSNumbers with integer values such as [1,10,3]. I want to get the sum of all the possible subsets of these numbers. For example for 1,10 and 3 i would get: 1, 10, 3, 1+10=11, 1+3=4, 10+3=13, 1+10+3=14 there are 2^n possible combinations. I understand the math of it but im having difficulties putting this into code. so how can i put this into a method that would take the initial array of numbers and return an array with all the sums of the subsets? e.g -(NSArray *) getSums:(NSArray *)numbers; I understand that the results grow exponentially but im going to be using it for small sets of numbers.

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  • Getting the fractional part of a float without using modf()

    - by knight666
    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 using my Frac() and InvFrac() functions to draw an anti-aliased line. Using modf I get a perfectly smooth line. With my own method pixels start jumping around due to precision loss. This is my code: const float fp_amount = (float)(0xFFFF); const float fp_amount_inv = 1.f / fp_amount; inline float Frac(float a_X) { return ((int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } inline float Frac(float a_X) { return (0xFFFF - (int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } Thanks in advance!

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  • Mathematics and Game Programming

    - by Xfcn
    I want to program graphical 2D games more complex than the basic 2D stuff I already know. I don't want to do 3D programming. Just more complex 2D stuff. I dropped high school before I could learn a lot of stuff so I walked away with enough algebra knowledge to balance my checkbook and do some light 2D Cartesian programming. Are there any good resources out there for a guy with a limited attention span (say 20 minutes apiece for a subject I'm keenly interested in) to learn, gradually, how to do something more useful with math in programming?

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  • Mathematically Find Max Value without Conditional Comparison

    - by Cnich
    ----------Updated ------------ codymanix and moonshadow have been a big help thus far. I was able to solve my problem using the equations and instead of using right shift I divided by 29. Because with 32bits signed 2^31 = overflows to 29. Which works! Prototype in PHP $r = $x - (($x - $y) & (($x - $y) / (29))); Actual code for LEADS (you can only do one math function PER LINE!!! AHHHH!!!) DERIVDE1 = IMAGE1 - IMAGE2; DERIVED2 = DERIVED1 / 29; DERIVED3 = DERIVED1 AND DERIVED2; MAX = IMAGE1 - DERIVED3; ----------Original Question----------- I don't think this is quite possible with my application's limitations but I figured it's worth a shot to ask. I'll try to make this simple. I need to find the max values between two numbers without being able to use a IF or any conditional statement. In order to find the the MAX values I can only perform the following functions Divide, Multiply, Subtract, Add, NOT, AND ,OR Let's say I have two numbers A = 60; B = 50; Now if A is always greater than B it would be simple to find the max value MAX = (A - B) + B; ex. 10 = (60 - 50) 10 + 50 = 60 = MAX Problem is A is not always greater than B. I cannot perform ABS, MAX, MIN or conditional checks with the scripting applicaiton I am using. Is there any way possible using the limited operation above to find a value VERY close to the max?

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  • Learning AES: the KeyBytes

    - by Tom Brito
    I got the following example from here: import java.security.Security; import javax.crypto.Cipher; import javax.crypto.spec.SecretKeySpec; public class MainClass { public static void main(String[] args) throws Exception { Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider()); byte[] input = "www.java2s.com".getBytes(); byte[] keyBytes = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17 }; SecretKeySpec key = new SecretKeySpec(keyBytes, "AES"); Cipher cipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC"); System.out.println(new String(input)); // encryption pass cipher.init(Cipher.ENCRYPT_MODE, key); byte[] cipherText = new byte[cipher.getOutputSize(input.length)]; int ctLength = cipher.update(input, 0, input.length, cipherText, 0); ctLength += cipher.doFinal(cipherText, ctLength); System.out.println(new String(cipherText)); System.out.println(ctLength); // decryption pass cipher.init(Cipher.DECRYPT_MODE, key); byte[] plainText = new byte[cipher.getOutputSize(ctLength)]; int ptLength = cipher.update(cipherText, 0, ctLength, plainText, 0); ptLength += cipher.doFinal(plainText, ptLength); System.out.println(new String(plainText)); System.out.println(ptLength); } } I imagine that the byte[] keyBytes should be random generated, so I gone to test the max size before do it. When adding one more byte 0x18 to the array, the exception raised: InvalidKeyException: Key length not 128/192/256 bits. But the original 18 bytes (from 0 to 17) are not multiple of nither 128, 192 or 256. I would like to understand the math here.. can anyone explain me? Thanks!

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  • A function where small changes in input always result in large changes in output

    - by snowlord
    I would like an algorithm for a function that takes n integers and returns one integer. For small changes in the input, the resulting integer should vary greatly. Even though I've taken a number of courses in math, I have not used that knowledge very much and now I need some help... An important property of this function should be that if it is used with coordinate pairs as input and the result is plotted (as a grayscale value for example) on an image, any repeating patterns should only be visible if the image is very big. I have experimented with various algorithms for pseudo-random numbers with little success and finally it struck me that md5 almost meets my criteria, except that it is not for numbers (at least not from what I know). That resulted in something like this Python prototype (for n = 2, it could easily be changed to take a list of integers of course): import hashlib def uniqnum(x, y): return int(hashlib.md5(str(x) + ',' + str(y)).hexdigest()[-6:], 16) But obviously it feels wrong to go over strings when both input and output are integers. What would be a good replacement for this implementation (in pseudo-code, python, or whatever language)?

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  • How to create a magic square in PHP?

    - by TerranRich
    I'd like to try my hand at creating a Magic Square in PHP (i.e. a grid of numbers that all add up to the same value), but I really don't know where to start. I know of the many methods that create magic square, such as starting "1" at a fixed position, then moving in a specific direction with each iteration. But that doesn't create a truly randomized Magic Square, which is what I'm aiming for. I want to be able to generate an N-by-N Magic Square of N² numbers where each row and column adds up to N(N²+1)/2 (e.g. a 5x5 square where all rows/columns add up to 65 — the diagonals don't matter). Can anybody provide a starting point? I don't want anybody to do the work for me, I just need to know how to start such a project? I know of one generator, written in Java (http://www.dr-mikes-math-games-for-kids.com/how-to-make-a-magic-square.html) but the last Java experience I had was over 10 years ago before I quickly abandoned it. Therefore, I don't really understand what the code is actually doing. I did notice, however, that when you generate a new square, it shows the numbers 1-25 (for a 5x5 square), in order, before quickly generating a fresh randomized square.

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  • Calculate total batch upload transfer percent with limited information

    - by GONeale
    Hi there, I have a system which uploads to a server file by file and displays a progress bar on file upload progress, then underneath a second progress bar which I want to indicate percentage of batch complete across all files queued to upload. Information and algorithms I can work out are: Bytes Sent / Total Bytes To Send = First progress bar (eg. 512KB of 1024KB (50%)) That works fine. However supposing I have two other files left to upload, but both file sizes are unknown (as this is only known once the file is about to commence upload, at which point it is compressed and file size is determined) how would I go about making my third progress bar? I didn't think this would be possible as I would need "Total Bytes Sent" / "Total Bytes To Send", to replicate the logic of my first progress bar on a larger scale, however I did get a version working: "Current file number we are on" / "total number of files to send" returning the percentage through the batch, however obviously will not incrementally update and it's pretty crude. So on further thinking I thought if I could incorporate the current file % with this algorithm I could perhaps get the correct progress percentage of my batch's current point. I tried this algorithm, but alas to no such avail (sorry to any math heads, it's probably quite apparent why it won't work) ("Current file number we are on" / "total number of files to send") * ("Bytes Sent" / "Total Bytes To Send") For example I thought I was on the right track when testing with this example: 2/3 (2nd of 3rd file) = 66% (this is right so far) but then when I added * 0.20 (for indicating only 20% of 2nd file has uploaded) we went back to 13%. What I need is only a little over 33%! I did try the inverse at 0.80 and a (2/3 * (2/3 * 0.2)) Can this be done without knowing entire bytes in batch to upload? Please help! Thank you!

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  • php calculate float HELP!!

    - by apis17
    help!! i have weird math calculation here. hope someone will explain. $a = 1.85/100; $b = 1.5/100; $c = 1.1/100; $d = 0.4/100; $e = 0.4/100; $f = 0.4/100; $g = 0.4/100; $h = $a + $b + $c + $d + $e + $f + $g; echo $h*100 ."<br>"; $i = $h-$a; $i = $i-$b; $i = $i-$c; $i = $i-$d; $i = $i-$e; $i = $i-$f; $i = $i-$g; echo $i; last $i value should be 0 but it returns 6.93889390391E-18

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