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  • This is more a matlab/math brain teaser than a question

    - by gd047
    Here is the setup. No assumptions for the values I am using. n=2; % dimension of vectors x and (square) matrix P r=2; % number of x vectors and P matrices x1 = [3;5] x2 = [9;6] x = cat(2,x1,x2) P1 = [6,11;15,-1] P2 = [2,21;-2,3] P(:,1)=P1(:) P(:,2)=P2(:) modePr = [-.4;16] TransPr=[5.9,0.1;20.2,-4.8] pred_modePr = TransPr'*modePr MixPr = TransPr.*(modePr*(pred_modePr.^(-1))') x0 = x*MixPr Then it was time to apply the following formula to get myP , where µij is MixPr. I used this code to get it: myP=zeros(n*n,r); Ptables(:,:,1)=P1; Ptables(:,:,2)=P2; for j=1:r for i = 1:r; temp = MixPr(i,j)*(Ptables(:,:,i) + ... (x(:,i)-x0(:,j))*(x(:,i)-x0(:,j))'); myP(:,j)= myP(:,j) + temp(:); end end Some brilliant guy proposed this formula as another way to produce myP for j=1:r xk1=x(:,j); PP=xk1*xk1'; PP0(:,j)=PP(:); xk1=x0(:,j); PP=xk1*xk1'; PP1(:,j)=PP(:); end myP = (P+PP0)*MixPr-PP1 I tried to formulate the equality between the two methods and seems to be this one. To make things easier, I ignored from both methods the summation of matrix P. where the first part denotes the formula that I used, while the second comes from his code snippet. Do you think this is an obvious equality? If yes, ignore all the above and just try to explain why. I could only start from the LHS, and after some algebra I think I proved it equals to the RHS. However I can't see how did he (or she) think of it in the first place.

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  • Weird Java Math ,10 ^ 1 = 11?

    - by Simon
    For an exercise I was writing a loop that turns a string into an integer without using the built in functions by multiplying each individual value by its numerical position. 75 would be 7*(10 ^ 1) + 5*(10 ^ 0), for example. However, for some reason (10 ^ 1) keeps coming back as 11. Is there some mistake I have made or an explanation for this?

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  • Math algorithm question

    - by Senica Gonzalez
    I'm not sure if this can be done without some determining factor....but wanted to see if someone knew of a way to do this. I want to create a shifting scale for numbers. Let's say I have the number 26000. I want the outcome of this algorithm to be 6500; or 25% of the original number. But if I have the number 5000, I want the outcome to be 2500; or 50% of the original number. The percentages don't have to be exact, this is just an example. I just want to have like a sine wave sort of thing. As the input number gets higher, the output number is a lower percentage of the input. Does that make sense?

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  • Closest Approach question for math/physics heads

    - by Kyle
    I'm using a Segment to Segment closest approach method which will output the closest distance between two segments of length. These objects are moving at variable speed each, so even when it succeeds I'm currently using a 10-step method and calculating the distance between 2 spheres as they move along the two segments. So, basically the length of each segment is the object's traverse in the physics step, and the radius is the objects radius. By stepping, I can tell where they collide, and if they collide (Sort of; for the MOST part.).. I get the feeling that there could be something better. While I sort of believe that the first closest approach call is required, I think that the method immediately following it is a TAD weak. Can anyone help me out? I can illustrate this if needed. Thanks alot!

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  • Math: How to sum each row of a matrix

    - by macek
    I have a 1x8 matrix of students where each student is a 4x1 matrix of scores. Something like: SCORES S [62, 91, 74, 14] T [59, 7 , 59, 21] U [44, 9 , 69, 6 ] D [4 , 32, 28, 53] E [78, 99, 53, 83] N [48, 86, 89, 60] T [56, 71, 15, 80] S [47, 67, 79, 40] Main question: Using sigma notation, or some other mathematical function, how can I get a 1x8 matrix where each student's scores are summed? # expected result TOTAL OF SCORES S [241] T [146] U [128] D [117] E [313] N [283] T [222] S [233] Sub question. To get the average, I will multiply the matrix by 1/4. Would there be a quicker way to get the final result? AVERAGE SCORE S [60.25] T [36.50] U [32.00] D [29.25] E [78.25] N [70.75] T [55.50] S [58.25] Note: I'm not looking for programming-related algorithms here. I want to know if it is possible to represent this with pure mathematical functions alone.

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  • Some math and animation

    - by Ockonal
    Hello, I have a grass texture: I use it in my 2d-game. I want to animate it by code, without any predefined animations. The grass should interact with wind. So when the wind is stronger, the grass should stoop into need side more. First version of animation I made using sinusoid function, but such animation is a bit ugly, because the base of the grass moves left/right like all another part of picture. And with sinusoid I'm not able to regulate stoop of the image. Any advices?

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  • Math/numerical formula every computer programmer should know

    - by aaa
    This is a follow-up question to What should every programmer know and Is mathematics necessary. So the question is, as a computer programmer, what is the most important/useful mathematical or numerical formula that you use? By Formula I mean anything that involves less obvious manipulations, whenever binomial coefficients or bit hacks. I work with multidimensional arrays and various matrix representations. So for me most commonly used formulas are: A(i,j,k,..) = a[i + j*Dim0 + k*Dim0*Dim1 + ... to map indexes to one dimension ( which is basic address calculation which many people do not seem to know). And triangular number T(i) = (i*i + i)/2 which is related to binomial coefficients, used to calculate address in triangular matrixes and many other things. What is your workhorse formula that you think programmer should know?

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  • iPhone SDK math - pythagorean theorem problem!

    - by Flafla2
    Just as a practice, I am working on an app that solves the famous middle school pythagorean theorem, a squared + b squared = c squared. Unfortunately, the out-coming answer has, in my eyes, nothing to do with the actual answer. Here is the code used during the "solve" action. - (IBAction)solve { int legoneint; int legtwoint; int hypotenuseint; int lonesq = legoneint * legoneint; int ltwosq = legtwoint * legtwoint; int hyposq = hypotenuseint * hypotenuseint; hyposq = lonesq + ltwosq; if ([legone.text isEqual:@""]) { legtwoint = [legtwo.text intValue]; hypotenuseint = [hypotenuse.text intValue]; answer.text = [NSString stringWithFormat:@"%d", legoneint]; self.view.backgroundColor = [UIColor blackColor]; } if ([legtwo.text isEqual:@""]) { legoneint = [legone.text intValue]; hypotenuseint = [hypotenuse.text intValue]; answer.text = [NSString stringWithFormat:@"%d", legtwoint]; self.view.backgroundColor = [UIColor blackColor]; } if ([hypotenuse.text isEqual:@""]) { legoneint = [legone.text intValue]; legtwoint = [legtwo.text intValue]; answer.text = [NSString stringWithFormat:@"%d", hypotenuseint]; self.view.backgroundColor = [UIColor blackColor]; } } By the way, legone, legtwo, and hypotenuse all represent the UITextField that corresponds to each mathematical part of the right triangle. Answer is the UILabel that tells, you guessed it, the answer. Does anyone see any flaws in the program? Thanks in advance!

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  • How to do simple math in datagridview

    - by EB
    I am new to C#. I have a datagridview with 9 columns. I am simply trying take the value in column 5 and subtract it from column 6. Then display the result in column 9. It seems simple enough.I know it's done in excel all the time. But I just cannot figure this out. Do I need to create a new class with a method called calculate columns? or does the datagridview class have something already built in that can handle this? Again, I am new to C#. Any help would be appreciated. Thank you, Oceantrain.

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  • C# define string format of double/floats to be US english by default

    - by neil
    Hi, I have got several thousands of lines of a web application source code, initially written on a US development system, to maintain. It makes heavy use of SQL statement strings, which are combined on the fly, e.g. string SQL = "select * from table where double_value = " + Math.Round(double_value, 2); Don't comment on bad programming style, that doesn't help me in this case :) The cruix: My system uses a German locale, which in turn leads to wrong SQL statements, like this: "select * from table where double_value = 15,5" (Note the comma as decimal separator instead of a point). Question: What is the most "elegant" way to change the locale of the web app in this case) to US or UK in order to prevent being forced to change and inspect every single line of code? .net 3.5 is not an option (would give me the chance to overwrite ToString() in an extension class) Kind regards

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  • PHP math gets crazy, need explanation, my brain is melting

    - by derei
    I know that playing with php float can give strange results if you try to add "goats + apples", but please take a look to the following case: $val = 1232.81; $p1 = 1217.16; $p2 = 15.65; $sum = $p1 + $p2; $dif = $val - $sum; echo $dif; It will give you -2.2737367544323E-13 ... yeah, ALMOST zero, but then why it doesn't say 0 ? This freaks me out big time. Please, I need some valid explanation.

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  • Math Looping Between Min and Max Using Mod?

    - by TheDarkIn1978
    i'm attempting to build a tiny (or perhaps not so tiny) formula that will contain numbers between a set min and max, but also loop these numbers so they are not clipped if they are outside of the range. so far, this is what i have. min1 = 10 max1 = 90 val1 = 92 //will make 12, which is what i want since it loops formula: min(max(min1,min(val1,max1)),mod(val1,max1)+min1) however, i'd like it to loop the other direction also, so that if val1 is 5, which is -5 outside of min1, it will become 85. another problem i'm running into is that max1 % max1 != max1 as i want it to, since the max is part of the range trying to be clear, here are some examples of desired output based on a range with looping min1 = 10 max1 = 90 ---------------------------------------------- val1 = 30 //within range: stays as 30 val1 = 90 //within range: stays as 90 val1 = -6 //below range: loops to becomes 84 val1 = 98 //above range: loops to becomes 18 i'd like not to resort to using a series of if/else statements, but one would be fine if it's absolutely required. is that even possible?

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  • Step math function

    - by ekapek
    Hi I need function which returns: for any number from range = result [0.001,0.01) => 0.01 [0.01,0.1) => 0.1 [0.1,1) => 1 [1,10) => 10 [10,100) => 100 etc. My first idea was to use if, but this the worst way. Is there a simple solution?

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  • Math Mod Containing Numbers

    - by TheDarkIn1978
    i would like to write a simple line of code, without resorting to if statements, that would evaluate whether a number is within a certain range. i can evaluate from 0 - Max by using the modulus. 30 % 90 = 30 //great however, if the test number is greater than the maximum, using modulus will simply start it at 0 for the remaining, where as i would like to limit it to the maximum if it's past the maximum 94 % 90 = 4 //i would like answer to be 90 it becomes even more complicated, to me anyway, if i introduce a minimum for the range. for example: minimum = 10 maximum = 90 therefore, any number i evaluate should be either within range, or the minimum value if it's below range and the maximum value if it's above range -76 should be 10 2 should be 10 30 should be 30 89 should be 89 98 should be 90 23553 should be 90 is it possible to evaluate this with one line of code without using if statements?

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  • [MATH]Project an axis to a plane

    - by Robert
    how do i project the X axis to a plane if the plane is defined by three points? see pic here: http://129.25.16.135:2080/v6.5/books/usb/graphics/iconventions-local-surfaces.png The default local 1-direction is the projection of the global x-axis onto the surface. If the global x-axis is within 0.1° of being normal to the surface, the local 1-direction is the projection of the global z-axis onto the surface. let's suppose that these points are: t1 = [-0.362879991531372, 0.357021987438202, -0.373737007379532] t2 = [-0.383525013923645, 0.371621012687683, -0.383549988269806] t3 = [-0.383534014225006, 0.34629300236702, -0.38544899225235] is the vector [0.78280971952246, -0.0307519963686645, 0.411184845614438] correct answer in this case? i've calculated the angle between the surf and x (1,0,0) is ~28°. and can you give the entire procedure for the calculation, because i'm just puzzled.

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  • PHP Math issue with negatives [closed]

    - by user1269625
    Possible Duplicate: PHP negatives keep adding I have this code here.... $remaining = 0; foreach($array as $value=>$row){ $remaining = $remaining + $row['remainingbalance']; } What its doing is that it is going through all the remaining balances in the array which are -51.75 and -17.85 with the code above I get -69.60 which is correct. But I am wondering how when its two negatives if they could subtract? Is that possible? I tried this $remaining = 0; foreach($clientArrayInvoice as $value=>$row){ $remaining = $remaining + abs($row['remainingbalance']); } but it gives me 69.60 without the negative. Anyone got any ideas? my goal is to take -51.75 and -17.85 and come up with -33.90 only when its a negative to do subtract. otherwise add

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  • Double-byte characters in querystring using PHP

    - by Jeffrey Berthiaume
    I'm trying to figure out how to create personalized urls for double-byte languages. For example, this url from Amazon Japan has Japanese characters within the querystring (specifically, the path): http://www.amazon.co.jp/????????-DVD-???/dp/B00005R5J3/ref=sr_1_3?ie=UTF8&s=dvd&qid=1269891925&sr=8-3 What I would like to do is have: http://www.mysite.com/???????? or even http://www.mysite.com/index.php?name=???????? be able to properly decode the $GET[name] string. I think I have tried all of the urldecode and utf8_decode possibilities, but I just get gibberish in response. This all works fine in a form $_POST, but I need these urls to be emailable...

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  • ASP.Net double-click problem

    - by David Archer
    Hi there, having a slight problem with an ASP.net page of mine. If a user were to double click on a "submit" button it will write to the database twice (i.e. carry out the 'onclick' method on the imagebutton twice) How can I make it so that if a user clicks on the imagebutton, just the imagebutton is disabled? I've tried: <asp:ImageButton runat="server" ID="VerifyStepContinue" ImageUrl=image src ToolTip="Go" TabIndex="98" CausesValidation="true" OnClick="methodName" OnClientClick="this.disabled = true;" /> But this OnClientClick property completely stops the page from being submitted! Any help? Sorry, yes, I do have Validation controls... hence the icky problem.

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  • string parsing to double fails in C++

    - by helixed
    Here's a fun one I've been trying to figure out. I have the following program: #include <iostream> #include <string> #include <sstream> using namespace std; int main(int argc, char *argv[]) { string s("5"); istringstream stream(s); double theValue; stream >> theValue; cout << theValue << endl; cout << stream.fail(); } The output is: 0 1 I don't understand why this is failing. Could somebody please tell me what I'm doing wrong? Thanks, helixed

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  • Save matrix of double values in OpenCV

    - by Christian
    I have an OpenCV matrix of double (CV_32F) values. I'd like to save it to the disk. I know, I could convert it to an 1-Channel 8-bit IplImage and save it. But that way, I loose precision. Is there a way to save it directly in the 32-bit format, without having to convert it first? It also would be nice, if the resulting file would have an image format, so I can view the result as an image.

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