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  • initial conditions in coupled systems

    - by Alireza
    how should i write the initial conditions and solve two coupled differential equation? for ex. like: s1 := diff(n[D](t), t) = a-b*n[D](t)^2-c*n[D](t)-e*n[D](t)*n[T](t) s2 := diff(n[T](t), t) = b*n[D](t)^2-c*n[D](t)-e*n[D](t)*n[T](t) dsolve({s1, s2});

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  • Function lfit in numerical recipes, providing a test function

    - by Simon Walker
    Hi I am trying to fit collected data to a polynomial equation and I found the lfit function from Numerical Recipes. I only have access to the second edition, so am using that. I have read about the lfit function and its parameters, one of which is a function pointer, given in the documentation as void (*funcs)(float, float [], int)) with the help The user supplies a routine funcs(x,afunc,ma) that returns the ma basis functions evaluated at x = x in the array afunc[1..ma]. I am struggling to understand how this lfit function works. An example function I found is given below: void fpoly(float x, float p[], int np) /*Fitting routine for a polynomial of degree np-1, with coe?cients in the array p[1..np].*/ { int j; p[1]=1.0; for (j=2;j<=np;j++) p[j]=p[j-1]*x; } When I run through the source code for the lfit function in gdb I can see no reference to the funcs pointer. When I try and fit a simple data set with the function, I get the following error message. Numerical Recipes run-time error... gaussj: Singular Matrix ...now exiting to system... Clearly somehow a matrix is getting defined with all zeroes. I am going to involve this function fitting in a large loop so using another language is not really an option. Hence why I am planning on using C/C++. For reference, the test program is given here: int main() { float x[5] = {0., 0., 1., 2., 3.}; float y[5] = {0., 0., 1.2, 3.9, 7.5}; float sig[5] = {1., 1., 1., 1., 1.}; int ndat = 4; int ma = 4; /* parameters in equation */ float a[5] = {1, 1, 1, 0.1, 1.5}; int ia[5] = {1, 1, 1, 1, 1}; float **covar = matrix(1, ma, 1, ma); float chisq = 0; lfit(x,y,sig,ndat,a,ia,ma,covar,&chisq,fpoly); printf("%f\n", chisq); free_matrix(covar, 1, ma, 1, ma); return 0; } Also confusing the issue, all the Numerical Recipes functions are 1 array-indexed so if anyone has corrections to my array declarations let me know also! Cheers

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  • Elliptic Curve Diffie-Hellman

    - by cmaduro
    Does the Elliptic curve diffie hellman calculation look any different from the standard one defined here: /* * The basic Diffie-Hellman Key Agreement Equation * * The client initiates * A = g^a mod p * * Sends (g p A) to the server * * The server calculates B * B = g^b mod p * * Sends B back to client * * The client calculates K * K = B^a mod p * * The server calucaltes K * K = A^b mod p * */ Or is it just a specific way of selecting g, a, p and b? How are g,a,p and b selected anyway?

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  • How does the elliptic-curve version of Diffie-Hellman cryptography work?

    - by cmaduro
    Does the Elliptic curve diffie hellman calculation look any different from the standard one defined here: /* * The basic Diffie-Hellman Key Agreement Equation * * The client initiates * A = g^a mod p * * Sends (g p A) to the server * * The server calculates B * B = g^b mod p * * Sends B back to client * * The client calculates K * K = B^a mod p * * The server calucaltes K * K = A^b mod p * */ Or is it just a specific way of selecting g, a, p and b? How are g,a,p and b selected anyway?

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  • Database time data retrieval, time based queries

    - by Raphael Pineda
    I am new to time manipulation or time arithmetic operations and am currently developing a navigation system with Web server based information and currently I have this Database that contains a table peek hours whose columns are id, start_time, end_time , edge_id, day_of_the_week, edge_weight ------------------------------------------------------------------------ | Peek Hours | ------------------------------------------------------------------------ | | | | | | | | id | start_time | end_time | edge_id | day_of_the_week | edge_weight | | | | | | | | ------------------------------------------------------------------------ I am using PHP as a webservice and so based on the current time i want to get all the records that would fit this equation start_time< current_time < end_time

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  • Setting the origin to center of the screen instead of the top left screen?(iPhone)

    - by thyrgle
    Hi, I am working on an iPhone app and I am trying to make something that has to do with line-circle collision detection. I am using the slope of the line and checking if the coordinates of a circle suffice the equation y = mx + b. But, with the current origin (0,0) at the top left it is a pain to get the slope. Any way I can convert the coordinates so the origin is in the center of the screen?

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  • Calculating rotation and translation matrices between two odometry positions for monocular linear triangulation

    - by user1298891
    Recently I've been trying to implement a system to identify and triangulate the 3D position of an object in a robotic system. The general outline of the process goes as follows: Identify the object using SURF matching, from a set of "training" images to the actual live feed from the camera Move/rotate the robot a certain amount Identify the object using SURF again in this new view Now I have: a set of corresponding 2D points (same object from the two different views), two odometry locations (position + orientation), and camera intrinsics (focal length, principal point, etc.) since it's been calibrated beforehand, so I should be able to create the 2 projection matrices and triangulate using a basic linear triangulation method as in Hartley & Zissermann's book Multiple View Geometry, pg. 312. Solve the AX = 0 equation for each of the corresponding 2D points, then take the average In practice, the triangulation only works when there's almost no change in rotation; if the robot even rotates a slight bit while moving (due to e.g. wheel slippage) then the estimate is way off. This also applies for simulation. Since I can only post two hyperlinks, here's a link to a page with images from the simulation (on the map, the red square is simulated robot position and orientation, and the yellow square is estimated position of the object using linear triangulation.) So you can see that the estimate is thrown way off even by a little rotation, as in Position 2 on that page (that was 15 degrees; if I rotate it any more then the estimate is completely off the map), even in a simulated environment where a perfect calibration matrix is known. In a real environment when I actually move around with the robot, it's worse. There aren't any problems with obtaining point correspondences, nor with actually solving the AX = 0 equation once I compute the A matrix, so I figure it probably has to do with how I'm setting up the two camera projection matrices, specifically how I'm calculating the translation and rotation matrices from the position/orientation info I have relative to the world frame. How I'm doing that right now is: Rotation matrix is composed by creating a 1x3 matrix [0, (change in orientation angle), 0] and then converting that to a 3x3 one using OpenCV's Rodrigues function Translation matrix is composed by rotating the two points (start angle) degrees and then subtracting the final position from the initial position, in order to get the robot's straight and lateral movement relative to its starting orientation Which results in the first projection matrix being K [I | 0] and the second being K [R | T], with R and T calculated as described above. Is there anything I'm doing really wrong here? Or could it possibly be some other problem? Any help would be greatly appreciated.

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  • When to call glEnable(GL_FRAMEBUFFER_SRGB)?

    - by Steven Lu
    I have a rendering system where I draw to an FBO with a multisampled renderbuffer, then blit it to another FBO with a texture in order to resolve the samples in order to read off the texture to perform post-processing shading while drawing to the backbuffer (FBO index 0). Now I'd like to get some correct sRGB output... The problem is the behavior of the program is rather inconsistent between when I run it on OS X and Windows and this also changes depending on the machine: On Windows with the Intel HD 3000 it will not apply the sRGB nonlinearity but on my other machine with a Nvidia GTX 670 it does. On the Intel HD 3000 in OS X it will also apply it. So this probably means that I'm not setting my GL_FRAMEBUFFER_SRGB enable state at the right points in the program. However I can't seem to find any tutorials that actually tell me when I ought to enable it, they only ever mention that it's dead easy and comes at no performance cost. I am currently not loading in any textures so I haven't had a need to deal with linearizing their colors yet. To force the program to not simply spit back out the linear color values, what I have tried is simply comment out my glDisable(GL_FRAMEBUFFER_SRGB) line, which effectively means this setting is enabled for the entire pipeline, and I actually redundantly force it back on every frame. I don't know if this is correct or not. It certainly does apply a nonlinearization to the colors but I can't tell if this is getting applied twice (which would be bad). It could apply the gamma as I render to my first FBO. It could do it when I blit the first FBO to the second FBO. Why not? I've gone so far as to take screen shots of my final frame and compare raw pixel color values to the colors I set them to in the program: I set the input color to RGB(1,2,3) and the output is RGB(13,22,28). That seems like quite a lot of color compression at the low end and leads me to question if the gamma is getting applied multiple times. I have just now gone through the sRGB equation and I can verify that the conversion seems to be only applied once as linear 1/255, 2/255, and 3/255 do indeed map to sRGB 13/255, 22/255, and 28/255 using the equation 1.055*C^(1/2.4)+0.055. Given that the expansion is so large for these low color values it really should be obvious if the sRGB color transform is getting applied more than once. So, I still haven't determined what the right thing to do is. does glEnable(GL_FRAMEBUFFER_SRGB) only apply to the final framebuffer values, in which case I can just set this during my GL init routine and forget about it hereafter?

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  • Convolving two signals

    - by John Elway
    Calculate the convolution of the following signals (your answer will be in the form of an equation): h[n] = delta[n-1] + delta[n+1], x[n] = delta[n-a] + delta[n+b] I'm lost as to what I do with h and x. Do I simply multiply them? h[n]*x[n]? I programmed convolution with several types of blurs and edge detectors, but I don't see how to translate that knowledge to this problem. please help!

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  • drawing circle without floating point calculation

    - by zaharpopov
    This is common interview question (according to some interview sites) but I can find no normal answers in Internet - some are wrong and some point to complex theory I expect not looked for in interview (like Bressenham algorithm). The question is simple: The circle equation is: x^2 + y^2 = R^2. Given R, draw 0,0-centered circle as best as possible without using any floating point (no trigo, square roots, and so on, only integers)

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  • Calculate area under FFT graph in Matlab

    - by lytheone
    Hiya, Currently I did a FFT of a set of data which gives me a plot with frequency at x axis and amplitude at y axis. I would like to calculate out the area under graph to give me energy. I am not sure how to determinate the area because i am without the equation and also i only want a certain area of the plot rather than whole area under the plot. Is there a way i can do it?

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  • RSA PKCS1 implementation in Python

    - by user307016
    I'm working on the RSA PKCS1 implementation in Python,here's the message block i got: m = [0,2,random paddings,0,message integers] I read the RFC2313,and get a equation seems for transforming the message block object into an big-edian integer. I just get confused about how to transform it in Python. Any help would be appreciated.

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  • How would someone implement mathematical formulae in java?

    - by Mohit Deshpande
    What I mean is like have to user input a string with multiple variables and get the value of those variable. Like a simple quadratic formula: x^2 + 5x + 10. Or in java: (Math.pow(x,2)) + (x * 5) + 10The user would then enter that and then the program would solve for x. I will be using the BeanShell Interpreter class to interpret the string as an equation. But how would I solve for x?

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  • Is there a C++ graphing library?

    - by thyrgle
    Is there a C++ graphing library that can display visual graphs (such as hyperbolas and parabolas and linear equations) based on the equation it is given and that is cross platform? Or am I just asking for too much...

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  • Which Cassandra API provides the highest level of abstraction?

    - by knorv
    There are a lot of Cassandra API:s available and usually the programming language preference determines the choice of API. However, if we take the programming language component out of the equation, what Cassandra API provides the highest level of abstraction? Definition of "level of abstraction" in this context: An API providing a lot of extra goodies such as index handling, etc would be considered being at a higher abstraction layer than a bare bones "close to Thrift" API.

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  • multiple figure in latex with captions.

    - by asd
    Hi, How can I insert multiple figures each of them has a caption and label, without using minipage. I wrote this code, but just there is one caption :( \begin{figure}[htp] \centering \label{figur}\caption{equation...} \begin{tabular}{cc} % Requires \usepackage{graphicx} \includegraphics[width=60mm]{explicit3185.eps}& \includegraphics[width=60mm]{explicit3183.eps}\\ \includegraphics[width=60mm]{explicit1501.eps}& \includegraphics[width=60mm]{explicit23185.eps}\\ \includegraphics[width=60mm]{explicit23183.eps}& \includegraphics[width=60mm]{explicit21501.eps}\\ \end{tabular} \end{figure}

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  • AIS is hiring!

    - by Steve Michelotti
    My company, Applied Information Sciences (AIS), is currently hiring for multiple positions. AIS is growing and we have immediate needs for all levels of technologists with a focus developing on the Microsoft stack!  We are seeking .NET developers with a strong Object Oriented Foundation around the DC metro area.  Our goal is to find smart people that are technology enthusiasts and interested in staying on the bleeding edge.  If you have a passion for solving complex business problems by building flexible and scalable solutions, then we want to talk to you!  Our clients are demanding the latest technologies and we have upcoming projects using .NET 4.0, ASP.NET MVC, Silverlight 4, VS2010 with SharePoint 2010.  If you have been exposed to these technologies – great!  If not, then we will train you!  Bottom line…we want smart, capable people with a drive for success! See all of our open positions here. If you’re interested, feel free to send me a private message through my blog here.

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  • How do I make good guy attacks only hit bad guys and vice versa?

    - by tieTYT
    My game has many different type of good guys and many different type of bad guys. They will all be firing projectiles at each other but I don't want any accidental collateral damage to occur for either alignment. So bad guys should not be able to hit/damage other bad guys and good guys should not be able to hit/damage other good guys. The way I'm thinking of solving this is by making it so that the Unit instance (this is javascript, btw), has an alignment property that can be either good or bad. And I'll only let collision happen if the class Attack boolean didAttackCollideWithTarget(target) return attack.source.alignment != target.alignment and collisionDetected(attack.source, target) This is pseudo-code, of course. But I'm asking this question because I get the sense that there might be a much more elegant way to design this besides adding yet another property to my Unit class.

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  • Ubuntu 11.10 cannot boot, gets stuck at BusyBox

    - by Ivan Dokov
    I am using Ubuntu 11.10. An hour ago I had my laptop Sony Vaio VPCEB1S1E running. I saw there are updates to install and I installed them. I turned off the laptop and now when I turn it on it loads until BusyBox v1.18.4 appears. I've seen suggestions for solving this on askubuntu. I booted Puppy Linux from USB and repaired the partition where the Ubuntu is installed. I rebooted but it did not help. I saw other suggestions like writing "exit" at the BusyBox prompt. This didn't help either. I love the Ubuntu OS, but these days I get problems like this while booting. The last times I could repair it with GParted, but then it wasn't a problem with BusyBox, it was some other error, like "cannot boot /". The same problem had occurred on Ubuntu 10.10 and there I had repaired it with GParted.

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  • Bytes by MSDN - Let's talk Cloud

    - by Wallym
    While I was at DevConnections in Las Vegas, I was honored to be interviewed by Tim Huckaby for "Bytes by MSDN" on Cloud Computing. Here's a short intro from the talk:Do you believe in the Cloud? Wallace McClure, Founder and Architect of Scalable Development, Inc., does. His customers are extremely interested in the value and economies of scale that Cloud Computing, and more specifically, Windows Azure can bring. Building out an infrastructure that supports your web service or application can be expensive, complicated and time consuming. Or you could look to the Microsoft cloud. The Windows Azure platform is a flexible cloud–computing platform that lets you focus on solving business problems and addressing customer needs. Wally talks about all this, and more, in this interview with Tim Huckaby, and in his Windows Azure podcasts.

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  • How to familiarize myself with Python

    - by Zel
    I am Python beginner. Started Python 1.5 months back. I downloaded the Python docs and read some part of the tutorial. I have been programming on codechef.com and solving problems of projecteuler. I am thinking of reading Introduction to algorithms and following this course on MIT opencourse ware as I haven't been getting much improvement in programming and I am wasting much time thinking just what should I do when faced with any programming problem. But I think that I still don't know the correct way to learn the language itself. Should I start the library reference or continue with Python tutorial? Is learning algorithms useful for language such as C and not so much for Python as it has "batteries included"? Are there some other resources for familiarization with the language and in general for learning to solve programming problems? Or do I need to just devote some more time?

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  • TechEd 2010 Thanks and Demos

    - by Adam Machanic
    Thank you to everyone who attended my three sessions at this year's TechEd show in New Orleans. I had a great time presenting and answering the really great questions posed by attendees. My sessions were: DAT317 T-SQL Power! The OVER Clause: Your Key to No-Sweat Problem Solving Have you ever stared at a convoluted requirement, unsure of where to begin and how to get there with T-SQL? Have you ever spent three days working on a long and complex query, wondering if there might be a better way? Good...(read more)

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