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Search found 585 results on 24 pages for 'numerical equations'.

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• Framework/tool for processing C++ unit tests with numerical output

  - by David Claridge

  Hi, I am working on a C++ application that uses computer vision techniques to identify various types of objects in a sequence of images. The (1000+) images have been hand-classified, so we have an XML file for each image containing a description of where the objects are actually located in the images. I would like to know if there is a testing framework that can understand/graph results from tests that are numeric, in this case some measure of the error in the program's classification of the images, rather than just pass/fail style unit tests. We would like to use something like CDash/CTest for running these automated tests, and viewing over time how improvements to the vision algorithms are causing the images to be more correctly classified. Does anyone know of a tool/framework that can do this?

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• Django: ordering numerical value with order_by

  - by h3

  I'm in a situation where I must output a quite large list of objects by a CharField used to store street addresses. My problem is, that obviously the data is ordered by ASCII codes since it's a Charfield, with the predictable results .. it sort the numbers like this; 1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 2, 20, 21.... Now the obvious step would be to change the Charfield the proper field type (IntegerField let's say), however it cannot work since some address might have apartments .. like "128A". I really don't know how I can order this properly ..

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• str_replace between two numerical strings

  - by user330840

  Another problem with str_replace, I would like to change the following $title data into URL by taking the $string between number in the beginning and after dash (-) Chicago's Public Schools - $10.3M New Jersey - $3M Michigan: Public Health - $1M The desire output is: chicago-public-school new-jersey michigan-public-health PHP code I am using $title = ucwords(strtolower(strip_tags(str_replace("1: ","",$title)))); $x=1; while($x <= 10) { $title = ucwords(strtolower(strip_tags(str_replace("$x: ","",$title)))); $x++; } $link = preg_replace('/[<>()!#?:.$%\^&=+~`*&#233;"\']/', '',$title); $money = str_replace(" ","-",$link); $link = explode(" - ",$link); $link = preg_replace(" (\(.*?\))", "", $link[0]); $amount = preg_replace(" (\(.*?\))", "", $link[1]); $code_entities_match = array( '&#39;s' ,'&quot;' ,'!' ,'@' ,'#' ,'$' ,'%' ,'^' ,'&' ,'*' ,'(' ,')' ,'+' ,'{' ,'}' ,'|' ,':' ,'"' ,'<' ,'>' ,'?' ,'[' ,']' ,'' ,';' ,"'" ,',' ,'.' ,'_' ,'/' ,'*' ,'+' ,'~' ,'`' ,'=' ,' ' ,'---' ,'--','--'); $code_entities_replace = array('' ,'-' ,'-' ,'' ,'' ,'' ,'-' ,'-' ,'' ,'' ,'' ,'' ,'' ,'' ,'' ,'-' ,'' ,'' ,'' ,'' ,'' ,'' ,'' ,'' ,'' ,'-' ,'' ,'-' ,'-' ,'' ,'' ,'' ,'' ,'' ,'-' ,'-' ,'-','-'); $link = str_replace($code_entities_match, $code_entities_replace, $link); $link = strtolower($link); Unfortunately the result I got: -chicagoamp9s-public-school 2-new-jersey 3-michigan-public-health Anyone has a better solution for this? Thanks guys! (the &#39; changed into amp9 - wonder why?)

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• Convert complex numerical array to associative array [PHP]

  - by user1500412

  I have an array data that look like this : Array ( [0] => Array ( [0] => Name: [1] => John W. [2] => Registration ID: [3] => 36 ) [1] => Array ( [0] =>Age: [1] => 35 [2] => Height: [3] => 5'11" ) [3] => Array ( [0] => Sex: [1] => M [2] => Weight: [3] => 200lbs ) [4] => Array ( [0] => Address ) [5] => Array ( [0] => 6824 crestwood dr delphi, IN 46923 )) And I want to convert it to associative array like this : Array( ['Name']=> John W. ['Registration ID']=> 36 ['Age']=> 35 ['Height'] => 5'11'' ['Sex']=>M ['Weight']=>200lbs ['Address']=>6824 crestwood dr delphi, IN 46923 ) I have no idea at all how to do this, since the supposed to be array column header were also in sequence, so it makes difficult to convert this array. Any help I appreciate, thx.

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• Error in Ordinary Differential Equation representation

  - by Priya M

  UPDATE I am trying to find the Lyapunov Exponents given in link LE. I am trying to figure it out and understand it by taking the following eqs for my case. These are a set of ordinary differential equations (these are just for testing how to work with cos and sin as ODE) f(1)=ALPHA*(y-x); f(2)=x*(R-z)-y; f(3) = 10*cos(x); and x=X(1); y=X(2); cos(y)=X(3); f1 means dx/dt;f2 dy/dt and f3 in this case would be -10sinx. However,when expressing as x=X(1);y=X(2);i am unsure how to express for cos.This is just a trial example i was doing so as to know how to work with equations where we have a cos,sin etc terms as a function of another variable. When using ode45 to solve these Eqs [T,Res]=sol(3,@test_eq,@ode45,0,0.01,20,[7 2 100 ],10); it throws the following error ??? Attempted to access (2); index must be a positive integer or logical. Error in ==> Eq at 19 x=X(1); y=X(2); cos(x)=X(3); Is my representation x=X(1); y=X(2); cos(y)=X(3); alright? How to resolve the error? Thank you

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• Why can't flowcharts or mathematical equations created in Microsoft Office and saved in .docx format be opened by LibreOffice?

  - by user33831

  I am using Ubuntu 11.10 and LibreOffice that comes with it. Before this , I was a Windows user and some of my previous documents were saved in .docx format. I tried to use LibreOffice to open those .docx file and I can view all text, however I can't view the flowchart I drew and also mathematical equations. Another issue is, if I create new flowchart with LibreOffice and save it in .docx file, when I re-open that file, I can't view those flowcharts, but those flowcharts are there, occupied space. No problem for .odt format of course. Does anyone know why this happens? Thanks in advanced.

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• Lisp, OCaml or what for Runge Kutta?

  - by Eelvex

  Which language would you propose for solving a system with: first order differential equations complex variables N-dimensions using 4th order Runge Kutta or the like. Speed matters a lot but would sacrifice for: Elegant (clean and short) code Flexibility + scalability I'm mostly between a Lisp and OCaml but any other suggestion is welcomed. Thanks!

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• Using logarithms to normalize a vector to avoid overflow

  - by muscicapa

  http://stackoverflow.com/questions/2293762/problem-with-arithmetic-using-logarithms-to-avoid-numerical-underflow-take-2 Having seen the above and having seen softmax normalization I was trying to normalize a vector while avoiding overflow - that is (x1 x2 x3 x4 ... xn) the normalized form for me has the sum of squares as 1.0 So what I thought of doing is s=(2*log(x1)+2*log(x2)+...+2*log(xn))/2 so the two factor can be taken off and finally the normalized vector is exp(log(x1)-s), , ..., exp(log(xn)-s) but I am evidently doing something wrong here, what?

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• C or Ada for engineering computations?

  - by yCalleecharan

  Hi,as an engineer I currently use C to write programs dealing with numerical methods. I like C as it's very fast. I don't want to move to C++ and I have been reading a bit about Ada which has some very good sides. I believe that much of the software in big industries have been or more correctly were written in Ada. I would like to know how C compares with Ada. Is Ada fast as C? I understand that no language is perfect but I would like to know if Ada was designed for scientific computing. Thanks a lot...

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• Efficiency of manually written loops vs operator overloads (C++)

  - by Sagekilla

  Hi all, in the program I'm working on I have 3-element arrays, which I use as mathematical vectors for all intents and purposes. Through the course of writing my code, I was tempted to just roll my own Vector class with simple +, -, *, /, etc overloads so I can simplify statements like: for (int i = 0; i < 3; i++) r[i] = r1[i] - r2[i]; // becomes: r = r1 - r2; Which should be more or less identical in generated code. But when it comes to more complicated things, could this really impact my performance heavily? One example that I have in my code is this: Manually written version: for (int j = 0; j < 3; j++) { p.vel[j] = p.oldVel[j] + (p.oldAcc[j] + p.acc[j]) * dt2 + (p.oldJerk[j] - p.jerk[j]) * dt12; p.pos[j] = p.oldPos[j] + (p.oldVel[j] + p.vel[j]) * dt2 + (p.oldAcc[j] - p.acc[j]) * dt12; } Using a Vector class with operator overloads: p.vel = p.oldVel + (p.oldAcc + p.acc) * dt2 + (p.oldJerk - p.jerk) * dt12; p.pos = p.oldPos + (p.oldVel + p.vel) * dt2 + (p.oldAcc - p.acc) * dt12; I am compiling my code for maximum possible speed, as it's extremely important that this code runs quickly and calculates accurately. So will me relying on my Vector's for these sorts of things really affect me? For those curious, this is part of some numerical integration code which is not trivial to run in my program. Any insight would be appreciated, as would any idioms or tricks I'm unaware of.

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• How should I deal with floating numbers that numbers that can get so small that the become zero

  - by Tristan Havelick

  So I just fixed an interesting bug in the following code, but I'm not sure the approach I took it the best: p = 1 probabilities = [ ... ] # a (possibly) long list of numbers between 0 and 1 for wp in probabilities: if (wp > 0): p *= wp # Take the natural log, this crashes when 'probabilites' is long enough that p ends up # being zero try: result = math.log(p) Because the result doesn't need to be exact, I solved this by simply keeping the smallest non-zero value, and using that if p ever becomes 0. p = 1 probabilities = [ ... ] # a long list of numbers between 0 and 1 for wp in probabilities: if (wp > 0): old_p = p p *= wp if p == 0: # we've gotten so small, its just 0, so go back to the smallest # non-zero we had p = old_p break # Take the natural log, this crashes when 'probabilites' is long enough that p ends up # being zero try: result = math.log(p) This works, but it seems a bit kludgy to me. I don't do a ton of this kind of numerical programming, and I'm not sure if this is the kind of fix people use, or if there is something better I can go for.

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• Latex --- Is there a way to shift the equation numbering one tab space from the right margin (shift

  - by Murari

  I have been formatting my dissertation and one little problem is stucking me up. I used the following code to typeset an equation \begin{align} & R=\frac{P^2}{P+S'} \label{eqn:SCS}\\ &\mbox {where} \quad \mbox R = \mbox {Watershed Runoff} \notag\\ &\hspace{0.63in} \mbox P = \mbox{Rainfall} \notag\\ &\hspace{0.63in} \mbox S' = \mbox{Storage in the watershed $=\frac{1000}{CN}-10$ }\notag \end{align} My output requirement is such that: The equation should begin one tab space from the left margin The equation number should end at one tab space from the right margin With the above code, I have the equation begin at the right place but not the numbering. Any help will be extremely appreciated. Thanks MP

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• What's the fastest way to approximate the period of data using Octave?

  - by John

  I have a set of data that is periodic (but not sinusoidal). I have a set of time values in one vector and a set of amplitudes in a second vector. I'd like to quickly approximate the period of the function. Any suggestions? Specifically, here's my current code. I'd like to approximate the period of the vector x(:,2) against the vector t. Ultimately, I'd like to do this for lots of initial conditions and calculate the period of each and plot the result. function xdot = f (x,t) xdot(1) =x(2); xdot(2) =-sin(x(1)); endfunction x0=[1;1.75]; #eventually, I'd like to try lots of values for x0(2) t = linspace (0, 50, 200); x = lsode ("f", x0, t) plot(x(:,1),x(:,2)); Thank you! John

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• Matlab help: I am given a second order differential equation.I need to use matlab to find unit step response and impulse response?

  - by Cady Smith

  I have the second order differential equation d^2(y(t))/dt^2+ B1*d(y(t))/dt+ c1*y(t)=A1*x(t) t is in seconds and is greater than 0. A1, B1, C1 are constants that equal: A1= 3.8469x10^6 B1= 325.6907 C1= 3.8469x10^6 This system is linear, time-invariant, and casual. The system is called H1. I want to use Matlab to compute and plot the impulse response function h1(t) and the unit step response function g1(t) of this system.

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• Is there a way to shift the equation numbering one tab space from the right margin (shift towards le

  - by Murari

  I have been formatting my dissertation and one little problem is stucking me up. I used the following code to typeset an equation \begin{align} & R=\frac{P^2}{P+S'} \label{eqn:SCS}\\ &\mbox {where} \quad \mbox R = \mbox {Watershed Runoff} \notag\\ &\hspace{0.63in} \mbox P = \mbox{Rainfall} \notag\\ &\hspace{0.63in} \mbox S' = \mbox{Storage in the watershed $=\frac{1000}{CN}-10$ }\notag \end{align} My output requirement is such that: The equation should begin one tab space from the left margin The equation number should end at one tab space from the right margin With the above code, I have the equation begin at the right place but not the numbering. Any help will be extremely appreciated. Thanks MP

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• How to type all the math, stat, greek, equations EFFICIENTLY in libreoffice?

  - by kernel_panic

  i am preparing a report related to physics which is full of greek, stat and calculus things, i know there is this question how to insert a greek symbol, but my problem is i cant fiddle with a drop down/ scroll list for for every symbol(my paper in FULL of those), is there a way to do something with my keyboard layout, and turn it into something like the one Tony Stark uses in Ironman(i am not kidding please). i am literally tired for this fiddle-work for half of the day and have completed just 2 sheets, hmmm.

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• Force apt-get to ask all install equations again?

  - by user204744

  I made a mistake. I answered the wrong way when installing something with apt-get. Now, when I purge it and reinstall it, it doesn't ask me the question any more. How do I force apt-get to ask me the question again? I'd really rather do this through the package manager than making the changes manually; that's the whole point of using a package manager.... The package in question is jackd. The first time I installed it, I answered "no" to the question about real-time priority. Now, I wish I'd said yes. However, even though I purge and install it again, I don't get the question. (I have tried dpkg-reconfigure jackd -- that doesn't give me any questions to answer.)

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• Using Taylor Series to Avoid Loss of Precision

  - by Zachary

  I'm trying to use Taylor series to develop a numerically sound algorithm for solving a function. I've been at it for quite a while, but haven't had any luck yet. I'm not sure what I'm doing wrong. The function is f(x)=1 + x - sin(x)/ln(1+x) x~0 Also: why does loss of precision even occur in this function? when x is close to zero, sin(x)/ln(1+x) isn't even close to being the same number as x. I don't see where significance is even being lost. In order to solve this, I believe that I will need to use the Taylor expansions for sin(x) and ln(1+x), which are x - x^3/3! + x^5/5! - x^7/7! + ... and x - x^2/2 + x^3/3 - x^4/4 + ... respectfully. I have attempted to use like denominators to combine the x and sin(x)/ln(1+x) components, and even to combine all three, but nothing seems to work out correctly in the end. Any help is appreciated.

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• Open source alternative to MATLAB's fmincon function?

  - by dF

  Is there an open-source alternative to MATLAB's fmincon function for constrained linear optimization? I'm rewriting a MATLAB program to use Python / NumPy / SciPy and this is the only function I haven't found an equivalent to. A NumPy-based solution would be ideal, but any language will do.

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• Diagonalization of bidiagonal matrix with QR

  - by Simon

  How can i diagonalize the matrix A having the orthogonal transformations P and Q: A = Q*B*P ? I saw something pointing out to QR transformations, but i couldn't find out the algorithm.

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• How to find a binary logarithm very fast? (O(1) at best)

  - by psihodelia

  Is there any very fast method to find a binary logarithm of an integer number? For example, given a number x=52656145834278593348959013841835216159447547700274555627155488768 such algorithm must find y=log(x,2) which is 215. x is always a power of 2. The problem seems to be really simple. All what is required is to find the position of the most significant 1 bit. There is a well-known method FloorLog, but it is not very fast especially for the very long multi-words integers. What is the fastest method?

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• What ever happened to APL?

  - by lkessler

  When I was at University 30 years ago, I used a programming language called APL. I believe the acronym stood for "A Programming Language", This language was interpretive and was especially useful for array and matrix operations with powerful operators and library functions to help with that. Did you use APL? Is this language still in use anywhere? Is it still available, either commercially or open source? I remember the combinatorics assignment we had. It was complex. It took a week of work for people to program it in PL/1 and those programs ranged from 500 to 1000 lines long. I wrote it in APL in under an hour. I left it at 10 lines for readability, although I should have been a purist and worked another hour to get it into 1 line. The PL/1 programs took 1 or 2 minutes to run on the IBM mainframe and solve the problem. The computer charge was $20. My APL program took 2 hours to run and the charge was $1,500 which was paid for by our Computer Science Department's budget. That's when I realized that a week of my time is worth way more than saving some $'s in someone else's budget. I got an A+ in the course. p.s. Don't miss this presentation entitled: "APL one of the greatest programming languages ever"

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• Matlab-Bisection-Newton-Secant , finding roots?

  - by i z

  Hello and thanks in advance for your possible help ! Here's my problem: I have 2 functions f1(x)=14.*x*exp(x-2)-12.*exp(x-2)-7.*x.^3+20.*x.^2-26.*x+12 f2(x)=54.*x.^6+45.*x.^5-102.*x.^4-69.*x.^3+35.*x.^2+16.*x-4 Make the graph for those 2, the first one in [0,3] and the 2nd one in [-2,2]. Find the 3 roots with accuracy of 6 decimal digits using a) bisection ,b) newton,c)secant.For each root find the number of iterations that have been made. For Newton-Raphson, find which roots have quadratic congruence and which don't. What is the main common thing that roots with no quadratic congruence (Newton's method)? Why ? Excuse me if i ask silly things, but i'm asked to do this with no Matlab courses and I'm trying to learn it myself. There are many issues i have with this exercise . Questions : 1.I only see 2 roots in the graph for the f1 function and 4-5 (?) roots for the function f2 and not 3 roots as the exercise says. Here's the 2 graphs : http://postimage.org/image/cltihi9kh/ http://postimage.org/image/gsn4sg97f/ Am i wrong ? Do both have only 3 roots in [0,3] and [-2,2] ? Concerning the Newton's method , how am i supposed to check out which roots have quadratic congruence and which not??? Accuracy means tolerance e=10^(-6), right ?

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• efficiently determining if a polynomial has a root in the interval [0,T]

  - by user168715

  I have polynomials of nontrivial degree (4+) and need to robustly and efficiently determine whether or not they have a root in the interval [0,T]. The precise location or number of roots don't concern me, I just need to know if there is at least one. Right now I'm using interval arithmetic as a quick check to see if I can prove that no roots can exist. If I can't, I'm using Jenkins-Traub to solve for all of the polynomial roots. This is obviously inefficient since it's checking for all real roots and finding their exact positions, information I don't end up needing. Is there a standard algorithm I should be using? If not, are there any other efficient checks I could do before doing a full Jenkins-Traub solve for all roots? For example, one optimization I could do is to check if my polynomial f(t) has the same sign at 0 and T. If not, there is obviously a root in the interval. If so, I can solve for the roots of f'(t) and evaluate f at all roots of f' in the interval [0,T]. f(t) has no root in that interval if and only if all of these evaluations have the same sign as f(0) and f(T). This reduces the degree of the polynomial I have to root-find by one. Not a huge optimization, but perhaps better than nothing.

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• Lack of IsNumeric function in C#

  - by Michael Kniskern

  One thing that has bothered me about C# since its release was the lack of a generic IsNumeric function. I know it is difficult to generate a one-stop solution to detrmine if a value is numeric. I have used the following solution in the past, but it is not the best practice because I am generating an exception to determine if the value is IsNumeric: public bool IsNumeric(string input) { try { int.Parse(input); return true; } catch { return false; } } Is this still the best way to approach this problem or is there a more efficient way to determine if a value is numeric in C#?

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