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• Inverse Logistic Function / Reverse Sigmoid Function

  - by Chanq

  I am currently coding up a fuzzy logic library in java. I have found the equations for all the standard functions - Grade, inverseGrade, Triangle, Trapezoid, Gaussian. However, I can't find the inverse of the sigmoid/ logistic function. The way I have written the logistic function is java is : //f(x) = 1/(1+e(-x)) public double logistic(double x){ return (1/(1+(Math.exp(-x))); } But I can't work out or find the inverse anywhere. My algebraic/calculus abilities are fairly limited, hence why I haven't been able to work out the inverse of the function. Any hints or pointers would be a big help. Thanks

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• Matlab: how do I force ode45 to take steps of exactly 0.01 on the T axis?

  - by Gravitas

  I'm using Matlab to solve a differential equation. I want to force ode45 to take constant steps, so it always increments 0.01 on the T axis while solving the equation. How do I do this? ode45 is consistently taking optimized, random steps, and I can't seem to work out how to make it take consistent, small steps of 0.01. Here is the code: options= odeset('Reltol',0.001,'Stats','on'); %figure(1); %clf; init=[xo yo zo]'; tspan=[to tf]; %tspan = t0:0.01:tf; [T,Y]=ode45(name,tspan,init,options);

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• Deploying Excel 2003 VSTO Workbook using Sharepoint for versioning control

  - by KClough

  I have an excel 2003 vsto workbook that I would like to make available via sharepoint for version control. Ideally it could be checked in/out by non-developers for tweaking excel equations, and I would be able to deploy the compiled dlls somewhere else when I need to update the managed VSTO code. I understand I may need to use some clickonce functionality as well so when a user first views the sheet they get all the necessary full-trust permissioning. Also, it is my understanding that for a user to use the vsto functionality in an excel 2003 vsto workbook, they must have the compiled dll in thier GAC, is this true? When testing I get trust exceptions otherwise.

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• Graphing a line and scatter points using Matplotlib?

  - by Patrick O'Doherty

  Hi guys I'm using matplotlib at the moment to try and visualise some data I am working on. I'm trying to plot around 6500 points and the line y = x on the same graph but am having some trouble in doing so. I can only seem to get the points to render and not the line itself. I know matplotlib doesn't plot equations as such rather just a set of points so I'm trying to use and identical set of points for x and y co-ordinates to produce the line. The following is my code from matplotlib import pyplot import numpy from pymongo import * class Store(object): """docstring for Store""" def __init__(self): super(Store, self).__init__() c = Connection() ucd = c.ucd self.tweets = ucd.tweets def fetch(self): x = [] y = [] for t in self.tweets.find(): x.append(t['positive']) y.append(t['negative']) return [x,y] if __name__ == '__main__': c = Store() array = c.fetch() t = numpy.arange(0., 0.03, 1) pyplot.plot(array[0], array[1], 'ro', t, t, 'b--') pyplot.show() Any suggestions would be appreciated, Patrick

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• Make UILabel show "No results" instead of "nan"

  - by Mike Rychev

  I have a small app, where user can make some calculations and solve equations. For example, if in a square equation discriminant is less than zero, the x1 and x2 values are "nan", so when I assign x1 and x2 values to UILabels they show "nan" as well. Writing a lot of if's like if(D<0) [label setText:[NSString stringWithFormat: @"No solutions"]]; Doesn't help-there are too many cases. I want to check if after [label setText:[NSString stringWithFormat: @"%f", x]]; label's value is "nan", the label's value will be set to @"No solutions". Doing simple if(label==@"nan") { //code } doesn't help. Thanks in advance!

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• how to apply Discrete wavelet transform on image

  - by abuasis

  I am implementing an android application that will verify signature images , decided to go with the Discrete wavelet transform method (symmlet-8) the method requires to apply the discrete wavelet transform and separate the image using low-pass and high-pass filter and retrieve the wavelet transform coefficients. the equations show notations that I cant understand thus can't do the math easily , also didn't know how to apply low-pass and high-pass filters to my x and y points. is there any tutorial that shows you how to apply the discrete wavelet transform to my image easily that breaks it out in numbers? thanks alot in advance.

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• How can I write a Template.pm filter to generate PNG output from LaTeX source code?

  - by Sinan Ünür

  I am looking for a way of generating PNG images of equations from LATEX source code embedded in templates. For example, given: [% FILTER latex_display ] \begin{eqnarray*} \max && U(x,y) \\ \mathrm{s.t.} && p_x x + p_y y \leq I \\ && x \geq 0, y \geq 0 \end{eqnarray*} [% END %] I would like to get the output: <div class="latex display"><img src="equation.png" width="x" height="y"></div> which should ultimately display as: I am using ttree to generate documents offline. I know about Template::Plugin::Latex but that is geared towards producing actual documents out of LATEX templates. Any suggestions?

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• How to overcome an apparent REST vs. DRY dilemma in rails?

  - by Chris

  A rails app I'm working on features examples of quadratic equations. Obviously, these are all of a common structure: ax^2 + bx + c = 0. I don't want to store every single example of these. I'd rather generate them from a template. Storing hundreds of possible versions of this structure seems highly wasteful and un-DRY. On the other hand, if I generate them, I can't access them again reliably as I could if they were simply multiple database objects. I'm sure there must be a way to overcome this, but I'm still learning rails and I'm obviously not grasping something here. Thanks.

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• What is the best Java numerical method package?

  - by Bob Cross

  I am looking for a Java-based numerical method package that provides functionality including: Solving systems of equations using different numerical analysis algorithms. Matrix methods (e.g., inversion). Spline approximations. Probability distributions and statistical methods. In this case, "best" is defined as a package with a mature and usable API, solid performance and numerical accuracy. Edit: derick van brought up a good point in that cost is a factor. I am heavily biased in favor of free packages but others may have a different emphasis.

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• Fastest way to compress a database or .bak file and transfer it

  - by Nai

  As per the question title. I wonder if there are special programmes or commands that makes zipping up a .bak file and transferring it super quick. I read abour xp_cmdshell here but I'm not sure about the speed. My .bak file is about 12 gigs at the moment. Related to this is the possibility of using Red Gate's SQL Data Compare to just transfer the differential data across the network pipeline but I have never used SQL Data Compare before and I'm not sure how it goes about doing INSERTS on tables with Primary Keys and such. Also, not sure about the speed. Does anyone have any experience with this programme or similar programmes? Cheers!

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• multidimensional vector rotation and angle computation -- how?

  - by macias

  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 2d and 3d this is quite easy, but for more dimensions I am lost, I didn't find anything on google, and I prefer using some already proved&tested equations (avoiding errors introduced by my calculations :-D). Thank you in advance for tips, links, etc. Edit: dimension of the space is the same as dimension of the vectors.

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• Explain a block of crazy JS code inside Sizzle(the CSS selector engine)

  - by Andy Li

  So, here is the function for pre-filtering "CHILD": function(match){ if ( match[1] === "nth" ) { // parse equations like 'even', 'odd', '5', '2n', '3n+2', '4n-1', '-n+6' var test = /(-?)(\d*)n((?:\+|-)?\d*)/.exec( match[2] === "even" && "2n" || match[2] === "odd" && "2n+1" || !/\D/.test( match[2] ) && "0n+" + match[2] || match[2]); // calculate the numbers (first)n+(last) including if they are negative match[2] = (test[1] + (test[2] || 1)) - 0; match[3] = test[3] - 0; } // TODO: Move to normal caching system match[0] = done++; return match; } The code is extracted from line 442-458 of sizzle.js. So, why is the line var test = ..., have the exec inputing a boolean? Or is that really a string? Can someone explain it by splitting it into a few more lines of code?

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• programming question about numbers

  - by Syom

  it's a task, on which i think during whole day. i have four integer numbers a, b, c, d, and ineger x[1,40]. i must write a program, which can find the values of {a,b,c,d}, for which one of following equations is true for any (x<=40, x=1) x=a or x=b or x=a+b or x=a+b+c+d or x+a=c+d or x+a+b=c+d or ... x+a+b+c=d or ... it is very difficult to explain what i want to say. maybe the example will be helpful. example: if x=17, by {a=1,b=2,c=5,d=15} i can write x+a+b=c+d whole question is to present any x[1,40] by {a,b,c,d}. hope that you understand what i want to say, and thanks in advance

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• Expert system for writing programs?

  - by aaa

  I am brainstorming an idea of developing a high level software to manipulate matrix algebra equations, tensor manipulations to be exact, to produce optimized C++ code using several criteria such as sizes of dimensions, available memory on the system, etc. Something which is similar in spirit to tensor contraction engine, TCE, but specifically oriented towards producing optimized rather than general code. The end result desired is software which is expert in producing parallel program in my domain. Does this sort of development fall on the category of expert systems? What other projects out there work in the same area of producing code given the constraints?

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• Preallocate memory for a program in Linux before it gets started

  - by Fyg

  Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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• Interpolating height for a point inside a grid based on a discrete height function.

  - by fastrack20

  Hi, I have been wracking my brain to come up with a solution to this problem. I have a lookup table that returns height values for various points (x,z) on the grid. For instance I can calculate the height at A, B, C and D in Figure 1. However, I am looking for a way to interpolate the height at P (which has a known (x,z)). The lookup table only has values at the grid intervals, and P lies between these intervals. I am trying to calculate values s and t such that: A'(s) = A + s(C-A) B'(t) = B + t(P-B) I would then use the these two equations to find the intersection point of B'(t) with A'(s) to find a point X on the line A-C. With this I can calculate the height at this point X and with that the height at point P. My issue lies in calculating the values for s and t. Any help would be greatly appreciated.

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• Solving linear system over integers with numpy

  - by A. R. S.

  I'm trying to solve an overdetermined linear system of equations with numpy. Currently, I'm doing something like this (as a simple example): a = np.array([[1,0], [0,1], [-1,1]]) b = np.array([1,1,0]) print np.linalg.lstsq(a,b)[0] [ 1. 1.] This works, but uses floats. Is there any way to solve the system over integers only? I've tried something along the lines of print map(int, np.linalg.lstsq(a,b)[0]) [0, 1] in order to convert the solution to an array of ints, expecting [1, 1], but clearly I'm missing something. Could anyone point me in the right direction?

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• Calculating the null space of a matrix

  - by Ainsworth

  I'm attempting to solve a set of equations of the form Ax = 0. A is known 6x6 matrix and I've written the below code using SVD to get the vector x which works to a certain extent. The answer is approximately correct but not good enough to be useful to me, how can I improve the precision of the calculation? Lowering eps below 1.e-4 causes the function to fail. from numpy.linalg import * from numpy import * A = matrix([[0.624010149127497 ,0.020915658603923 ,0.838082638087629 ,62.0778180312547 ,-0.336 ,0], [0.669649399820597 ,0.344105317421833 ,0.0543868015800246 ,49.0194290212841 ,-0.267 ,0], [0.473153758252885 ,0.366893577716959 ,0.924972565581684 ,186.071352614705 ,-1 ,0], [0.0759305208803158 ,0.356365401030535 ,0.126682113674883 ,175.292109352674 ,0 ,-5.201], [0.91160934274653 ,0.32447818779582 ,0.741382053883291 ,0.11536775372698 ,0 ,-0.034], [0.480860406786873 ,0.903499596111067 ,0.542581424762866 ,32.782593418975 ,0 ,-1]]) def null(A, eps=1e-3): u,s,vh = svd(A,full_matrices=1,compute_uv=1) null_space = compress(s <= eps, vh, axis=0) return null_space.T NS = null(A) print "Null space equals ",NS,"\n" print dot(A,NS)

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• 2D pixel array rotation and scaling

  - by Betamoo

  Hi I am working on C# program to process images ( given as int[,] ).. So I have 2D array of pixels, and I need to rotate them around a point, then scale them down to fit the original array.. I already found articles about using matrix to transform to a point and rotate then transform back.. What remains is to scale the resultant image to fit an array of original size.. How that can be done? (preferably with 2 equations one for x and one for y ) Thanks in advance

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• Issue using Python to solve the Coin problem [closed]

  - by challarao

  I'm attempting to solve a problem commonly known as the Coin problem, but using McNuggets. McNuggets come in boxes containing either 6, 9, or 20 nuggets. I want to write a python script that uses Diophantine equations to determine if a given number of McNuggets n can be exactly purchased in these groupings. For example: 26 McNuggets -- Possible: 1 6-pack, 0 9-packs, 1 20-pack 27 McNuggets -- Possible: 0 6-packs, 3 9-packs, 0 20-packs 28 McNuggets -- Not possible This is my current attempt at writing the solution in Python, but the output is incorrect and I'm not sure what's wrong. n=input("Enter the no.of McNuggets:") a,b,c=0,0,0 count=0 for a in range(n): if 6*a+9*b+20*c==n: count=count+1 break else: for b in range(n): if 6*a+9*b+20*c==n: count=count+1 break else: for c in range(n): if 6*a+9*b+20*c==n: count=count+1 break if count>0: print "It is possible to buy exactly",n,"packs of McNuggetss",a,b,c else: print "It is not possible to buy"

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• How to convert string to integer?

  - by user1260584

  So I'm having a hard time with my situation and need some advice. I'm trying to convert my two Strings that I have into integers, so that I can use them in math equations. Here is what I tried, however it brings me an error in the app. ' equals.setOnClickListener(new View.OnClickListener() { public void onClick(View arg0) { // TODO Auto-generated method stub num1 = edit.getText().toString(); num2 = edit.getText().toString(); int first = Integer.parseInt(num1); int second = Integer.parseInt(num2); edit.setText(first + second); } }); Is there something that I am doing wrong? Thank you for any help. EDIT: Yes this is Java. num1 and num2 are strings that I have previously named. What do you mean by trim?

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• Finally, I have my HP 6910p laptop running with 8Gb RAM

  - by Liam Westley

  Today, I received two Corsair Value Select 4Gb DDR SO-DIMMs (from overclock.co.uk) for my aging HP 6910p to give it the extra lease of life to keep it going until the end of 2010.  And here is the proof that Windows 7 64-bit happily sees all 8Gb, There are no 4Gb modules are officially supported for the HP 6910p (they didn’t exist when it was first build).  I was taking a bit of a gamble, and relying on the UK distance selling regulations which meant that even if they didn’t work I’d be able to send them back, getting a full refund and only paying for the return postage. I’d read Keith Comb’s blog back in 2008, (http://blogs.technet.com/b/keithcombs/archive/2008/07/05/loading-a-hp-6910p-with-8gb-of-ram.aspx) where he mentioned ‘trying’ out 4Gb samples of SO-DIMMs in a HP 6910p laptop, but there still appears to be no mentions of running this configuration in any other blog. Seeing how the 8Gb of memory is used is made easier with the new Resource Monitor available in Windows 7.  With two copies of Visual Studio 2008, Outlook, Firefox (with 30+ tabs), TweetDeck (an infamous memory hog) and VMWare workstation running a virtual machine allocated with 2Gb of memory, you might have no ‘free’ memory remaining, but the standby memory is an awesome 2.4Gb, and once the VM is up and running the Hard Faults/sec hovers around zero,   It’s the page fault figure which really counts, because reducing that value means that you are preventing the Windows 7 system drive from being used for virtual memory paging operations.  Even after only a few hours of use it’s noticeable that disc access has been reduced and applications feel more responsive and ‘snappy’.  I did consider the option of purchasing an SSD to replace the main drive, rather than go for 8Gb of RAM, but I think I’ve probably made the correct decision. Given my hobby topic of virtualisation, I take the view that you can never have too much memory.   It was also a decision made easier by the price differential between 8Gb of RAM compared to a decent size SSD.  In the 18 months since Keith Comb tested the first 4Gb SO-DIMMS they have plummeted in price, at just under £100 per 4Gb, they are around a fifth of the price when launched. So if you ever wondered if a HP 6910p can handle 8Gb, now you know.

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• Difference between the terms Material & Effect

  - by codey

  I'm making an effect system right now (I think, because it may be a material system... or both!). The effects system follows the common (e.g. COLLADA, DirectX) effect framework abstraction of Effects have Techniques, Techniques have Passes, Passes have States & Shader Programs. An effect, according to COLLADA, defines the equations necessary for the visual appearance of geometry and screen-space image processing. Keeping with the abstraction, effects contain techniques. Each effect can contain one or many techniques (i.e. ways to generate the effect), each of which describes a different method for rendering that effect. The technique could be relate to quality (e.g. high precision, high LOD, etc.), or in-game-situation (e.g. night/day, power-up-mode, etc.). Techniques hold a description of the textures, samplers, shaders, parameters, & passes necessary for rendering this effect using one method. Some algorithms require several passes to render the effect. Pipeline descriptions are broken into an ordered collection of Pass objects. A pass provides a static declaration of all the render states, shaders, & settings for "one rendering pipeline" (i.e. one pass). Meshes usually contain a series of materials that define the model. According to the COLLADA spec (again), a material instantiates an effect, fills its parameters with values, & selects a technique. But I see material defined differently in other places, such as just the Lambert, Blinn, Phong "material types/shaded surfaces", or as Metal, Plastic, Wood, etc. In game dev forums, people often talk about implementing a "material/effect system". Is the material not an instance of an effect? Ergo, if I had effect objects, stored in a collection, & each effect instance object with there own parameter setting, then there is no need for the concept of a material... Or am I interpreting it wrong? Please help by contributing your interpretations as I want to be clear on a distinction (if any), & don't want to miss out on the concept of a material if it should be implemented to follow the abstraction of the DirectX FX framework & COLLADA definitions closely.

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• Threads slowing down application and not working properly

  - by Belgin

  I'm making a software renderer which does per-polygon rasterization using a floating point digital differential analyzer algorithm. My idea was to create two threads for rasterization and have them work like so: one thread draws each even scanline in a polygon and the other thread draws each odd scanline, and they both start working at the same time, but the main application waits for both of them to finish and then pauses them before continuing with other computations. As this is the first time I'm making a threaded application, I'm not sure if the following method for thread synchronization is correct: First of all, I use two global variables to control the two threads, if a global variable is set to 1, that means the thread can start working, otherwise it must not work. This is checked by the thread running an infinite loop and if it detects that the global variable has changed its value, it does its job and then sets the variable back to 0 again. The main program also uses an empty while to check when both variables become 0 after setting them to 1. Second, each thread is assigned a global structure which contains information about the triangle that is about to be rasterized. The structures are filled in by the main program before setting the global variables to 1. My dilemma is that, while this process works under some conditions, it slows down the program considerably, and also it fails to run properly when compiled for Release in Visual Studio, or when compiled with any sort of -O optimization with gcc (i.e. nothing on screen, even SEGFAULTs). The program isn't much faster by default without threads, which you can see for yourself by commenting out the #define THREADS directive, but if I apply optimizations, it becomes much faster (especially with gcc -Ofast -march=native). N.B. It might not compile with gcc because of fscanf_s calls, but you can replace those with the usual fscanf, if you wish to use gcc. Because there is a lot of code, too much for here or pastebin, I created a git repository where you can view it. My questions are: Why does adding these two threads slow down my application? Why doesn't it work when compiling for Release or with optimizations? Can I speed up the application with threads? If so, how? Thanks in advance.

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• SAN performance issues storing SQL Server tempdb on a SAN that's being backed up

  - by user42724

  I'm afraid I don't know much about SAN's so please forgive my lack of detail or technical terms. As a developer I've just completed and put on an existing production system a new application but it would appear to have tipped the scales regarding the performance of the backups being taken from the SAN. As I understand it there's a mirror of the SAN being taken usually constantly at the block-level. However, there seem to be so many new writes to the disk that the SAN mirroring/backup process can no longer keep up. I believe I've narrowed this down to SQL Servers tempdb which exists on a drive that contributes the largest portion of the problem! In fact I think tempdb has be contributing the largest portion of the issues all along regardless of my application! My question therefore is whether the tempdb should ever be mirrored or backed on the SAN and whether anyone else has gone through this sort of pain already? I'm wondering whether it's a best practise to make sure that tempdb is never mirrored on a SAN simply because any writes to it don't need to be saved. This also raises a slightly connected question - is it better to rely on SQL Servers built-in database backups tools (DB in full-recovery mode with full/differential and transaction log backups) or, as is the case with our application, SQL server is in simple recovery mode and never backed up since the SAN is mirrored and backed up? Many thanks

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