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  • Static Typing and Writing a Simple Matrix Library

    - by duckworthd
    Aye it's been done a million times before, but damnit I want to do it again. I'm writing a simple Matrix Library for C++ with the intention of doing it right. I've come across something that's fairly obvious in mathematics, but not so obvious to a strongly typed system -- the fact that a 1x1 matrix is just a number. To avoid this, I started walking down the hairy path of matrices as a composition of vectors, but also stumbled upon the fact that two vectors multiplied together could either be a number or a dyad, depending on the orientation of the two. My question is, what is the right way to deal with this situation in a strongly typed language like C++ or Java?

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  • How do you calculate the reflex angle given to vectors in 3D space?

    - by Reimund
    I want to calculate the angle between two vectors a and b. Lets assume these are at the origin. This can be done with theta = arccos(a . b / |a| * |b|) However arccos gives you the angle in [0, pi], i.e. it will never give you an angle greater than 180 degrees, which is what I want. So how do you find out when the vectors have gone past the 180 degree mark? In 2D I would simply let the sign of the y-component on one of the vectors determine what quadrant the vector is in. But what is the easiest way to do it in 3D?

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  • SQL Server view: how to add missing rows using interpolation

    - by Christopher Klein
    Running into a problem. I have a table defined to hold the values of the daily treasury yield curve. It's a pretty simple table used for historical lookup of values. There are notibly some gaps in the table on year 4, 6, 8, 9, 11-19 and 21-29. The formula is pretty simple in that to calculate year 4 it's 0.5*Year3Value + 0.5*Year5Value. The problem is how can I write a VIEW that can return the missing years? I could probably do it in a stored procedure but the end result needs to be a view.

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  • NSPredicate as a constraint solver?

    - by Felixyz
    I'm working on a project which includes some slightly more complex dynamic layout of interface elements than what I'm used to. I always feel stupid writing complex code that checks if so-and-so is close to such-and-such and in that case move it x% in some direction, etc. That's just not how programming should be done. Programming should be as declarative as possible! Precisely because what I'm going to do is fairly simple, I thought it would be a good opportunity to try something new, and I thought of using NSPredicate as a simple constraints solver. I've only used NSPredicate for very simple tasks so far, but I know that it capable of much more. Are there any ideas, experiences, examples, warnings, insights that could be useful here? I'll give a very simple example so there will be something concrete to answer. How could I use NSPredicate to solve the following constraints: viewB.xmid = (viewB.leftEdge + viewB.width) / 2 viewB.xmid = max(300, viewA.rightEdge + 20 + viewB.width/2) ("viewB should be horizontally centered on coordinate 300, unless its left edge gets within 20 pixels of viewB's right edge, in which case viewA's left edge should stay fixed at 20 pixels to the right of viewB's right edge and viewA's horizontal center get pushed to the right.") viewA.rightEdge and viewB.width can vary, and those are the 'input variables'. EDIT: Any solution would probably have to use the NSExpression method -(id)expressionValueWithObject:(id)object context:(NSMutableDictionary *)context. This answer is relevant.

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  • Finding coordinates of a point between two points?

    - by Nicros
    Doing some 3D stuff in wpf- want to use a simpler test to see if everything is working (before moving to curves). The basic question is given two points x1,y1,z1 and x2,y2,z2 I have calculated the distance between the points. But how to find the coordinates of another point (x3,y3,z3) that lies on that line at some distance? I.e. if my line is 100 long between -50,0,0 and 50,0,0 what are the coordinates of the point at 100 * 0.1 along the line? I think this is a simple formula but I haven't found it yet....

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  • Alternative to as3isolib?

    - by tedw4rd
    Hi everyone, I've been working on a Flash game that involves an isometric space. I've been using as3isolib for a while now, and I'm less than impressed with how easy it is to use. Whether I'm approaching it the wrong way or it's just not that great to use is a question for another post. Anyways, I've been thinking of a different way to approach the problem of isometric positions, and I think I've got an idea that might work. Essentially, each object that is to be rendered to the iso-space maintains a 3-coordinate position. Those items are then registered with a camera that projects that 3-coordinate position to a 2-coordinate point on the screen according to the math on this Wikipedia article. Then, the MovieClip is added to the stage (or to the camera's MovieClip, perhaps) at that point, and at a child index of the point's y-value. That way, I figure objects that are closer to the camera will be "above" the objects further away, and will get rendered over them. So my question, then, is two-fold: Do you think this idea will work the way I think it will? Are there any existing 3D matrix/vector packages that I should look at? I know there's a Matrix3 class in Flex 3, but we're not using Flex for this game. Thanks!

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  • rotate a plane around a diagonal

    - by compie
    I would like to rotate a plane, not around a single (X or Y) axis, but around the diagonal (45 degrees between X and Y). How do I calculate the Rx and Ry given the Rdiagonal? (Rdiagonal is the amount of rotation I would like to achieve around the diagonal axis).

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  • implementation of interp1 function of MATLAB in J2ME

    - by Jeeka
    Hi, i am looking to implement the interp1, 1-D data interpolation (table lookup), function available in MATLAB in J2ME or JAVA. here is the link http://www.mathworks.com/access/helpdesk/help/techdoc/ref/interp1.html Is there any library available in J2ME or JAVA which has already implemented the same function ? If not can anybody help me in implementing interp1 function in J2ME or JAVA ?

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  • Solve equation from string to result in C

    - by Alexandre Cassagne
    Hi, I would like to know if anyone has info or experience on how to do something which sounds simple but doesn't look like it when trying to program it. The idea is : give a string containing an equation, such as : "2*x = 10" for example (this is simple, but it could get very complex, such as sqrt(54)*35=x^2; and so on....) and the program would return x = 5 and possibly give a log of how he got there. Is this doable ? If so, does anyone have a lead ? For info there is this site (http://www.numberempire.com/equationsolver.php) which does the same thing in PHP, but isn't open source. Thanks for any help !

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  • How to Create a Duotone Interpolation Color in GDI+ (.NET)?

    - by Otaku
    I have two colors that I need to linearly interpolate to create a duotone color based of another color's luminance value. Dim clr1 = Color.Black Dim clr2 = Color.FromArgb(224, 255, 165) Dim lum = Color.FromArgb(226, 189, 136).GetBrightness 'lum = 0.71 I know the result of this should be R=171, G=192, B=125, but I can't figure out how to do this. I've searched through SO quite a bit and all over Google, but have not discovered a way to produce this result. Can anyone help?

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  • Simple encryption - Sum of Hashes in C

    - by Dogbert
    I am attempting to demonstrate a simple proof of concept with respect to a vulnerability in a piece of code in a game written in C. Let's say that we want to validate a character login. The login is handled by the user choosing n items, (let's just assume n=5 for now) from a graphical menu. The items are all medieval themed: eg: _______________________________ | | | | | Bow | Sword | Staff | |-----------|-----------|-------| | Shield | Potion | Gold | |___________|___________|_______| The user must click on each item, then choose a number for each item. The validation algorithm then does the following: Determines which items were selected Drops each string to lowercase (ie: Bow becomes bow, etc) Calculates a simple string hash for each string (ie: `bow = b=2, o=15, w=23, sum = (2+15+23=40) Multiplies the hash by the value the user selected for the corresponding item; This new value is called the key Sums together the keys for each of the selected items; this is the final validation hash IMPORTANT: The validator will accept this hash, along with non-zero multiples of it (ie: if the final hash equals 1111, then 2222, 3333, 8888, etc are also valid). So, for example, let's say I select: Bow (1) Sword (2) Staff (10) Shield (1) Potion (6) The algorithm drops each of these strings to lowercase, calculates their string hashes, multiplies that hash by the number selected for each string, then sums these keys together. eg: Final_Validation_Hash = 1*HASH(Bow) + 2*HASH(Sword) + 10*HASH(Staff) + 1*HASH(Shield) + 6*HASH(Potion) By application of Euler's Method, I plan to demonstrate that these hashes are not unique, and want to devise a simple application to prove it. in my case, for 5 items, I would essentially be trying to calculate: (B)(y) = (A_1)(x_1) + (A_2)(x_2) + (A_3)(x_3) + (A_4)(x_4) + (A_5)(x_5) Where: B is arbitrary A_j are the selected coefficients/values for each string/category x_j are the hash values for each string/category y is the final validation hash (eg: 1111 above) B,y,A_j,x_j are all discrete-valued, positive, and non-zero (ie: natural numbers) Can someone either assist me in solving this problem or point me to a similar example (ie: code, worked out equations, etc)? I just need to solve the final step (ie: (B)(Y) = ...). Thank you all in advance.

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  • mystified by qr.Q(): what is an orthonormal matrix in "compact" form?

    - by gappy
    R has a qr() function, which performs QR decomposition using either LINPACK or LAPACK (in my experience, the latter is 5% faster). The main object returned is a matrix "qr" that contains in the upper triangular matrix R (i.e. R=qr[upper.tri(qr)]). So far so good. The lower triangular part of qr contains Q "in compact form". One can extract Q from the qr decomposition by using qr.Q(). I would like to find the inverse of qr.Q(). In other word, I do have Q and R, and would like to put them in a "qr" object. R is trivial but Q is not. The goal is to apply to it qr.solve(), which is much faster than solve() on large systems.

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  • Body CSS Gradient that Stops and Continues as Solid Color

    - by Alfo
    Something similar to this question has been asked here - HTML/CSS Gradient that stops at a perticular height and continues further with a solid color, but as far as I can see this doesn't work when using it on the body for a background color - which is what I want to achieve. Specifically, I would like it to be light blue at the top of the page, gradient into dark blue 200px further down, and then continue in dark blue for ever. Thanks to anybody who can help, Alfo.

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  • Rejigging a floating point equation ...

    - by Jamie
    I'd like to know if there is a way to improve the accuracy of calculating a slope. (This came up a few months back here). It seems by changing: float get_slope(float dXa, float dXb, float dYa, float dYb) { return (dXa - dXb)/(dYa - dYb); } to float get_slope(float dXa, float dXb, float dYa, float dYb) { return dXa/(dYa - dYb) - dXb/(dYa - dYb); } might be an improvement. Suggestions? Edit: It's precision I'm after, not efficiency.

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  • Where can I find BLAS example code (in Fortran)?

    - by Feynman
    I have been searching for decent documentation on blas, and I have found some 315 pages of dense material that ctrl-f does not work on. It provides all the information regarding what input arguments the routines take, but there are a LOT of input arguments and I could really use some example code. I am unable to locate any. I know there has to be some or no one would be able to use these libraries! Specifically, I use ATLAS installed via macports on a mac osx 10.5.8 and I use gfortran from gcc 4.4 (also installed via macports). I am coding in Fortran 90. I am still quite new to Fortran, but I have a fair amount of experience with mathematica, matlab, perl, and shell scripting. I would like to be able to initialize and multiply a dense complex vector by a dense symmetric (but not hermitian) complex matrix. The elements of the matrix are defined through a mathematical function of the indices--call it f(i,j). Could anyone provide some code or a link to some code?

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  • How to solve generic algebra using solver/library programmatically? Matlab, Mathematica, Wolfram etc?

    - by DevDevDev
    I'm trying to build an algebra trainer for students. I want to construct a representative problem, define constraints and relationships on the parameters, and then generate a bunch of Latex formatted problems from the representation. As an example: A specific question might be: If y < 0 and (x+3)(y-5) = 0, what is x? Answer (x = -3) I would like to encode this as a Latex formatted problem like. If $y<0$ and $(x+constant_1)(y+constant_2)=0$ what is the value of x? Answer = -constant_1 And plug into my problem solver constant_1 > 0, constant_1 < 60, constant_1 = INTEGER constant_2 < 0, constant_2 > -60, constant_2 = INTEGER Then it will randomly construct me pairs of (constant_1, constant_2) that I can feed into my Latex generator. Obviously this is an extremely simple example with no real "solving" but hopefully it gets the point across. Things I'm looking for ideally in priority order * Solve algebra problems * Definition of relationships relatively straight forward * Rich support for latex formatting (not just writing encoded strings) Thanks!

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  • Why is glpk-java.jar not the same across all platforms?

    - by pruefsumme
    I'm using glpk-java in one of my projects. It provides a JNI to GLPK, a free LP/MIP solver. To use it under different platforms, you need different shared libraries (libglpk.so under Linux, libglpk.dylib under Mac OS X, glpk.dll under Windows) which is fully understandable. In addition, a java library is needed: glpk-java.jar. It's created as part of the build process. I was wondering why this JAR file (which only contains .class files) is different under different platforms? I.e., I cannot use the same glpk-java.jar under Linux and Mac OS X which means that I cannot put this file under revision control.

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  • Converting Numpy Lstsq residual value to R^2

    - by whatnick
    I am performing a least squares regression as below (univariate). I would like to express the significance of the result in terms of R^2. Numpy returns a value of unscaled residual, what would be a sensible way of normalizing this. field_clean,back_clean = rid_zeros(backscatter,field_data) num_vals = len(field_clean) x = field_clean[:,row:row+1] y = 10*log10(back_clean) A = hstack([x, ones((num_vals,1))]) soln = lstsq(A, y ) m, c = soln [0] residues = soln [1] print residues

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  • Outer product using CBLAS

    - by The Dude
    I am having trouble utilizing CBLAS to perform an Outer Product. My code is as follows: //===SET UP===// double x1[] = {1,2,3,4}; double x2[] = {1,2,3}; int dx1 = 4; int dx2 = 3; double X[dx1 * dx2]; for (int i = 0; i < (dx1*dx2); i++) {X[i] = 0.0;} //===DO THE OUTER PRODUCT===// cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasTrans, dx1, dx2, 1, 1.0, x1, dx1, x2, 1, 0.0, X, dx1); //===PRINT THE RESULTS===// printf("\nMatrix X (%d x %d) = x1 (*) x2 is:\n", dx1, dx2); for (i=0; i<4; i++) { for (j=0; j<3; j++) { printf ("%lf ", X[j+i*3]); } printf ("\n"); } I get: Matrix X (4 x 3) = x1 (*) x2 is: 1.000000 2.000000 3.000000 0.000000 -1.000000 -2.000000 -3.000000 0.000000 7.000000 14.000000 21.000000 0.000000 But the correct answer is found here: https://www.sharcnet.ca/help/index.php/BLAS_and_CBLAS_Usage_and_Examples I have seen: Efficient computation of kronecker products in C But, it doesn't help me because they don't actually say how to utilize dgemm to actually do this... Any help? What am I doing wrong here?

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  • which default.list should i modify for default applications and what are the differences between the 2

    - by damien
    I would like to add miro to the default application GUI in system settings/default applications.I added ;miro.desktopnext to all rhythmbox.desktop entries eventually discovering if it was not added to audio/x-vorbis+ogg=rhythmbox.desktop as audio/x-vorbis+ogg=rhythmbox.desktop;miro.desktop it would not appear in the system settings/default applications drop down list for audio. I can find default.list in either /etc/gnome/defaults.list or /usr/share/applications/defaults.list modifying either gives me the same results.What is the difference and which is the correct list to modify?

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  • Remove hardware from "safely remove hardware" list on Windows 7

    - by ricsmania
    Hi, I have a USB wifi card (D-Link DWA-125) on a Windows 7 x64 computer. The problem is that the card appears on the "safely remove hardware" list, but I don't ever want to unplug it, so I would like to remove it from the list. So far I have only found solutions that mess with the registry (and don't really work properly) or that substitute the safely remove hardware with a third-party software. Or worse, hide the icon altogether. Yes, I do need the icon from USB drives and phones. So, is there a "clean" way to remove it from the list? Thanks.

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  • List files with last access date in linux

    - by kayaker243
    I'd like to clean up a server that my webmaster let turn into a mess. I know how to list all files not accessed within the last x days using find and -atime, but what I'm looking for is to come up with a listing of the last access date for files one level down in directory /foo: /foo/bar1.txt Dec 11, 2001 /foo/bar2.txt Nov 12, 2008 /foo/bar3.txt Jan 12, 2004 For folders one level down in directory /foo, list the date of the most recently accessed file within the directory (no limit on depth for identifying last access date) /foo/bar1/ Feb 13, 2012 /foo/bar2/ Oct 11, 2008 Where /foo/bar1/ has a file modified Jan 1, 1998 and Feb 13, 2012 and /foo/bar2/ has 30 files, most recent of which was accessed Oct 11, 2008. This question is similar to: http://stackoverflow.com/questions/5566310/how-to-recursively-find-and-list-the-latest-modified-files-in-a-directory-with-s but rather than the modification date, the date of interest is the last accessed date.

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  • (Apache) RedirectMatch regex to match all directories except those in my list

    - by dotben
    I need to 301 redirect all requests coming in for requests to http//server.com to be redirected to http//newserver.com unless the request is for an arbitary list of directories we are maintaining on the legacy server (eg server.com/foo or server.com/bar) I'm having a hard time working out how best to set this up and the regexs. EG, I need: http//server.com/page1 redirect to http//newserver.com/page1 http//server.com/dir1/page2 redirect to http//newserver.com/dir1/page2 http//server.com/foo to load as normal http//server.com/bar/baz.html to load as normal ... because 'foo' and 'bar' are in my list of legacy dirs. I'm wondering if the way to do this is to some how catch the matches in my list and then redirect anything else as a wildcard over to the new server -- but I can't make it work. Can anyone help me with some regex and rewrites for those please? Thanks (apologies for fudging the http:// in the urls, ServerFault thinks I'm posting hyperlinks and won't otherwise let me post this)

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