Algorithms

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Newton Rapheson [modified] devvvy12-Jul-07 15:15 devvvy 12-Jul-07 15:15  Newton Rapheson ring a bell (Goal Seek function from Excel, that's the Algo they used)? Packaged bug free code anyone? Thanks a bunch. Re: Newton Rapheson cp987612-Jul-07 20:37 cp9876 12-Jul-07 20:37  You give no hint of what language you want, maybe Numerical Recipes is a good place to start - here is the 'c' version: Newton-Raphson Method[^] Peter "Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time." Re: Newton Rapheson devvvy13-Jul-07 1:27 devvvy 13-Jul-07 1:27  right! Numerical Recipes! Left school for sometime totally forget about it! Minimal Primes Bassam Abdul-Baki11-Jul-07 2:59 Bassam Abdul-Baki 11-Jul-07 2:59  Excellent read.[^] The PostScript file (year 2000) is more informative. "This perpetual motion machine she made is a joke. It just keeps going faster and faster. Lisa, get in here! In this house, we obey the laws of thermodynamics!" - Homer Simpson Web - Blog - RSS - Math - LinkedIn - BM Re: Minimal Primes Paul Conrad12-Jul-07 7:43 Paul Conrad 12-Jul-07 7:43  "Real programmers just throw a bunch of 1s and 0s at the computer to see what sticks" - Pete O'Hanlon Re: Minimal Primes Sathesh Sakthivel18-Jul-07 0:15 Sathesh Sakthivel 18-Jul-07 0:15  Regards, Satips. Don't walk in front of me, I may not follow; Don't walk behind me, I may not lead; Walk beside me, and just be my friend. - Albert Camus Re: Minimal Primes Russell'3-Aug-07 4:29 Russell' 3-Aug-07 4:29  Great Russell Interpolating Elevations Kyudos10-Jul-07 15:48 Kyudos 10-Jul-07 15:48  I have a set of X-Y-Z coordinate points defining a 3D space (actually contour data). Then supposing I want to find the elevation at point X-Y, would the following method work (or does anyone have any other, better, suggestions): 1) Flatten the XYZ data (i.e., take the X and Y coords) 2) Construct the 2D Delauney triangulation for the data set. 3) Find the triangle in which the point X-Y lies. 4) Use the XYZ coords of the vertices of the triangle to interpolate the elevation at XY. Of course the hard part is 3, but is the principle sound? Anyone know of any sample code I can refer to? (bearing in mind I'm not a mathematician or geometrician!) Cheers Re: Interpolating Elevations cp987611-Jul-07 20:43 cp9876 11-Jul-07 20:43  Years ago when I did some work in this area we had data on a rectangular grid - made things easy If you google on "gis interpolation" there are a lot of interesting hits, Peter "Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time." String - retrieving the first four jon-809-Jul-07 23:46 jon-80 9-Jul-07 23:46  I need to retrieve the first four alphanumeric characters from a string, basically, if I have "DE WINTER", I need to skip the third character and write "DEWI". Other than going through each substring is there some algorithm for this pattern? Jon Re: String - retrieving the first four CPallini10-Jul-07 0:26 CPallini 10-Jul-07 0:26  It actually depends on the language you're using: string objects usually offer a suitable Replace method. If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile. Re: String - retrieving the first four jon-8010-Jul-07 3:28 jon-80 10-Jul-07 3:28  I'm using JavaScript. Taking this point of view, the problem is that I need to iterate through each character in the source string and replace non-alphanumeric characters with a blank string (''). Jon Re: String - retrieving the first four CPallini10-Jul-07 3:58 CPallini 10-Jul-07 3:58  This http://www.w3schools.com/jsref/jsref_replace.asp[^]] doesn't help you, does it? If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile. Steganography algorithms?? Software_Specialist9-Jul-07 1:56 Software_Specialist 9-Jul-07 1:56  Hiya i am looking for algorithm for Steganography in .mp3 and .jpg.... I found few links while searching in google but all say something different...So any one here with a good algorithm for this task... And yeh i want to implement it in C#.Net..Yeh i know there are many articles for stego in this site but they are not for .jpg or .mp3.. thanks Re: Steganography algorithms?? Luc Pattyn9-Jul-07 2:30 Luc Pattyn 9-Jul-07 2:30  Search CodeProject for it, you will find several articles. And yes there are many ways to do it. Luc Pattyn try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] } catch { [Google] } Re: Steganography algorithms?? Software_Specialist9-Jul-07 2:42 Software_Specialist 9-Jul-07 2:42  I dont think there is any article for .mp3 and .jpg in code project...Thats what i mentioned in my post... Yeah there could be many ways, just trying to know which algo is the best way if somebody has already achieved that... anywayz... Thanks Re: Steganography algorithms?? Luc Pattyn9-Jul-07 3:01 Luc Pattyn 9-Jul-07 3:01  I dont know for mp3, I have seen several for JPEG. Luc Pattyn try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] } catch { [Google] } Re: Steganography algorithms?? Vasudevan Deepak Kumar17-Jul-07 6:45 Vasudevan Deepak Kumar 17-Jul-07 6:45  http://en.wikipedia.org/wiki/Steganography[^] Vasudevan Deepak Kumar Personal Homepage Tech Gossips linear algebra library ovoundaga8-Jul-07 2:03 ovoundaga 8-Jul-07 2:03  hi !i am writting a project where i have to deal with a lot of matrices and still a biginner in programming.i want to know if there is a library for linear algebra in c and where to get it.thanks!! Re: linear algebra library Stephen Hewitt8-Jul-07 15:03 Stephen Hewitt 8-Jul-07 15:03  If you're using C++ I'd go for Boost's uBLAS[^] library. If you are going to use C try the BLAS[^] library. Steve Re: I think this shouldn't be here... p_v_chaitanya2-Jul-07 1:51 p_v_chaitanya 2-Jul-07 1:51  Sure Sir, gonna delete this right away..... Am a newbie here and wanted to know more on Software Architecture with feedbacks and comments on topic I have raised at my blog pchaitanya.wordpress.com..... Any feedback would be highly appreciated.... Thanks, Chaitanya Chaitanya I think this shouldn't be here... CPallini2-Jul-07 1:47 CPallini 2-Jul-07 1:47  If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile. Quick Hit-Testing Ri Qen-Sin19-Jun-07 3:43 Ri Qen-Sin 19-Jun-07 3:43  For a 2-dimensional plane, I've implemented a function for determining whether a circle intersects a ray. Suppose there is one ray and many, many circles. How would I reduce the number of tests by selecting the circles that are certain or likely to be hit? ROFLOLMFAO Re: Quick Hit-Testing Luc Pattyn19-Jun-07 4:30 Luc Pattyn 19-Jun-07 4:30  Hi, lots can be done depending on circumstances. SCHEME 1 Assuming you are only interested in a finite and rectangular part of the 2D plane, you could divide the area in a number of smaller rectangles. Say 16*16 rectangles. Now a ray would intersect only some of these rectangles, so we are only interested in those circles that partially cover those rectangles. Assuming your circles are static, that can be precalculated and stored: for each record, you can hold a list of crossing circles. So now it is a matter of finding the rectangles crossed, then scanning the circles listed for these rectangles. WARNING: things must be organized in such a way that the same circle is not tested again for different rectangles; a boolean flag might help. SCHEME 2 Assuming (most of) the circles are fairly small with respect to the entire area, if the ray does not cross the entire area, but is restricted to some X-range (for a steep ray) or some Y-range, one could easily eliminate all circles that lie fully outside said X or Y-range. Hope this helps. Luc Pattyn [My Articles] [Forum Guidelines] Re: Quick Hit-Testing Ri Qen-Sin19-Jun-07 6:09 Ri Qen-Sin 19-Jun-07 6:09  Thank you for your input. I have already thought about SCHEME 1. The problem is, the circles are not static. They move around. They represent players on a map, and the line represents the path that a bullet takes. After some more thought about the problem, I realized that while we can't elimenate unnecessary tests altogether, we can cut out a good portion of the tests in some circumstances. This might involve maintaining certain properties before the actual hit testing occurs (like how order is maintained for a balanced search tree before a search is performed). I will outline my approach below (and you can judge my methods): A rectangular plane (named: MAP) is created which everything else will be relative to. MAP is subdivided into regions. These regions are squares. They contain references to circles. The length and width of the region are set such that it is not smaller than the largest diameter of a circle. These regions are addressed by indices. The indices are directly related to the region's offset from the origin on MAP. A circle (named: CHAR1) is created on MAP with a radius no greater than half a region's length. (This is important later on when we try to determine what regions get tested.) CHAR1 is added to the region that it is in. (The circle's boundaries may cross into one or more other regions.) Its region will now have a reference to it. CHAR1 moves and it crosses its region's boundaries. It has crossed into another region, so the region's references to CHAR1 are deleted, and the current region CHAR1 resides in creates a reference to CHAR1. (Regions are synchronized with the circle's location.) Another circle (named: CHAR2) is created on MAP. It fires a projectile that follows a line (named: PATH). Now here is the tricky part (I don't even know if it works.): With PATH defined by y = mx + b, create 2 more lines that are parrallel to PATH and are separated by an a perpendicular distance that is equal to the greatest possible radius of a circle (a limit which is artificially imposed). The lines are created on with sides of PATH. The three lines intersect all the regions that should be tested. (Hit-testing with squares should be much more efficient than hit testing with circles.) So now that we have 3 lines, we just plugin values for X in increments of the width of the region starting from the position of CHAR2. We get coordinates that hit every region that needs to be tested. Suppose the indices of the regions use the format [x, y] in increments of 1, and region's corner defined by it's coordinates multiplied by the region length/width, then we could do an integer division on the coordinates given by plugging in X values into the line equations and get the regions that should be tested. ROFLOLMFAO

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