Algorithms

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Re: Interesting math magic? PIEBALDconsult17-Jul-07 7:37 PIEBALDconsult 17-Jul-07 7:37  Nah, Polish. Re: Interesting math magic? stevepqr7-Aug-07 6:07 stevepqr 7-Aug-07 6:07  is that a regular Polish guy or a reverse Polish? Apathy Rules - I suppose... Re: Interesting math magic? PIEBALDconsult17-Jul-07 7:36 PIEBALDconsult 17-Jul-07 7:36  Trick? What trick? It's the same as usual, but maybe helps some people keep the columns aligned properly. Re: Interesting math magic? Paul Conrad17-Jul-07 7:42 Paul Conrad 17-Jul-07 7:42  PIEBALDconsult wrote: It's the same as usual Yes it is. Just a different twist to it. "The clue train passed his station without stopping." - John Simmons / outlaw programmer Re: Interesting math magic? Bassam Abdul-Baki19-Jul-07 5:10 Bassam Abdul-Baki 19-Jul-07 5:10  The previous one was done with sticks, this one just makes it easier for the layman to understand. "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: Interesting math magic? _Damian S_17-Jul-07 16:56 _Damian S_ 17-Jul-07 16:56  That looked like a whole lot of hard work to me... just do it the normal way and be done with it!! ------------------------------------------- Don't walk in front of me, I may not follow; Don't walk behind me, I may not lead; Just bugger off and leave me alone!! Encoding vs Encrypting HakunaMatada13-Jul-07 0:22 HakunaMatada 13-Jul-07 0:22  Can someone tell me the difference between Encoding and Encryption? I tried searching high and low but couldn't get any answer. Thanks for your time. --- Hakuna-Matata It means no worries for the rest of your days... It's our problem free, Philosophy "I think my response was 'What idiot dreamed this up?'" -- Mary Ann Davidson, Oracle's chief security officer, in typical blunt manner, remembering her reaction to the company's scheme to brand its databases as "unbreakable." Re: Encoding vs Encrypting SHatchard13-Jul-07 0:59 SHatchard 13-Jul-07 0:59  I am not sure of an exact definition but as far as I am aware encoding is changing the way that the string is displayed, to mask it or change its format but is essentially in a fixed format and easily reversable. Encrypting masks the string with a key of some type (dependent on encryption type) and can usually be decrypted with the provided key. Some encryption cannot be unencrypted, such as MD5, but the same encrypted string can be compared for validation - useful for passwords. Not exactly a dictionary definition i know! Re: Encoding vs Encrypting Paul Conrad13-Jul-07 10:32 Paul Conrad 13-Jul-07 10:32  I'll add that MD5 isn't considered a strong encryption algorithm these days. "Any sort of work in VB6 is bound to provide several WTF moments." - Christian Graus Re: Encoding vs Encrypting CPallini13-Jul-07 2:57 CPallini 13-Jul-07 2:57  Encoding a string has to do with its internal representation. For instance, UTF8 or UNICODE maybe different internal representations of the same string. On the other hand, encryption aims to alter the string in such way that its original content is not recognizable by unauthorized people. Usually encryption imply encoding, usually encoding doens't imply encryption. 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: Encoding vs Encrypting Luc Pattyn13-Jul-07 10:25 Luc Pattyn 13-Jul-07 10:25  Hi, encoding is the process of mapping a collection of some type1 onto a collection of some type2, for instance you can encode the days of the week into the numbers 1 to 7; and the ASCII character encoding maps the character set we all know to a subset of 8-bit numbers. So it is a representation thing (a one-to-one mapping), often aiming at increasing readability or efficiency. encryption is the process of changing the representation in order to hide the content. the goal is not to make things easier, smaller, more economical; it is to hide the true meaning of things. Luc Pattyn try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] } catch { [Google] } Re: Encoding vs Encrypting MarkB77716-Jul-07 23:16 MarkB777 16-Jul-07 23:16  Wikipedia man!!! Mark Re: Encoding vs Encrypting Sathesh Sakthivel18-Jul-07 0:14 Sathesh Sakthivel 18-Jul-07 0:14  Encrypting a file means that one is altering it in order to conceal its contents. Encoding it means one is altering it because of technical reasons related to transmitting it (e.g., the Morse code). 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 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

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