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  • Plotting an Arc in Discrete Steps

    - by phobos51594
    Good afternoon, Background My question relates to the plotting of an arbitrary arc in space using discrete steps. It is unique, however, in that I am not drawing to a canvas in the typical sense. The firmware I am designing is for a gcode interpreter for a CNC mill that will translate commands into stepper motor movements. Now, I have already found a similar question on this very site, but the methodology suggested (Bresenham's Algorithm) appears to be incompatable for moving an object in space, as it only relies on the calculation of one octant of a circle which is then mirrored about the remaining axes of symmetry. Furthermore, the prescribed method of calculation an arc between two arbitrary angles relies on trigonometry (I am implementing on a microcontroller and would like to avoid costly trig functions, if possible) and simply not taking the steps that are out of the range. Finally, the algorithm only is designed to work in one rotational direction (e.g. counterclockwise). Question So, on to the actual question: Does anyone know of a general-purpose algorithm that can be used to "draw" an arbitrary arc in discrete steps while still giving respect to angular direction (CW / CCW)? The final implementation will be done in C, but the language for the purpose of the question is irrelevant. Thank you in advance. References S.O post on drawing a simple circle using Bresenham's Algorithm: "Drawing" an arc in discrete x-y steps Wiki page describing Bresenham's Algorithm for a circle http://en.wikipedia.org/wiki/Midpoint_circle_algorithm Gcode instructions to be implemented (see. G2 and G3) http://linuxcnc.org/docs/html/gcode.html

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  • A good data model for finding a user's favorite stories

    - by wings
    Original Design Here's how I originally had my Models set up: class UserData(db.Model): user = db.UserProperty() favorites = db.ListProperty(db.Key) # list of story keys # ... class Story(db.Model): title = db.StringProperty() # ... On every page that displayed a story I would query UserData for the current user: user_data = UserData.all().filter('user =' users.get_current_user()).get() story_is_favorited = (story in user_data.favorites) New Design After watching this talk: Google I/O 2009 - Scalable, Complex Apps on App Engine, I wondered if I could set things up more efficiently. class FavoriteIndex(db.Model): favorited_by = db.StringListProperty() The Story Model is the same, but I got rid of the UserData Model. Each instance of the new FavoriteIndex Model has a Story instance as a parent. And each FavoriteIndex stores a list of user id's in it's favorited_by property. If I want to find all of the stories that have been favorited by a certain user: index_keys = FavoriteIndex.all(keys_only=True).filter('favorited_by =', users.get_current_user().user_id()) story_keys = [k.parent() for k in index_keys] stories = db.get(story_keys) This approach avoids the serialization/deserialization that's otherwise associated with the ListProperty. Efficiency vs Simplicity I'm not sure how efficient the new design is, especially after a user decides to favorite 300 stories, but here's why I like it: A favorited story is associated with a user, not with her user data On a page where I display a story, it's pretty easy to ask the story if it's been favorited (without calling up a separate entity filled with user data). fav_index = FavoriteIndex.all().ancestor(story).get() fav_of_current_user = users.get_current_user().user_id() in fav_index.favorited_by It's also easy to get a list of all the users who have favorited a story (using the method in #2) Is there an easier way? Please help. How is this kind of thing normally done?

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  • Identifying the GeoPoint that trigger an onTap call

    - by Akroy
    I'm developing a Google Maps app on Android. I have a number of GeoPoints that I'm displaying by adding them as OverlayItems to an ItemizedOverlay. This works well for displaying them and bringing up a nice box when I click them, however I'm trying to put info in the box it brings up. Thus, I've extended ItemizedOverlay with my own class, and I'm overriding onTap (final GeoPoint p, final MapView mapView). At first I thought that this would be very simple, as one of the parameters is the GeoPoint, so I would know exactly which GeoPoint was clicked. However, from what I can tell, the GeoPoint argument there is the GeoPoint for where the user actually touched. Given the range the user can touch and still trigger the onTap, that GeoPoint isn't very helpful for knowing precisely which GeoPoint was actually touched. I'm currently checking the parameter GeoPoint against all my existing GeoPoints and seeing which it's closest to. This seems like a super hacky abstraction inversion. Is there a better way to know what was actually tapped?

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  • How to check if new version of Chrome is available?

    - by serg
    I am trying to build an extension that would notify a user when new version of Chrome is available. I tried to inspect network traffic when Chrome is checking for an update and it is sending a request to http://74.125.95.113/service/update2?w=3:{long_encoded_string} page that returns XML with information I need: <?xml version="1.0" encoding="UTF-8"?> <gupdate xmlns="http://www.google.com/update2/response" protocol="2.0" server="prod"> <daystart elapsed_seconds="31272"/> <app appid="{8A69D345-D564-463C-AFF1-A69D9E530F96}" status="ok"> <updatecheck status="noupdate"/> <ping status="ok"/> </app> </gupdate> Besides sending {long_encoded_string} as URL parameter it is also sending some encoded cookie. Maybe someone familiar with Chrome build process can shed some light on those encoded strings and how to build them? Maybe there is another easier way (I have a feeling that string encoding is a dead end for me)?

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  • Chrome extension javascript array bug?

    - by Wayne Werner
    Hi, I'm working on a Google Chrome extension. In the popup I have the following code: var bookmarks = []; function appendBMTnode(node){ bookmarks.push([node[0].title, node[0].id]); } function addchildren(results){ for(x = 0; x < results.length; x++){ bookmarks.push([results[x].title, results[x].id]); chrome.bookmarks.getChildren(results[x].id, addchildren); } } function getallbookmarks(){ chrome.bookmarks.get('0', appendBMTnode); chrome.bookmarks.getChildren('0', addchildren); } console.debug(bookmarks.length); console.debug(bookmarks); Now, I would assume that the first command would issue the # of bookmarks I have. Indeed, when I use Chrome's debugger and add bookmarks.length to the watch list, 418 is the value. In the console of the debugger I can write bookmarks.length and it will give me the correct length. I can type for(x = 0; x < bookmarks.length; x++){ console.debug(bookmarks[x]); } and I get string representations of each inner array. However, that original console.debug(bookmarks.length) gives an output of zero. And if I add console.debug(bookmarks[0]); to the popup.html it tells me that the value is undefined. This seems like a bug to me, but my real question is how can I iterate over this list? Thanks

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  • Books on string algorithms

    - by Max
    There have been numerous posts on string algorithms: http://stackoverflow.com/questions/246961/algorithm-to-find-similar-text, http://stackoverflow.com/questions/451884/similar-string-algorithm, http://stackoverflow.com/questions/613133/efficient-string-matching-algorithm However, no general literature was mentioned. Could anyone recommend a book(s) that would thoroughly explore various string algorithms? The topic which is of special interest is approximate string matching [things like google-offered corrected search string variants :) ]. Thanks a lot for advice.

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  • List modification in Python

    - by user2945143
    We are given an algorithm to modify a list of numbers from 1 to 28. There are 5 steps in the algorithm. We have written functions for each step (all correct). We need to write a function that combines all 5 steps. The algorithm modifies the list to get a value. Each time you get a new value, you use the list created by the algorithm from the previous step. This is what we have gotten so far for the code: get_card_at_top_index(insert_top_to_bottom(triple_cut((move_joker_2( move_joker_1(deck)))))) When we run the code to generate the get_card_at_top_index, the first answer is correct. However, the rest are not. Instead of using from the new list, python uses the value that it generated from the last step. What did we do wrong? UPDATE: The other 5 codes passed the tests, they are correct. Code 1 (List) = list1 Code 2 (list1) = list2 Code 3 (list2) = list3 Code 4 (list3) = list4 Code 5 (list4) = list5 we generate a number from 5. We need to run the algorithm again to generate 25 more numbers. We will use list 5 start from step 1

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  • How to find pythagorean triplets in an array faster than O(N^2)?

    - by SS
    Can someone suggest an algorithm that finds all Pythagorean triplets among numbers in a given array? If it's possible, please, suggest an algorithm faster than O(n2). Pythagorean triplet is a set {a,b,c} such that a2 = b2 + c2. Example: for array [9, 2, 3, 4, 8, 5, 6, 10] the output of the algorithm should be {3, 4, 5} and {6, 8, 10}.

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  • question on find value in array

    - by davit-datuashvili
    i have seen a few days ago such problem there is given two array find elements which are common of these array one of the solution was sort big array and then use binary search algorithm and also there is another algorithm- brute-force algorithm for (int i=0;i<array1.length;i++){ for (int j=0;j<array2.length;j++){ if (array1[i]==array2[j]){ //code here } } it's complexity is O(array1.length*array2.length); and i am interested the first method's complexity is also same yes? because we should sort array first and then use search method binary search algorithm's complexity is log_2(n) so it means that total time will be array.length*log_2(n) and about sort? please explain me which is better

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  • How Google does disaster recovery

    Will you be ready when disaster strikes? It's an uncomfortable question for many IT administrators, because answering it with confidence usually requires boatloads of money, immense complexity, and...

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  • Splitting values into groups evenly

    - by Paul Knopf
    Let me try to explain the situation the best I can. Lets say I have 3 values 1, 2, 3 I tell an algorithm to split this values into x columns. Lets say x = 2 for clarification. The algorithm determines that the group of values is best put into two columns the following way. 1st column 2nd column --------------------------- 1 3 2 Each column has an even number (totals, not literals) value. Now lets say I have the following values 7, 8, 3, 1, 4 I tell the algorithm that I want the values split into 3 columns. The algorithm now tells me that the following is the best fit. 1st column 2nd column 3rd column 8 7 3 1 4 Notice how the columns arent quiet even, but it is as close as it can get. A little over and a little under is considered ok, as long as the list is AS CLOSE TO EVEN AS IT CAN BE. Anybody got any suggestions? Know any good methods of doing this?

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  • bulls and cows game -- programming algorithm(python)

    - by IcyFlame
    This is a simulation of the game Cows and Bulls with three digit numbers I am trying to get the number of cows and bulls between two numbers. One of which is generated by the computer and the other is guessed by the user. I have parsed the two numbers I have so that now I have two lists with three elements each and each element is one of the digits in the number. So: 237 will give the list [2,3,7]. And I make sure that the relative indices are maintained.the general pattern is:(hundreds, tens, units). And these two lists are stored in the two lists: machine and person. ALGORITHM 1 So, I wrote the following code, The most intuitive algorithm: cows and bulls are initialized to 0 before the start of this loop. for x in person: if x in machine: if machine.index(x) == person.index(x): bulls += 1 print x,' in correct place' else: print x,' in wrong place' cows += 1 And I started testing this with different type of numbers guessed by the computer. Quite randomly, I decided on 277. And I guessed 447. Here, I got the first clue that this algorithm may not work. I got 1 cow and 0 bulls. Whereas I should have got 1 bull and 1 cow. This is a table of outputs with the first algorithm: Guess Output Expected Output 447 0 bull, 1 cow 1 bull, 1 cow 477 2 bulls, 0 cows 2 bulls, 0 cows 777 0 bulls, 3 cows 2 bulls, 0 cows So obviously this algorithm was not working when there are repeated digits in the number randomly selected by the computer. I tried to understand why these errors are taking place, But I could not. I have tried a lot but I just could not see any mistake in the algorithm(probably because I wrote it!) ALGORITHM 2 On thinking about this for a few days I tried this: cows and bulls are initialized to 0 before the start of this loop. for x in range(3): for y in range(3): if x == y and machine[x] == person[y]: bulls += 1 if not (x == y) and machine[x] == person[y]: cows += 1 I was more hopeful about this one. But when I tested this, this is what I got: Guess Output Expected Output 447 1 bull, 1 cow 1 bull, 1 cow 477 2 bulls, 2 cows 2 bulls, 0 cows 777 2 bulls, 4 cows 2 bulls, 0 cows The mistake I am making is quite clear here, I understood that the numbers were being counted again and again. i.e.: 277 versus 477 When you count for bulls then the 2 bulls come up and thats alright. But when you count for cows: the 7 in 277 at units place is matched with the 7 in 477 in tens place and thus a cow is generated. the 7 in 277 at tens place is matched with the 7 in 477 in units place and thus a cow is generated.' Here the matching is exactly right as I have written the code as per that. But this is not what I want. And I have no idea whatsoever on what to do after this. Furthermore... I would like to stress that both the algorithms work perfectly, if there are no repeated digits in the number selected by the computer. Please help me with this issue. P.S.: I have been thinking about this for over a week, But I could not post a question earlier as my account was blocked(from asking questions) because I asked a foolish question. And did not delete it even though I got 2 downvotes immediately after posting the question.

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  • How can I read/write data from a file?

    - by samy
    I'm writing a simple chrome extension. I need to create the ability to add sites URLs to a list, or read from the list. I use the list to open the sites in the new tabs. I'm looking for a way to have a data file I can write to, and read from. I was thinking on XML. I read there is a problem changing the content of files with Javascript. Is XML the right choice for this kinda thing? I should add that there is no web server, and the app will run locally, so maybe the problem websites are having are not same as this. Before I wrote this question, I tried one thing, and started to feel insecure because it didn't work. I made a XML file called Site.xml: <?xml version="1.0" encoding="utf-8" ?> <Sites> <site> <url> http://www.sulamacademy.com/AddMsgForum.asp?FType=273171&SBLang=0&WSUAccess=0&LocSBID=20375 </url> </site> <site> <url> http://www.wow.co.il </url> </site> <site> <url> http://www.Google.co.il </url> </site> I made this script to read the data from him, and put in on the html file. function LoadXML() { var ajaxObj = new XMLHttpRequest(); ajaxObj.open('GET', 'Sites.xml', false); ajaxObj.send(); var myXML = ajaxObj.responseXML; document.write('<table border="2">'); var prs = myXML.getElementsByTagName("site"); for (i = 0; i < prs.length; i++) { document.write("<tr><td>"); document.write(prs[i].getElementsByName("url")[0].childNode[0].nodeValue); document.write("</td></tr>"); } document.write("</table"); }

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  • Chrome extension: sendMessage doesn't work

    - by user3334776
    I've already read the documentation from Google on 'message passing' a few times and have probably looked at over 10 other questions with the same problem and already tried quiet a few variations of most of their "solutions" and of what I have below... This is black magic, right? Either way, here it goes. Manifest File: { "manifest_version" : 2, "name" : "Message Test", "version" : "1.0", "browser_action": { "default_popup": "popup.html" }, "background": { "scripts": ["background.js"] }, "content_scripts": [ { "matches" : ["<all_urls>"], "js": ["message-test.js"] } ] } I'm aware extensions aren't suppose to use inline JS, but I'm leaving this in so the original question can be left as it was since I still can't get the message to send from the background page, When I switch from the popup to the background, I removed the appropriate lines from the manifest.json popup.html file: <html> <head> <script> chrome.tabs.query({active: true, currentWindow: true}, function(tabs) { chrome.tabs.sendMessage(tabs[0].id, {greeting: "hello", theMessage: "Why isn\'t this working?"}, function(response) { console.log(response.farewell); }); }); </script> </head> <body> </body> </html> OR background.js file: chrome.tabs.query({active: true, currentWindow: true}, function(tabs) { chrome.tabs.sendMessage(tabs[0].id, {greeting: "hello", theMessage: "Why isn\'t this working?"}, function(response) { console.log(response.farewell); }); }); message-test.js file: var Mymessage; chrome.runtime.onMessage.addListener(function(message, sender, sendResponse) { if (message.greeting == "hello"){ Mymessage = message.theMessage; alert(Mymessage); } else{ sendResponse({}); } }); No alert(Mymessage) goes off. I'm also trying to execute this after pressing a button from a popup and having a window at a specified url, but that's a later issue. The other files can be found here except with the background.js content wrapped in an addEventListener("click"....: http://pastebin.com/KhqxLx5y AND http://pastebin.com/JaGcp6tj

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  • How can I remove rows with unique values? As in only keeping rows with duplicate values?

    - by user1456405
    Here's the conundrum, I'm a complete and utter noob when it comes to programming. I understand the basics, but am still learning javascript. I have a spreadsheet of surveys, in which I need to see how particular users have varied over time. As such, I need to disregard all rows with unique values in a particular column. The data looks like this: Response Date Response_ID Account_ID Q.1 10/20/2011 12:03:43 PM 23655956 1168161 8 10/20/2011 03:52:57 PM 23660161 1168152 0 10/21/2011 10:55:54 AM 23672903 1166121 7 10/23/2011 04:28:16 PM 23694471 1144756 9 10/25/2011 06:30:52 AM 23732674 1167449 7 10/25/2011 07:52:28 AM 23734597 1087618 5 I've found a way to do so in VBA, which sucks as I have to use excel, per below: Sub Del_Unique() Application.ScreenUpdating = False Columns("B:B").Insert Shift:=xlToRight Columns("A:A").Copy Destination:=Columns("B:B") i = Application.CountIf(Range("A:A"), "<>") + 50 If i > 65536 Then i = 65536 Do If Application.CountIf(Range("B:B"), Range("A" & i)) = 1 Then Rows(i).Delete End If i = i - 1 Loop Until i = 0 Columns("B:B").Delete Application.ScreenUpdating = True End Sub But that requires mucking about. I'd really like to do it in Google Spreadsheets with a script that won't have to be changed. Closest I can get is retrieving all duplicate user ids from the range, but can't associate that with the row. That code follows: function findDuplicatesInSelection() { var activeRange = SpreadsheetApp.getActiveRange(); var values = activeRange.getValues(); // values that appear at least once var once = {}; // values that appear at least twice var twice = {}; // values that appear at least twice, stored in a pretty fashion! var final = []; for (var i = 0; i < values.length; i++) { var inner = values[i]; for (var j = 0; j < inner.length; j++) { var cell = inner[j]; if (cell == "") continue; if (once.hasOwnProperty(cell)) { if (!twice.hasOwnProperty(cell)) { final.push(cell); } twice[cell] = 1; } else { once[cell] = 1; } } } if (final.length == 0) { Browser.msgBox("No duplicates found"); } else { Browser.msgBox("Duplicates are: " + final); } } Anyhow, sorry if this is the wrong place or format, but half of what I've found so far has been from stack, I thought it was a good place to start. Thanks!

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  • « Google Wave » devient « Apache Wave », la Apache Software Foundation accepte officiellement de reprendre le projet

    « Google Wave » devient « Apache Wave » La Apache Software Foundation accepte officiellement de reprendre le projet Mise à jour du 09/12/10 La fondation Apache et Google viennent de le confirmer, Wave intègre officiellement le programme d'incubation de la fondation après que celle-ci a finalement donné son feu vert pour la migration (lire ci-avant). Le comité de pilotage du projet est modifié en conséquence, avec notamment l'arrivée de deux membre de Novell (également très impliqué ...

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