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  • Orbital equations, and power required to run them

    - by Adam Davis
    Due to a discussion on the SO IRC today, I'm curious about orbital mechanics, and The equations needed to solve orbital problems The computing power required to solve complex problems The question in particular is calculating when the Earth will plow into the Sun (or vice versa, depending on the frame of reference). I suspect that all the gravitational pulls within our solar system may need to be calculated, which makes me wonder what type of computer cluster is required, or can this be done on a single box? I don't have the experience to do a back of the napkin test here, but perhaps you do? Also, much thx to Gortok for the original inspiration (see comments).

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  • flood fill algorithm

    - by user335593
    i want to implement the flood fill algorthm...so that when i get the x and y co-od of a point...it should start flooding from that point and fill till it finds a boundary but it is not filling the entire region...say a pentagon this is the code i am using void setpixel(struct fill fillcolor,int x,int y) { glColor3f(fillcolor.r,fillcolor.g,fillcolor.b); glBegin(GL_POINTS); glVertex2i(x,y); glEnd(); glFlush(); } struct fill getpixcol(int x,int y) { struct fill gotpixel; glReadPixels(x,y,1,1,GL_RGB,GL_UNSIGNED_BYTE,pick_col); gotpixel.r =(float) pick_col[0]/255.0; gotpixel.g =(float) pick_col[1]/255.0; gotpixel.b =(float) pick_col[2]/255.0; return(gotpixel); } void floodFill(int x, int y,struct fill fillcolor,struct fill boundarycolor) { struct fill tmp; // if ((x < 0) || (x >= 500)) return; // if ((y < 0) || (y >= 500)) return; tmp=getpixcol(x,y); while (tmp.r!=boundarycolor.r && tmp.g!=boundarycolor.g && tmp.b!=boundarycolor.b) { setpixel(fillcolor,x,y); setpixel(fillcolor,x+1,y); setpixel(fillcolor,x,y+1); setpixel(fillcolor,x,y-1); setpixel(fillcolor,x-1,y); floodFill(x-1,y+1,fillcolor,boundarycolor); floodFill(x-1,y,fillcolor,boundarycolor); floodFill(x-1,y-1,fillcolor,boundarycolor); floodFill(x,y+1,fillcolor,boundarycolor); floodFill(x,y-1,fillcolor,boundarycolor); floodFill(x+1,y+1,fillcolor,boundarycolor); floodFill(x+1,y,fillcolor,boundarycolor); floodFill(x+1,y-1,fillcolor,boundarycolor); } }

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  • Better way to summarize data about stop times?

    - by Vimvq1987
    This question is close to this: http://stackoverflow.com/questions/2947963/find-the-period-of-over-speed Here's my table: Longtitude Latitude Velocity Time 102 401 40 2010-06-01 10:22:34.000 103 403 50 2010-06-01 10:40:00.000 104 405 0 2010-06-01 11:00:03.000 104 405 0 2010-06-01 11:10:05.000 105 406 35 2010-06-01 11:15:30.000 106 403 60 2010-06-01 11:20:00.000 108 404 70 2010-06-01 11:30:05.000 109 405 0 2010-06-01 11:35:00.000 109 405 0 2010-06-01 11:40:00.000 105 407 40 2010-06-01 11:50:00.000 104 406 30 2010-06-01 12:00:00.000 101 409 50 2010-06-01 12:05:30.000 104 405 0 2010-06-01 11:05:30.000 I want to summarize times when vehicle had stopped (velocity = 0), include: it had stopped since "when" to "when" in how much minutes, how many times it stopped and how much time it stopped. I wrote this query to do it: select longtitude, latitude, MIN(time), MAX(time), DATEDIFF(minute, MIN(Time), MAX(time)) as Timespan from table_1 where velocity = 0 group by longtitude,latitude select DATEDIFF(minute, MIN(Time), MAX(time)) as minute into #temp3 from table_1 where velocity = 0 group by longtitude,latitude select COUNT(*) as [number]from #temp select SUM(minute) as [totaltime] from #temp3 drop table #temp This query return: longtitude latitude (No column name) (No column name) Timespan 104 405 2010-06-01 11:00:03.000 2010-06-01 11:10:05.000 10 109 405 2010-06-01 11:35:00.000 2010-06-01 11:40:00.000 5 number 2 totaltime 15 You can see, it works fine, but I really don't like the #temp table. Is there anyway to query this without use a temp table? Thank you.

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  • Trying to generate all sequences of specified numbers up to a max sum

    - by Stecy
    Hi, Given the following list of descending unique numbers (3,2,1) I wish to generate all the sequences consisting of those numbers up to a maximum sum. Let's say that the sum should be below 10. Then the sequences I'm after are: 3 3 3 3 3 2 1 3 3 2 3 3 1 1 1 3 3 1 1 3 3 1 3 3 3 2 2 2 3 2 2 1 1 3 2 2 1 3 2 2 3 2 1 1 1 1 3 2 1 1 1 3 2 1 1 3 2 1 3 2 3 1 1 1 1 1 1 3 1 1 1 1 1 3 1 1 1 1 3 1 1 1 3 1 1 3 1 3 2 2 2 2 1 2 2 2 2 2 2 2 1 1 1 2 2 2 1 1 2 2 2 1 2 2 2 2 2 1 1 1 1 1 2 2 1 1 1 1 2 2 1 1 1 2 2 1 1 2 2 1 2 2 2 1 1 1 1 1 1 1 2 1 1 1 1 1 1 2 1 1 1 1 1 2 1 1 1 1 2 1 1 1 2 1 1 2 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I'm sure that there's a "standard" way to generate this. I thought of using linq but can't figure it out. Also, I am trying a stack based approach but I am still not successful. Any idea?

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  • Point data structure for a sketching application

    - by bebraw
    I am currently developing a little sketching application based on HTML5 Canvas element. There is one particular problem I haven't yet managed to find a proper solution for. The idea is that the user will be able to manipulate existing stroke data (points) quite freely. This includes pushing point data around (ie. magnet tool) and manipulating it at whim otherwise (ie. altering color). Note that the current brush engine is able to shade by taking existing stroke data in count. It's a quick and dirty solution as it just iterates the points in the current stroke and checks them against a distance rule. Now the problem is how to do this in a nice manner. It is extremely important to be able to perform efficient queries that return all points within given canvas coordinate and radius. Other features, such as space usage, should be secondary to this. I don't mind doing some extra processing between strokes while the user is not painting. Any pointers are welcome. :)

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  • Single dimension peak fitting

    - by bufferz
    I have a single dimensional array of floating point values (c# doubles FYI) and I need to find the "peak" of the values ... as if graphed. I can't just take the highest value, as the peak is actually a plateau that has small fluctuations. This plateau is in the middle of a bunch of noise. I'm looking find a solution that would give me the center of this plateau. An example array might look like this: 1,2,1,1,2,1,3,2,4,4,4,5,6,8,8,8,8,7,8,7,9,7,5,4,4,3,3,2,2,1,1,1,1,1,2,1,1,1,1 where the peak is somewhere in the bolded section. Any ideas?

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  • How to scale rotated objects properly in Actionscript 3?

    - by Tom
    This is unfortunately a quite complex issue to explain, so please don't get discouraged by the wall of text - it's there for a reason. ;) I'm working on a transformation manager for flash, written with Actionscript 3. Users can place objects on the screen, for example a rectangle. This rectangle can then be selected and transformed: move, scale or rotate. Because flash by default rotates around the top left point of the object, and I want it to rotate around the center, I created a wrapper setup for each display object (eg. a rectangle). This is how the wrappers are setup: //the position wrapper makes sure that we do get the top left position when we access x and y var positionWrapper:Sprite = new Sprite(); positionWrapper.x = renderObject.x; positionWrapper.y = renderObject.y; //set the render objects location to center at the rotation wrappers top left renderObject.x = 0 - renderObject.width / 2; renderObject.y = 0 - renderObject.height / 2; //now create a rotation wrapper, at the center of the display object var rotationWrapper:Sprite = new Sprite(); rotationWrapper.x = renderObject.width / 2; rotationWrapper.y = renderObject.height / 2; //put the rotation wrapper inside the position wrapper and the render object inside the rotation wrapper positionWrapper.addChild(rotationWrapper); rotationWrapper.addChild(renderObject); Now, the x and y of the object can be accessed and set directly: mainWrapper.x or mainWrapper.y. The rotation can be set and accessed from the child of this main wrapper: mainWrapper.getChildAt(0).rotation. Finally, the width and height of the display object can be retreived and set by getting the child of the rotation wrapper and accessing the display object directly. An example on how I access them: //get wrappers and render object var positionWrapper:Sprite = currentSelection["render"]; var rotationWrapper:Sprite = positionWrapper.getChildAt(0) as Sprite; var renderObject:DisplayObject = rotationWrapper.getChildAt(0); This works perfectly for all initial transformations: moving, scaling and rotating. However, the problem arises when you first rotate an object (eg. 45 degrees) and then scale it. The scaled object is getting out of shape and doesn't scale as it should. This for example happens when you scale to the left. Scaling left is basically adding n width to the object and then reduce the x coord of the position wrapper by n too: renderObject.width -= diffX; positionWrapper.x += diffX; This works when the object is not rotated. However, when it is, the position wrapper won't be rotated as it is a parent of the rotation wrapper. This will make the position wrapper move left horizontally while the width of the object is increased diagonally. I hope this makes any sense, if not, please tell me and I'll try to elaborate more. Now, to the question: should I use a different kind of setup, system or structure? Should I maybe use matrixes, if so, how would you keep a static width/height after rotation? Or how do I fix my current wrapper system for scaling after rotation? Any help is appreciated.

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  • Graph diffing and versioning tool

    - by hashable
    I am working with a team that edits large DAGs represented as single files. Currently we are unable to work with multiple users concurrently modifying the DAG. Is there a tool (somewhat like the Eclipse SVN plugin) that can do do revision control on the file (manage timestamps/revision stamps) to identify incoming/outgoing/conflicting changes (Node/Link insertion/deletion/modification) and merge changes just like programmers do with source code files? The system should be able to do dependency management also. E.g. an incoming Link must not be accepted when one of the two Nodes is absent. That is, it should not "break" the existing DAG by allowing partial updates. If there is a framework to do this using generic "Node" and "Link" interfaces? Note: I am aware of Protege and its plugins. They currently do not satisfy my requirements.

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  • Generate 2D cross-section polygon from 3D mesh

    - by nornagon
    I'm writing a game which uses 3D models to draw a scene (top-down orthographic projection), but a 2D physics engine to calculate response to collisions, etc. I have a few 3D assets for which I'd like to be able to automatically generate a hitbox by 'slicing' the 3D mesh with the X-Y plane and creating a polygon from the resultant edges. Google is failing me on this one (and not much helpful material on SO either). Suggestions?

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  • 'Fixed' for loop - what is more efficient?

    - by pimvdb
    I'm creating a tic-tac-toe game, and one of the functions has to iterate through each of the 9 fields (tic-tac-toe is played on a 3x3 grid). I was wondering what is more efficient (which one is perhaps faster, or what is the preferred way of scripting in such situation) - using two for nested loops like this: for(var i=0; i<3; i++) { for(var j=0; j<3; j++) { checkField(i, j); } } or hard-coding it like this: checkField(0, 0); checkField(0, 1); checkField(0, 2); checkField(1, 0); checkField(1, 1); checkField(1, 2); checkField(2, 0); checkField(2, 1); checkField(2, 2); As there are only 9 combinations, it would be perhaps overkill to use two nested for loops, but then again this is clearer to read. The for loop, however, will increment variables and check whether i and j are smaller than 3 every time as well. In this example, the time saving at least might be negligible, but what is the preferred way of coding in this case? Thanks.

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  • Lexographical sorting problem

    - by Shawn Mclean
    I'm doing a problem that says concatenate the words to generate the lexicographically lowest possible string. from a competition. Take for example this string: jibw ji jp bw jibw The actual output turns out to be: bw jibw jibw ji jp When I do sorting on this, I get: bw ji jibw jibw jp. Does this mean that this is not sorting? If it is sorting, does lexicographic sorting take into consideration pushing the shorter strings to the back or something? I've been doing some reading on lexigographical order and I dont see any point or scenarios on which this is used, do you have any?

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  • All Permutations of a string when corresponding characters are not in the same place

    - by r20rock
    I need all possible permutations of a given string such that no character should remain at the same place as in the input string. Eg. : for input "ask" Output: all possible permutaions like "ksa", "kas"... such that 'a' is not in the 1st position , 's' is not in the 2nd positions and so on... in any permutation. I only need the count of such possible permutations I can do this by generating all permutations and filtering them but I need a very efficient way of doing this. All characters in the string are "UNIQUE" Preferred language C++.

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  • Pecking order of pigeons?

    - by sc_ray
    I was going though problems on graph theory posted by Prof. Ericksson from my alma-mater and came across this rather unique question about pigeons and their innate tendency to form pecking orders. The question goes as follows: Whenever groups of pigeons gather, they instinctively establish a pecking order. For any pair of pigeons, one pigeon always pecks the other, driving it away from food or potential mates. The same pair of pigeons always chooses the same pecking order, even after years of separation, no matter what other pigeons are around. Surprisingly, the overall pecking order can contain cycles—for example, pigeon A pecks pigeon B, which pecks pigeon C, which pecks pigeon A. Prove that any finite set of pigeons can be arranged in a row from left to right so that every pigeon pecks the pigeon immediately to its left. Since this is a question on Graph theory, the first things that crossed my mind that is this just asking for a topological sort of a graphs of relationships(relationships being the pecking order). What made this a little more complex was the fact that there can be cyclic relationships between the pigeons. If we have a cyclic dependency as follows: A-B-C-A where A pecks on B,B pecks on C and C goes back and pecks on A If we represent it in the way suggested by the problem, we have something as follows: C B A But the above given row ordering does not factor in the pecking order between C and A. I had another idea of solving it by mathematical induction where the base case is for two pigeons arranged according to their pecking order, assuming the pecking order arrangement is valid for n pigeons and then proving it to be true for n+1 pigeons. I am not sure if I am going down the wrong track here. Some insights into how I should be analyzing this problem will be helpful. Thanks

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  • Managed code (C#) vs Matlabs and C++ for speed

    - by dotnetdev
    Hi, I am about to start developing an edge detection system (once I've read through a couple of books, which I'm doing so at good speed), but one thing I am wondering is the speed of an app like Matlabs (which can compile code to C++) vs AFORGE.NET for edge detecton. Is unmanaged code generally faster? Thanks

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  • Typecasting a floating value or using the math.h floor* functions?

    - by nobody
    Hi, I am coding up an implementation of Interpolation Search in C. The question is actually rather simple, I need to use the floating operations to do linear interpolation to find the correct index which will eventually be an integer result. In particular my probe index is: t = i + floor((((k-low)/(high-low)) * (j-i))); where, i,j,k,t are unsigned ints, and high,low are doubles. Would this be equivalent to: t = i + (unsigned int)(((k-low)/(high-low)) * (j-i)); Is there any reason I would actually want to use math.h floor* functions over just a simple (int) typecast?

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  • How do we achieve "substring-match" under O(n) time?

    - by Pacerier
    I have an assignment that requires reading a huge file of random inputs, for example: Adana Izmir Adnan Menderes Apt Addis Ababa Aden ADIYAMAN ALDAN Amman Marka Intl Airport Adak Island Adelaide Airport ANURADHAPURA Kodiak Apt DALLAS/ADDISON Ardabil ANDREWS AFB etc.. If I specify a search term, the program is supposed to find the lines whereby a substring occurs. For example, if the search term is "uradha", the program is supposed to show ANURADHAPURA. If the search term is "airport", the program is supposed to show Amman Marka Intl Airport, Adelaide Airport A quote from the assignment specs: "You are to program this application taking efficiency into account as though large amounts of data and processing is involved.." I could easily achieve this functionality using a loop but the performance would be O(n). I was thinking of using a trie but it seems to only work if the substring starts from index 0. I was wondering what solutions are there which gives a performance better than O(n)?

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  • What is the better approach to find if a given set is a perfect subset of a set - If given subset is

    - by Microkernel
    Hi guys, What is the best approach to find if a given set(unsorted) is a perfect subset of a main set. I got to do some validation in my program where I got to compare the clients request set with the registered internal capability set. I thought of doing by having internal capability set sorted(will not change once registered) and do Binary search for each element in the client's request set. Is it the best I could get? I suspected that there might be better approach. Any idea? Regards, Microkernel

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  • sorting a doubly linked list with merge sort.

    - by user329820
    Hi I have found this code in the internet and it was for arrays ,I want to change it for doubly linked list(instead of index we should use pointer) would you please help me that how can i change merge method(I have changed sort method by myself) also this is not my home work ,I love working with linked list!! public class MergeSort { private DoublyLinkedList LocalDoublyLinkedList; public MergeSort(DoublyLinkedList list) { LocalDoublyLinkedList = list; } public void sort() { if (LocalDoublyLinkedList.size() <= 1) { return; } DoublyLinkedList listOne = new DoublyLinkedList(); DoublyLinkedList listTwo = new DoublyLinkedList(); for (int x = 0; x < (LocalDoublyLinkedList.size() / 2); x++) { listOne.add(x, LocalDoublyLinkedList.getValue(x)); } for (int x = (LocalDoublyLinkedList.size() / 2) + 1; x < LocalDoublyLinkedList.size`(); x++) {` listTwo.add(x, LocalDoublyLinkedList.getValue(x)); } //Split the DoublyLinkedList again MergeSort sort1 = new MergeSort(listOne); MergeSort sort2 = new MergeSort(listTwo); sort1.sort(); sort2.sort(); merge(listOne, listTwo); } private void merge(DoublyLinkedList a, DoublyLinkedList b) { int x = 0; int y = 0; int z = 0; while (x < first.length && y < second.length) { if (first[x] < second[y]) { a[z] = first[x]; x++; } else { a[z] = second[y]; y++; } z++; } //copy remaining elements to the tail of a[]; for (int i = x; i < first.length; i++) { a[z] = first[i]; z++; } for (int i = y; i < second.length; i++) { a[z] = second[i]; z++; } } }

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  • Pointer-based binary heap implementation

    - by Derek Chiang
    Is it even possible to implement a binary heap using pointers rather than an array? I have searched around the internet (including SO) and no answer can be found. The main problem here is that, how do you keep track of the last pointer? When you insert X into the heap, you place X at the last pointer and then bubble it up. Now, where does the last pointer point to? And also, what happens when you want to remove the root? You exchange the root with the last element, and then bubble the new root down. Now, how do you know what's the new "last element" that you need when you remove root again?

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  • Removing elements from heap

    - by user193138
    I made a heap. I am curious if there's something subtley wrong with my remove function: int Heap::remove() { if (n == 0) exit(1); int temp = arr[0]; arr[0] = arr[--n]; heapDown(0); arr[n] = 0; return temp; } void Heap::heapDown(int i) { int l = left(i); int r = right(i); // comparing parent to left/right child // each has an inner if to handle if the first swap causes a second swap // ie 1 -> 3 -> 5 // 3 5 1 5 1 3 if (l < n && arr[i] < arr[l]) { swap(arr[i], arr[l]); heapDown(l); if (r < n && arr[i] < arr[r]) { swap(arr[i], arr[r]); heapDown(r); } } else if (r < n && arr[i] < arr[r]) { swap(arr[i], arr[r]); heapDown(r); if (l < n && arr[i] < arr[l]) { swap(arr[i], arr[l]); heapDown(l); } } } Here's my output i1i2i3i4i5i6i7 p Active heap: 7 4 6 1 3 2 5 r Removed 7 r Removed 6 p Active heap: 5 3 4 1 2 Here's my teacher's sample output: p Active heap : 7 4 6 1 3 2 5 r Removed 7 r Removed 6 p Active heap : 5 4 2 1 3 s Heapsorted : 1 2 3 4 5 While our outputs are completely different, I do seem to hold maxheap principle of having everything left oriented and for all nodes parent child(in every case I tried). I try to do algs like this from scratch, so maybe I'm just doing something really weird and wrong (I would only consider it "wrong" if it's O(lg n), as removes are intended to be for heaps). Is there anything in particular "wrong" about my remove? Thanks, http://ideone.com/PPh4eQ

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  • Is there a standard pattern for scanning a job table executing some actions?

    - by Howiecamp
    (I realize that my title is poor. If after reading the question you have an improvement in mind, please either edit it or tell me and I'll change it.) I have the relatively common scenario of a job table which has 1 row for some thing that needs to be done. For example, it could be a list of emails to be sent. The table looks something like this: ID Completed TimeCompleted anything else... ---- --------- ------------- ---------------- 1 No blabla 2 No blabla 3 Yes 01:04:22 ... I'm looking either for a standard practice/pattern (or code - C#/SQL Server preferred) for periodically "scanning" (I use the term "scanning" very loosely) this table, finding the not-completed items, doing the action and then marking them completed once done successfully. In addition to the basic process for accomplishing the above, I'm considering the following requirements: I'd like some means of "scaling linearly", e.g. running multiple "worker processes" simultaneously or threading or whatever. (Just a specific technical thought - I'm assuming that as a result of this requirement, I need some method of marking an item as "in progress" to avoid attempting the action multiple times.) Each item in the table should only be executed once. Some other thoughts: I'm not particularly concerned with the implementation being done in the database (e.g. in T-SQL or PL/SQL code) vs. some external program code (e.g. a standalone executable or some action triggered by a web page) which is executed against the database Whether the "doing the action" part is done synchronously or asynchronously is not something I'm considering as part of this question.

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  • PHP Modify Array

    - by Ozzy
    Hi all, I have the following array: array(a, a, a, b, b, c, c, c, c, d, d); When I loop through it and echo it, the result is: a a a b b c c c c d d How ever I want to echo it in such a way that it displays: a b c d a b c d a c c Here is the array in a grid to better explain what im trying to achieve Current a a a b b c c c c d d What im tryin to do a b c d a b c d a c c How would I do this?

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