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  • Encoding / Error Correction Challenge

    - by emi1faber
    Is it mathematically feasible to encode and initial 4 byte message into 8 bytes and if one of the 8 bytes is completely dropped and another is wrong to reconstruct the initial 4 byte message? There would be no way to retransmit nor would the location of the dropped byte be known. If one uses Reed Solomon error correction with 4 "parity" bytes tacked on to the end of the 4 "data" bytes, such as DDDDPPPP, and you end up with DDDEPPP (where E is an error) and a parity byte has been dropped, I don't believe there's a way to reconstruct the initial message (although correct me if I am wrong)... What about multiplying (or performing another mathematical operation) the initial 4 byte message by a constant, then utilizing properties of an inverse mathematical operation to determine what byte was dropped. Or, impose some constraints on the structure of the message so every other byte needs to be odd and the others need to be even. Alternatively, instead of bytes, it could also be 4 decimal digits encoded in some fashion into 8 decimal digits where errors could be detected & corrected under the same circumstances mentioned above - no retransmission and the location of the dropped byte is not known. I'm looking for any crazy ideas anyone might have... Any ideas out there?

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  • List all possible combinations of k integers between 1...n (n choose k)

    - by Asaf R
    Hi, Out of no particular reason I decided to look for an algorithm that produces all possible choices of k integers between 1...n, where the order amongst the k integer doesn't matter (the n choose k thingy). From the exact same reason, which is no reason at all, I also implemented it in C#. My question is: Do you see any mistake in my algorithm or code? And, more importantly, can you suggest a better algorithm? Please pay more attention to the algorithm than the code itself. It's not the prettiest code I've ever written, although do tell if you see an error. EDIT: Alogirthm explained - We hold k indices. This creates k nested for loops, where loop i's index is indices[i]. It simulates k for loops where indices[i+1] belongs to a loop nested within the loop of indices[i]. indices[i] runs from indices[i - 1] + 1 to n - k + i + 1. CODE: public class AllPossibleCombination { int n, k; int[] indices; List<int[]> combinations = null; public AllPossibleCombination(int n_, int k_) { if (n_ <= 0) { throw new ArgumentException("n_ must be in N+"); } if (k_ <= 0) { throw new ArgumentException("k_ must be in N+"); } if (k_ > n_) { throw new ArgumentException("k_ can be at most n_"); } n = n_; k = k_; indices = new int[k]; indices[0] = 1; } /// <summary> /// Returns all possible k combination of 0..n-1 /// </summary> /// <returns></returns> public List<int[]> GetCombinations() { if (combinations == null) { combinations = new List<int[]>(); Iterate(0); } return combinations; } private void Iterate(int ii) { // // Initialize // if (ii > 0) { indices[ii] = indices[ii - 1] + 1; } for (; indices[ii] <= (n - k + ii + 1); indices[ii]++) { if (ii < k - 1) { Iterate(ii + 1); } else { int[] combination = new int[k]; indices.CopyTo(combination, 0); combinations.Add(combination); } } } } I apologize for the long question, it might be fit for a blog post, but I do want the community's opinion here. Thanks, Asaf

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  • Can I use ido-completing-read instead of completing-read everywhere?

    - by haxney
    I'm a big fan of ido-mode, so much so that I would like to use it for things like describe-function or find-tag and so on, without having to write something like in "Can I get ido-mode-style completion for searching tags in Emacs?" for each one. Both (defalias completing-read ido-completing-read) and (setf 'completing-read 'ido-completing-read) don't work, at least partly because ido-completing-read calls completing-read in its body, so any simple redefinition would result in infinite recursion. In theory, it should be possible, since the first line of the docstring for ido-completing-read is "Ido replacement for the built-in completing-read." I've looked around a bit and can't seem to find anyone else who has attempted or succeeded at it. I realize that Icicles [2] probably provides something like this, and I may end up going with that anyway, but it is a bit more of a plunge than I care to take right now. Thanks for any help.

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  • Best fit curve for trend line

    - by Dave Jarvis
    Problem Constraints Size of the data set, but not the data itself, is known. Data set grows by one data point at a time. Trend line is graphed one data point at a time (using a spline/Bezier curve). Graphs The collage below shows data sets with reasonably accurate trend lines: The graphs are: Upper-left. By hour, with ~24 data points. Upper-right. By day for one year, with ~365 data points. Lower-left. By week for one year, with ~52 data points. Lower-right. By month for one year, with ~12 data points. User Inputs The user can select: the type of time series (hourly, daily, monthly, quarterly, annual); and the start and end dates for the time series. For example, the user could select a daily report for 30 days in June. Trend Weight To calculate the window size (i.e., the number of data points to average when calculating the trend line), the following expression is used: data points / trend weight Where data points is derived from user inputs and trend weight is 6.4. Even though a trend weight of 6.4 produces good fits, it is rather arbitrary, and might not be appropriate for different user inputs. Question How should trend weight be calculated given the constraints of this problem?

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  • Orcad / Matlab: How to plot the roots of a polynomial

    - by Tom
    Hi everyone, Im trying to plot the roots of a polynomial, and i just cant get it. First i create my polynomial p5 = [1 0 0 0 0 -1] %x^5 - 1 r5 = roots(p5) stem (p5) Im using the stem function, but I would like to remove the stems, and just get the circle around the roots. Is this possible, is stem the right command? Thanks in advance, PS: This is not homework, but very close, will tag it if requested.

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  • An implementation of Sharir's or Aurenhammer's deterministic algorithm for calculating the intersect

    - by RGrey
    The problem of finding the intersection/union of 'N' discs/circles on a flat plane was first proposed by M. I. Shamos in his 1978 thesis: Shamos, M. I. “Computational Geometry” Ph.D. thesis, Yale Univ., New Haven, CT 1978. Since then, in 1985, Micha Sharir presented an O(n log2n) time and O(n) space deterministic algorithm for the disc intersection/union problem (based on modified Voronoi diagrams): Sharir, M. Intersection and closest-pair problems for a set of planar discs. SIAM .J Comput. 14 (1985), pp. 448-468. In 1988, Franz Aurenhammer presented a more efficient O(n log n) time and O(n) space algorithm for circle intersection/union using power diagrams (generalizations of Voronoi diagrams): Aurenhammer, F. Improved algorithms for discs and balls using power diagrams. Journal of Algorithms 9 (1985), pp. 151-161. Earlier in 1983, Paul G. Spirakis also presented an O(n^2) time deterministic algorithm, and an O(n) probabilistic algorithm: Spirakis, P.G. Very Fast Algorithms for the Area of the Union of Many Circles. Rep. 98, Dept. Comput. Sci., Courant Institute, New York University, 1983. I've been searching for any implementations of the algorithms above, focusing on computational geometry packages, and I haven't found anything yet. As neither appear trivial to put into practice, it would be really neat if someone could point me in the right direction!

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  • Touch coordinates in iPhone landscape mode app

    - by gok
    I am trying to make this landscape only iphone app. I only use this code for this purpose: - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { return (interfaceOrientation == UIInterfaceOrientationLandscapeRight); } However when I click clip subviews checkbox from interface builder, the view is clipped from the middle. I also don't receive any touch events from outside of view bounds obviously. - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { CGPoint fingerPos = [[touches anyObject] locationInView:self.view]; NSLog(@"%f %f",fingerPos.x,fingerPos.y); } only prints for coordinates between 20 and 320 for X. But Y works fine. When i try to modify bounds by hand, everything works fine; View is positioned and shown correctly, printed coordinates are correct, I receive touch from all of the screen except between 0 and 20 for X. So Left side of the screen is unresponsive to touch events for only 20 pixels. Code I use to modify bounds: self.view.bounds = CGRectMake(-180.0f, 0.0f, 680.0f, 480.0f); What might be causing this? Weird!

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  • read url in binary mode in java

    - by Andrew Zawok
    In java I need to read a binary file from a site and write it to a disk file. This example http://java.sun.com/docs/books/tutorial/networking/urls/readingURL.html could read webpages succesfully, but when I try to read a binary file from my localhost server and write it to a disk file the contents change, corrupting the binary file. Using fc I see that 0x90 is changed to 0x3F and other changes. How do I acess the binary files (read url and write to file) without java or anything else changing ANY characters, like doing any newline conversions or character conversions or anything else, simply reading input url and writing it out as a file.

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  • probability and relative frequency

    - by Alexandru
    If I use relative frequency to estimate the probability of an event, how good is my estimate based on the number of experiments? Is standard deviation a good measure? A paper/link/online book would be perfect. http://en.wikipedia.org/wiki/Frequentist

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  • Percentage calculation around 0.5 (0.4 = -20% and 0.6 = +20%)

    - by Micheal
    I'm in a strange situation where I have a value of 0.5 and I want to convert the values from 0.5 to 1 to be a percentage and from 0.5 to 0 to be a negative percentage. As it says in the title 0.4 should be -20%, 0.3 should be -40% and 0.1 should be -80%. I'm sure this is a simple problem, but my mind is just refusing to figure it out :) Can anyone help? :)

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  • java jama array problem

    - by agazerboy
    Hi All, I asked a question before but duffymo said it is not clear so i am going to post it again here. I am using Jama api for SVD calculation. I know very well about jama and SVD. Jama does not work if your column are more than rows. I have this situation. What should I do?? any help? I can't transpose the matrix too as it can produce wrong results. Thanks. P.S: I am calculating LSI with the help of jama. I am going like column(docs) and rows ( terms )

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  • how do you hook up a callback event when using jquery ui tabs in ajax mode

    - by ooo
    Here is my html code using jquery ui tabs. As you can see, for the third tab, i am loading remotely through a feature built into jquery ui tabs where you just put a link in and it retrieves it remotely. My one open issue is that i would like a callback method when its done retrieving /Tracker/DailyTracker. is this possible? <div id="tabs"> <ul> <li><a href="#tab1">1</a></li> <li><a href="#tab2">2</a></li> <li><a href="/Tracker/DailyTracker"><span>3</span></a></li>

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  • Finding subsets that can be completed to tuples without duplicates

    - by Jules
    We have a collection of sets A_1,..,A_n. The goal is to find new sets for each of the old sets. newA_i = {a_i in A_i such that there exist (a_1,..,a_n) in (A1,..,An) with no a_k = a_j for all k and j} So in words this says that we remove all the elements from A_i that can't be used to form a tuple (a_1,..a_n) from the sets (A_1,..,A_n) such that the tuple doesn't contain duplicates. My question is how to compute these new sets quickly. If you just implement this definition by generating all possible v's this will take exponential time. Do you know a better algorithm? Edit: here's an example. Take A_1 = {1,2,3,4} A_2 = {2}. Now the new sets look like this: newA_1 = {1,3,4} newA_2 = {2} The 2 has been removed from A_1 because if you choose it the tuple will always be (2,2) which is invalid because it contains duplicates. On the other hand 1,3,4 are valid because (1,2), (3,2) and (4,2) are valid tuples. Another example: A_1 = {1,2,3} A_2 = {1,4,5} A_3 = {2,4,5} A_4 = {1,2,3} A_5 = {1,2,3} Now the new sets are: newA_1 = {1,2,3} newA_2 = {4,5} newA_3 = {4,5} newA_4 = {1,2,3} newA_5 = {1,2,3} The 1 and 2 are removed from sets 2 and 3 because if you choose the 1 or 2 from these sets you'll only have 2 values left for sets 1, 4 and 5, so you will always have duplicates in tuples that look like (_,1,_,_,_) or like (_,_,2,_,_).

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  • Laplacian of Gaussian

    - by Don
    I am having trouble implementing a LoG kernel. I am trying to implement 9x9 kernal with theta = 1.4 as shown in this link http://homepages.inf.ed.ac.uk/rbf/HIPR2/log.htm. However, I am having difficulty with the formula itself.For whatever values I input into the formula, I don't get any of the values in a 9x9 LoG kernel with theta = 1. 4. If someone can provide an example of how they got one of the big values ie -40 or -23, or the code to implement it, It'd be greatly appreciated. Thank you

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  • How to stop scrolling in a virtual (LVS_OWNERDATA) listview in LVS_REPORT mode when using changing t

    - by David L Morris
    Win32 Virtual listviews (LVS_REPORT view) created with the LVS_OWNERDATA style are supposed not to scroll when LVSICF_NOSCROLL is used in the LVM_SETITEMCOUNT message or ListView_SetItemCountEx macro, according the MSDN documentation. However, this doesn't seem work, and the list-view scrolls regardless of the use of LVSICF_NOSCROLL. In these sorts of cases, 99% of the time it is something I have done incorrectly or overlooked. But, I've now run out of options. Have I missed something?

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  • Detecting Asymptotes in a Graph

    - by nasufara
    I am creating a graphing calculator in Java as a project for my programming class. There are two main components to this calculator: the graph itself, which draws the line(s), and the equation evaluator, which takes in an equation as a String and... well, evaluates it. To create the line, I create a Path2D.Double instance, and loop through the points on the line. To do this, I calculate as many points as the graph is wide (e.g. if the graph itself is 500px wide, I calculate 500 points), and then scale it to the window of the graph. Now, this works perfectly for most any line. However, it does not when dealing with asymptotes. If, when calculating points, the graph encounters a domain error (such as 1/0), the graph closes the shape in the Path2D.Double instance and starts a new line, so that the line looks mathematically correct. Example: However, because of the way it scales, sometimes it is rendered correctly, sometimes it isn't. When it isn't, the actual asymptotic line is shown, because within those 500 points, it skipped over x = 2.0 in the equation 1 / (x-2), and only did x = 1.98 and x = 2.04, which are perfectly valid in that equation. Example: In that case, I increased the window on the left and right one unit each. My question is: Is there a way to deal with asymptotes using this method of scaling so that the resulting line looks mathematically correct? I myself have thought of implementing a binary search-esque method, where, if it finds that it calculates one point, and then the next point is wildly far away from the last point, it searches in between those points for a domain error. I had trouble figuring out how to make it work in practice, however. Thank you for any help you may give!

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  • h2 (embedded mode ) database files problem

    - by aeter
    There is a h2-database file in my src directory (Java, Eclipse): h2test.db The problem: starting the h2.jar from the command line (and thus the h2 browser interface on port 8082), I have created 2 tables, 'test1' and 'test2' in h2test.db and I have put some data in them; when trying to access them from java code (JDBC), it throws me "table not found exception". A "show tables" from the java code shows a resultset with 0 rows. Also, when creating a new table ('newtest') from the java code (CREATE TABLE ... etc), I cannot see it when starting the h2.jar browser interface afterwards; just the other two tables ('test1' and 'test2') are shown (but then the newly created table 'newtest' is accessible from the java code). I'm inexperienced with embedded databases; I believe I'm doing something fundamentally wrong here. My assumption is, that I'm accessing the same file - once from the java app, and once from the h2 console-browser interface. I cannot seem to understand it, what am I doing wrong here?

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  • 3D World to Local transformation

    - by Bill Kotsias
    Hello. I am having a real headache trying to set a node's local position to match a given world position. I was given a solution but, AFAICS, it only takes into account orientation and position but NOT scaling : node_new_local_position = node_parent.derivedOrientation().Inverse() * ( world_position_to_match - node_parent.derivedPosition() ); The node in question is a child of node_parent; node_parent local and derived properties (orientation, position and scaling) are known, as well as its full matrix transform. All the positions are 3d vectors; the orientation is a quaternion; the full transform is a 4x4 matrix. Could someone please help me to modify the solution to support scaling in the node hierarchy? Many thanks in advance, Bill

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  • emacs: force ido-mode to forget history...

    - by Stephen
    Hi, I wonder if I can keep ido from not remembering my history and only show completions for files that are in the current directory when I am searching for a file. I understand that this history feature is useful at times, but I often end up editing the incorrect file because I think I am editing file called 'abc.txt' in the current directory but in fact I am editing the file by the same name in another one that I previously visited (often happens when there is not an 'abc.txt' in the current directory, as I mistakenly assume). From reading the ido.el file I thought to set in my .emacs file (also evaluated these expressions in running emacs instance): (custom-set-variables '(ido-enable-last-directory-history nil) '(ido-record-commands nil) ) and deleted a file called .ido.last in ~/, but still it remembers some previous files I've visited before making these changes. How can I purge my previous history, and I am not entirely sure what the difference between the two variables above are but seems to have done the trick to keep ido from remembering files I visit in the future? Thanks for your help!

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  • Algorithm to fill slots

    - by Peter Lang
    I am searching for an algorithm to fill several slots, which are already filled to some level. The current levels and the available quantity to fill are known Resulting levels should be as equal as possible, but existing level cannot be reduced Slots are filled from left to right, so left slots get higher level if equal level is impossible       The image above shows six examples, each column represents a slot. The grey area is already filled, the blue are is the expected position of the new elements. I could iterate through my slots and increase the quantity on the lowest slot by 1 until the available quantity is consumed, but I wonder about how to actually calculate the new filling levels. I am going to implement this with SQL/PL/SQL, other code is just as welcome though :)

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