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  • Point covering problem

    - by Sean
    I recently had this problem on a test: given a set of points m (all on the x-axis) and a set n of lines with endpoints [l, r] (again on the x-axis), find the minimum subset of n such that all points are covered by a line. Prove that your solution always finds the minimum subset. The algorithm I wrote for it was something to the effect of: (say lines are stored as arrays with the left endpoint in position 0 and the right in position 1) algorithm coverPoints(set[] m, set[][] n): chosenLines = [] while m is not empty: minX = min(m) bestLine = n[0] for i=1 to length of n: if n[i][0] <= m and n[i][1] > bestLine[1] then bestLine = n[i] add bestLine to chosenLines for i=0 to length of m: if m <= bestLine[1] then delete m[i] from m return chosenLines I'm just not sure if this always finds the minimum solution. It's a simple greedy algorithm so my gut tells me it won't, but one of my friends who is much better than me at this says that for this problem a greedy algorithm like this always finds the minimal solution. For proving mine always finds the minimal solution I did a very hand wavy proof by contradiction where I made an assumption that probably isn't true at all. I forget exactly what I did. If this isn't a minimal solution, is there a way to do it in less than something like O(n!) time? Thanks

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  • Function Returning Negative Value

    - by Geowil
    I still have not run it through enough tests however for some reason, using certain non-negative values, this function will sometimes pass back a negative value. I have done a lot of manual testing in calculator with different values but I have yet to have it display this same behavior. I was wondering if someone would take a look at see if I am missing something. float calcPop(int popRand1, int popRand2, int popRand3, float pERand, float pSRand) { return ((((((23000 * popRand1) * popRand2) * pERand) * pSRand) * popRand3) / 8); } The variables are all contain randomly generated values: popRand1: between 1 and 30 popRand2: between 10 and 30 popRand3: between 50 and 100 pSRand: between 1 and 1000 pERand: between 1.0f and 5500.0f which is then multiplied by 0.001f before being passed to the function above Edit: Alright so after following the execution a bit more closely it is not the fault of this function directly. It produces an infinitely positive float which then flips negative when I use this code later on: pPMax = (int)pPStore; pPStore is a float that holds popCalc's return. So the question now is, how do I stop the formula from doing this? Testing even with very high values in Calculator has never displayed this behavior. Is there something in how the compiler processes the order of operations that is causing this or are my values simply just going too high? If the later I could just increase the division to 16 I think.

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  • Display image at point using jQuery

    - by Chris
    I have an image with a click event handler that captures the location where you clicked. $("#image").click(function(e) { var x = e.pageX - $(this).offset().left; var y = e.pageY - $(this).offset().top; }); I want it so that when the image is clicked an image appears at that location on top of the image. How do I do this?

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  • C# ? Can anyone explain the strange behaviour?

    - by partizan
    Hi, guys. Here is the example with comments: class Program { // first version of structure public struct D1 { public double d; public int f; } // during some changes in code then we got D2 from D1 // Field f type became double while it was int before public struct D2 { public double d; public double f; } static void Main(string[] args) { // Scenario with the first version D1 a = new D1(); D1 b = new D1(); a.f = b.f = 1; a.d = 0.0; b.d = -0.0; bool r1 = a.Equals(b); // gives true, all is ok // The same scenario with the new one D2 c = new D2(); D2 d = new D2(); c.f = d.f = 1; c.d = 0.0; d.d = -0.0; bool r2 = c.Equals(d); // false, oops! this is not the result i've expected for } } So, what do you think about this?

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  • Problem with Precision floating point operation in C

    - by Microkernel
    Hi Guys, For one of my course project I started implementing "Naive Bayesian classifier" in C. My project is to implement a document classifier application (especially Spam) using huge training data. Now I have problem implementing the algorithm because of the limitations in the C's datatype. ( Algorithm I am using is given here, http://en.wikipedia.org/wiki/Bayesian_spam_filtering ) PROBLEM STATEMENT: The algorithm involves taking each word in a document and calculating probability of it being spam word. If p1, p2 p3 .... pn are probabilities of word-1, 2, 3 ... n. The probability of doc being spam or not is calculated using Here, probability value can be very easily around 0.01. So even if I use datatype "double" my calculation will go for a toss. To confirm this I wrote a sample code given below. #define PROBABILITY_OF_UNLIKELY_SPAM_WORD (0.01) #define PROBABILITY_OF_MOSTLY_SPAM_WORD (0.99) int main() { int index; long double numerator = 1.0; long double denom1 = 1.0, denom2 = 1.0; long double doc_spam_prob; /* Simulating FEW unlikely spam words */ for(index = 0; index < 162; index++) { numerator = numerator*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom1 = denom1*(long double)(1 - PROBABILITY_OF_UNLIKELY_SPAM_WORD); } /* Simulating lot of mostly definite spam words */ for (index = 0; index < 1000; index++) { numerator = numerator*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom1 = denom1*(long double)(1- PROBABILITY_OF_MOSTLY_SPAM_WORD); } doc_spam_prob= (numerator/(denom1+denom2)); return 0; } I tried Float, double and even long double datatypes but still same problem. Hence, say in a 100K words document I am analyzing, if just 162 words are having 1% spam probability and remaining 99838 are conspicuously spam words, then still my app will say it as Not Spam doc because of Precision error (as numerator easily goes to ZERO)!!!. This is the first time I am hitting such issue. So how exactly should this problem be tackled?

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  • Pi/Infinite Numbers

    - by Ben Shelock
    I'm curious about infinite numbers in computing, in particular pi. For a computer to render a circle it would have to understand pi. But how can it if it is infinite? Am I looking too much into this? Would it just use a rounded value?

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  • Creating Synch Point In TFS Source Tree Development Cycle

    - by Rob G
    Our development cycle rarely requires a branch so we have what tfs appears to consider a single, never-ending development cycle. Our problem is that each build includes an ever increasing long "Generating list of changesets and updating work items" step that includes all changesets/work items back to day 1. What is the proper step that we need to perform to formally lock and label (wrong terms I'm sure) the source tree so that a new cycle of changesets and work items can begin. Thanks!

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  • Preoblem with Precision floating point operation in C

    - by Microkernel
    Hi Guys, For one of my course project I started implementing "Naive Bayesian classifier" in C. My project is to implement a document classifier application (especially Spam) using huge training data. Now I have problem implementing the algorithm because of the limitations in the C's datatype. ( Algorithm I am using is given here, http://en.wikipedia.org/wiki/Bayesian_spam_filtering ) PROBLEM STATEMENT: The algorithm involves taking each word in a document and calculating probability of it being spam word. If p1, p2 p3 .... pn are probabilities of word-1, 2, 3 ... n. The probability of doc being spam or not is calculated using Here, probability value can be very easily around 0.01. So even if I use datatype "double" my calculation will go for a toss. To confirm this I wrote a sample code given below. #define PROBABILITY_OF_UNLIKELY_SPAM_WORD (0.01) #define PROBABILITY_OF_MOSTLY_SPAM_WORD (0.99) int main() { int index; long double numerator = 1.0; long double denom1 = 1.0, denom2 = 1.0; long double doc_spam_prob; /* Simulating FEW unlikely spam words */ for(index = 0; index < 162; index++) { numerator = numerator*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_UNLIKELY_SPAM_WORD; denom1 = denom1*(long double)(1 - PROBABILITY_OF_UNLIKELY_SPAM_WORD); } /* Simulating lot of mostly definite spam words */ for (index = 0; index < 1000; index++) { numerator = numerator*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom2 = denom2*(long double)PROBABILITY_OF_MOSTLY_SPAM_WORD; denom1 = denom1*(long double)(1- PROBABILITY_OF_MOSTLY_SPAM_WORD); } doc_spam_prob= (numerator/(denom1+denom2)); return 0; } I tried Float, double and even long double datatypes but still same problem. Hence, say in a 100K words document I am analyzing, if just 162 words are having 1% spam probability and remaining 99838 are conspicuously spam words, then still my app will say it as Not Spam doc because of Precision error (as numerator easily goes to ZERO)!!!. This is the first time I am hitting such issue. So how exactly should this problem be tackled?

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  • PHP: Loop through text file and isolate lines which a specific "starting point"

    - by Mestika
    Hi everyone, I’m trying to reduce some editing time within some textfiles where there approximately are 10.000 lines of text, but I only need around 200 or some. The text file relies on a almost specific pattern but it deviates from time to time but my “focus” in order to select the right line to keep is, that the line always starts with: z3455 and then have a variable afterwards, e.g.: z3455 http://url.com/data1/data1.1/data1.3/ (342kb) I have an algorithm to capture the URL and its content but now I need some way to loop through the text file, deleting all lines except does that starts with z3455 and then “push” them together so they are listed underneath each other. I’ve tried different approaches for this in PHP but can’t seem to find a correct function. I can “isolate” a specific line number but when it deviates I can’t use this approach fully. I hope that someone can help me, either by providing the code or knocking me in the right direction to how I’ll solve this problem. Thanks in advance Sincerely - Mestika

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  • Freeing Java memory at a specific point in time

    - by Marcus
    Given this code, where we load a lot of data, write it to a file, and then run an exe.. void myMethod() { Map stuff = createMap(); //Consumes 250 MB memory File file = createFileInput(stuff); //Create input for exe runExectuable(file); //Run Windows exe } What is the best way to release the memory consumed by stuff prior to running the exe? We don't need this in memory any more as we have dumped the data to a file for input to the exe... Is the best method to just set stuff = null prior to runExecutable(file)?

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  • Neo4j+Gremlin : Trouble with T.gte and floating point node attributes

    - by letronje
    For a type of nodes in my graph, attribute values for an attribute(named 'some_count') is either missing or an integer or a float. I'm trying to write gremlin to filter these nodes based on minimum value for this attribute. I first verified that the values are indeed present by firing the following gremlin g.v(XXX)._().in('category').hasNot('some_count', T.eq, null).back(1).some_count Next, I tried filtering by exact value and that works and show me the matching nodes or gives an empty array if there is no match g.v(XXX)._().in('category').hasNot('some_count', T.eq, null).back(1).has('some_count', T.eq, 120000.0d) But the following query that uses the 'greater than or equal to' comparator doesn't work. g.v(XXX)._().in('category').hasNot('some_count', T.eq, null).back(1).has('some_count', T.gte, 1.0d) this returns nil (I'm querying via ruby/rails using Neo4j AR Adapter ) Instead of returning an empty array for no match, it returns a nil, which tells me something could be wrong with the query itself. I'm running neo4j community server 1.8. Is there a way I can ask Neo4j to log errors/queries, to see what could be going wrong ?

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  • Rounding issue when adding floats in python, is this normal?

    - by thepearson
    I just wanted to know if this behavior is expected. If so, can someone explain to me why. This has probably been answered elsewhere I can't seem to find it using Google. Probably not searching with the right terms. I am running Ubuntu 10.04. Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> var = 10.0 >>> var 10.0 >>> var + 5 15.0 >>> var + 5.1 15.1 >>> var + 5.2 15.199999999999999 >>>

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  • What is the point of function pointers?

    - by gramm
    Hi, I have trouble seing the utility of the function pointers. I guess it may be useful in some cases (they exist, after all), but I can't think of a case where it's better or unavoidable to use a function pointer. Could you give some example of good use of function pointers (in C or C++)? Many thanks :)

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  • jquery - sliding image group left and right (hiding the ones that are past a certain point)

    - by matthewsteiner
    So I'm not really sure how to go about doing this at all. I've got an anchor on the left with id="left" and one on the right with id="right". On the hover event, the image thumbnails should start sliding left or right. If there's not enough thumbnails, there should be no sliding. It can only fit 4 images in between the left and right anchors. How can I hide all anchors that are not in between the left and right anchors? I want the images to actually slowly move left or right, not just be sudden. Any ideas? I know how to bind the events and such just fine. I just don't really now how to get started with the image placement.

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  • Dividing a double with integer

    - by hardcoder
    I am facing an issue while dividing a double with an int. Code snippet is : double db = 10; int fac = 100; double res = db / fac; The value of res is 0.10000000000000001 instead of 0.10. Does anyone know what is the reason for this? I am using cc to compile the code.

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  • doing arithmetic upto two significant figures in Python?

    - by user248237
    I have two floats in Python that I'd like to subtract, i.e. v1 = float(value1) v2 = float(value2) diff = v1 - v2 I want "diff" to be computed upto two significant figures, that is compute it using %.2f of v1 and %.2f of v2. How can I do this? I know how to print v1 and v2 up to two decimals, but not how to do arithmetic like that. thanks.

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  • Codeigniter PHP - loading a view at an anchor point

    - by James Billings
    I have a form at the bottom of a long page, if a user fills out the form but it doesn't validate the page is reloaded in the typical codeigniter fashion: $this->load->view('template',$data); however because the form is way down at the bottom of the page I need the page to load down there like you do with HTML anchors. Does anyone know how to do this in codeigniter? I can't use the codeigniter redirect(); function because it loses the object and the validation errors are gone. Other frameworks I've used like Yii you can call the redirect function like: $this->redirect(); which solves the problem because you keep the object. I've tried using: $this->index() within the controller which works fine as a redirect but the validation errors are in another method which is where the current page is loaded from: $this->item($labs) but when I use this it get stuck in a loop Any ideas? I've seen this question a lot on the net but no clear answers. I'm researching using codeigniter "flash data" but think it's a bit overkill. cheers.

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  • [.NET] What's the point of MarshalByValue Object?

    - by smwikipedia
    Hi awesome! We know that MarshalByRef allow us to create an object in a different AppDomain and use a Proxy object to access it. And the behavior of that object is in a different context of the AppDomain where it actually lives in. Well this sounds faily reseaonable in the regard of isolation and safety. But why is there still MarshalByValue? MarshalByValue just leads to an newly deserialized object which is an exact copy of the object in a different AppDomain. If we need that object, why not just create it in the current AppDomain? Why bother to first create it in a different AppDomain and then get it back by MarshaoByValue? Many thanks.

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  • C# WTF? Can anyone explain the strange behaviour?

    - by partizan
    Hi, guys. Here is the example with comments: class Program { // first version of structure public struct D1 { public double d; public int f; } // during some changes in code then we got D2 from D1 // Field f type became double while it was int before public struct D2 { public double d; public double f; } static void Main(string[] args) { // Scenario with the first version D1 a = new D1(); D1 b = new D1(); a.f = b.f = 1; a.d = 0.0; b.d = -0.0; bool r1 = a.Equals(b); // gives true, all is ok // The same scenario with the new one D2 c = new D2(); D2 d = new D2(); c.f = d.f = 1; c.d = 0.0; d.d = -0.0; bool r2 = c.Equals(d); // false, oops! this is not the result i've expected for } } So, what do you think about this?

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  • int and float increment condition in for loop [on hold]

    - by Mazaya Jamil
    I am doing a program that involves integer and float number.Let say I want to calculate atx={1,1/2,2,3,4} and want to use for-loop. But I know the condition of increment for(x=1;x<=4;x++) as x++=x+1. I want to find the iteration at x={1,2,3,4} and at x={1/2}. But I do not have idea how to modify the for-loop statement; either to make the increment of 0.5 or 1. But if I set 0.5, I will get the answers for 5/2 and 7/2 instead.

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