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  • SQL query to get field value distribution (mode)

    - by Bryan Lewis
    I have a table of over 1 million test score records that basically have a unique score_ID, a subject_ID and a score given by a person. The score range for most subjects is 0-3, but some have a range of 0-4. There are about 25 possible subjects. I need to produce a score distribution report which looks like: subject_ID 0 1 2 3 4 ---------- --- --- --- --- --- 1 967 576 856 234 2 576 947 847 987 324 . . So it groups the data by subject_ID, then shows how many times a specific score value was given within that subject. Any SQL pointers to generate this would be greatly appreciated.

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  • How to implement a grapher in C#

    - by iansinke
    So I'm writing a graphing calculator. So far I have a semi-functional grapher, however, I'm having a hard time getting a good balance between accurate graphs and smooth looking curves. The current implementation (semi-pseudo-code) looks something like this: for (float i = GraphXMin; i <= GraphXMax; i++) { PointF P = new PointF(i, EvaluateFunction(Function, i) ListOfPoints.Add(P) } Graphics.DrawCurve(ListOfPoints) The problem with this is since it only adds a point at every integer value, graphs end up distorted when their turning points don't fall on integers (e.g. sin(x)^2). I tried incrementing i by something smaller (like 0.1), which works, but the graph looks very rough. I am using C# and GDI+. I have SmoothingMethod set to AntiAlias, so that's not the problem, as you can see from the first graph. Is there some sort of issue with drawing curves with a lot of points? Should the points perhaps be positioned exactly on pixels? I'm sure some of you have worked on something very similar before, so any suggestions? While you're at it, do you have any suggestions for graphing functions with asymptotes? e.g. 1/x^2 P.S. I'm not looking for a library that does all this - I want to write it myself.

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  • All non-prime factorings

    - by Tony Veijalainen
    Let's say we have numbers factors, for example 1260: >>> factors(1260) [2, 2, 3, 3, 5, 7] Which would be best way to do in Python combinations with every subproduct possible from these numbers, ie all factorings, not only prime factoring, with sum of factors less than max_sum? If I do combinations from the prime factors, I have to refactor remaining part of the product as I do not know the remaining part not in combination. Example results would be: [4, 3, 3, 5, 7] (one replacement) [3, 6, 14, 5] (two replacements)

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  • Drawing Directed Acyclic Graphs: Using DAG property to improve layout/edge routing?

    - by Robert Fraser
    Hi, Laying out the verticies in a DAG in a tree form (i.e. verticies with no in-edges on top, verticies dependent only on those on the next level, etc.) is rather simple. However, is there a simple algorithm to do this that minimizes edge crossing? (For some graphs, it may be impossible to completely eliminate edge crossing.) A picture says a thousand words, so is there an algorithm that would suggest: instead of:

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  • Faster way to compare two sets of points in N-dimensional space?

    - by Amit
    List1 contains a high number (~7^10) of N-dimensional points (N <=10), List2 contains the same or fewer number of N-dimensional points (N <=10). My task is this: I want to check which point in List2 is closest (euclidean distance) to a point in List1 for every point in List1 and subsequently perform some operation on it. I have been doing it the simple- the nested loop way when I didn't have more than 50 points in List1, but with 7^10 points, this obviously takes up a lot of time. What is the fastest way to do this? Any concepts from Computational Geometry might help?

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  • simple rank formula

    - by Graham
    I'm looking for a mathmatical ranking formula. Sample is 2008 2009 2010 A 5 6 4 B 6 7 5 C 7 8 2 I want to add a rank column for each period code field rank 2008 2009 2010 2008 2009 2010 B 6 7 5 2 1 1 A 5 6 4 3 2 2 C 7 2 2 1 3 3 please do not reply with methods that loop thru the rows and columns, incrementing the rank value as it goes, that's easy. I'm looking for a formula much like finding the percent total (item / total). I know i've seen this before but an havning a tough time locating it. Thanks in advance!

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  • Fastest way to find the rotation of a vector

    - by kriss
    I have two 2D vectors, say u and v, defined by cartesian coordinates. Imagine that vectors are needles of a clock. I'm looking for the fastest way to find out, using python, if v is after or before u (or in other words find out in wich half plane is v, regarding to position of u). For the purpose of the problem if vectors are aligned answer should be before. It seems easy using some trigonometry, but I believe there should be a faster way using coordinates only. My test case: def after(u, v): """code here""" after((4,2), (6, 1)) : True after((4,2), (3, 3)) : False after((4,2), (2, 1)) : False after((4,2), (3, -3)) : True after((4,2), (-2, -5)) : True after((4,2), (-4, -2)) : False

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  • Why isnt int pow(int base, int exponent) in the standard C++ libraries?

    - by Dan O
    I feel like I must just be unable to find it. Is there any reason that the c++ pow function does not implement the "power" function for anything except floats and doubles? I know the implementation is trivial, I just feel like I'm doing work that should be in a standard library. A robust power function (ie handles overflow in some consistent, explicit way) is not fun to write.

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  • 6^x = 5 equation, how to solve it?

    - by Tom
    If it would be 6^x = 1 or 6^x = 6 or 6^x = 36 it would be extremely easy, but how to solve this equation: 6^x = 5 I don't need an answer, I want to find out how to solve equations like this one, I need solution. Thanks.

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  • Android debug mode not working waiting for device

    - by Blue42
    I'm trying to get my android phone working to run apps from inside an IDE. Got it working on windows no problem, currently working in fedora (18) a lot though so wanted to get it working with that. Got IntelliJ and android sdk installed, problem is when I try to run the default hello world app it wont work it just says waiting for device.. Ran adb devices got List of devices attached ???????????? no permissions Leads me to believe the driver isn't installed? Phone I'm using is a HTC Sensation. Does anyone know what I can do to try and resolve it? The HTC web page doesn't offer me drivers to install. Also noticed in /etc/udev/rules.d/..android.rules there is nothing about Sensation. Seems it recognises my nexus 7 though.. Edit: Tried my nexus.. got List of devices attached 901839238298923 offline So it doesn't even work with that.. confusing.. Any help would be appreciated. Thanks, B

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  • Android: Find coordinates of a certain point X meters from my location moving towards the point I am

    - by Aidan
    Hi Guys, I'm constructing a geolocation based application and I'm trying to figure out a way to make my application realise when a user is facing the direction of the given location (a particular long / lat co-ord). I've done some Googling and checked the SDK but can't really find anything for such a thing. Does anyone know of a way? Example. Point A = Phones current location. Point B = A's orientation in relation to true north + 45 + max distance towards the direction your facing, Point C = A's orientation in relation to true north - 45 + max distance towards the direction your facing. So now you have a triangle constructed. pretty schweet huh? yeah.. I think so.. So now that I have my fancy Triangle I use something called Barycentric Coordinates ( http://en.wikipedia.org/wiki/Barycentric_coordinates_(mathematics) ). This will allow me to test another point and see if it is in the triangle. If it is, it means we're facing it AND it's within the right distance. So it should be displayed on screen. If I'm facing 90 degrees from true north. The distance it travels should be that direction. 90 degrees from true north. It should not be 100 degrees or something from true north! But the problem is I haven't yet figured out how I make the device realise it must go "out" the direction it is facing.

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  • C++ integer floor function

    - by Thomas
    I want to implement greatest integer function. int x = 5/3; My question is with greater numbers could there be a loss of precision as 5/3 would produce a double? EDIT: Greatest integer function is integer less than or equal to X. Example: 4.5 = 4 4 = 4 3.2 = 3 3 = 3 What I want to know is 5/3 going to produce a double? Because if so I will have loss of precision when converting to int. Hope this makes sense. RE-EDIT: What OP calls 'greatest integer' most of us call 'floor'.

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  • Linear Interpolation. How to implement this algorithm in C ? (Python version is given)

    - by psihodelia
    There exists one very good linear interpolation method. It performs linear interpolation requiring at most one multiply per output sample. I found its description in a third edition of Understanding DSP by Lyons. This method involves a special hold buffer. Given a number of samples to be inserted between any two input samples, it produces output points using linear interpolation. Here, I have rewritten this algorithm using Python: temp1, temp2 = 0, 0 iL = 1.0 / L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 *iL) where x contains input samples, L is a number of points to be inserted, y will contain output samples. My question is how to implement such algorithm in ANSI C in a most effective way, e.g. is it possible to avoid the second loop? NOTE: presented Python code is just to understand how this algorithm works. UPDATE: here is an example how it works in Python: x=[] y=[] hold=[] num_points=20 points_inbetween = 2 temp1,temp2=0,0 for i in range(num_points): x.append( sin(i*2.0*pi * 0.1) ) L = points_inbetween iL = 1.0/L for i in x: hold = [i-temp1] * L temp1 = i for j in hold: temp2 += j y.append(temp2 * iL) Let's say x=[.... 10, 20, 30 ....]. Then, if L=1, it will produce [... 10, 15, 20, 25, 30 ...]

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  • How to make simple mathematical operations and displaying the result in a textbox

    - by Audel
    Hi, I know is a rather simple question but I just can't find an appropriate example in google or anywhere. I've got this piece int numberOfPlays = int.Parse(textBox2.Text); numberOfPlays = (numberOfPlays++); textBox2.Text = (numberOfPlays.ToString()); MessageBox.Show(numberOfPlays.ToString()); So basically what I want to do is to get the value of the textBox2, make it an integer and then add 1 to it. I can't think of any more details right now, so if i'm not clear enough please ask Thanks in advance

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  • Quaternion Cameras and projectile vectors

    - by Tom J Nowell
    In our software we have a camera based on mouse movement, and a quarternion at its heart. We want to fire projectiles from this position, which we can do, however we want to use the camera to aim. The projectile takes a vector which it will add to its position each game frame. How do we acquire such a vector from a given camera/quaternion?

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  • simple dividing

    - by dontoo
    Lets say I am dividing 2592 / 324 = 8 Practically I must guess that 324 goes 8 times in 2592 without reminder. For example, first I try with 7 ( 7*324 = 2268, reminder 324, so 7 is wrong, so I try with 8 and 8 is correct) Is there anyway to do dividing without guessing( trying ), like multiplication ( all mechanically, digit by digit )?

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  • Matlab - Find point of intersection between two vectors

    - by Silv3rSurf
    I have a very simple matlab question. What is the easiest way to find the point of intersection between two vectors. I am not familiar with the various matlab fuctions -- it seems like there should be one for this. For example if I have one vector from (0,0) to (6,6) and another vector from (0,6) to (6,0), I need to determine that they intersect at (3,3) Thanks.

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  • using context resource in gwt 2 hosted mode

    - by rafael
    Hello all, I am moving a web app from gwt 1.5 to gwt 2.0. I am trying to connect to the a database resource I have in my context.xml file.In gwt 1.5 I had set up root.xml in tomcat-conf-gwt-localhost. I have no idea where to set up the resource in GWT 2.0. I tried placing my context.xml file in war-META-INF with no luck. Anyone have an idea where to place the context.xml file to be able to use a jndi database resource in GWT 2.0? Thanks in advanced

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  • Uniforme distance between points

    - by Reonarudo
    Hello, How could I, having a path defined by several points that are not in a uniform distance from each other, redefine along the same path the same number of points but with a uniform distance. I'm trying to do this in Objective-C with NSArrays of CGPoints but so far I haven't had any luck with this. Thank you for any help. EDIT I was wondering if it would help to reduce the number of points, like when detecting if 3 points are collinear we could remove the middle one, but I'm not sure that would help.

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