Visual C++ Log Normal Distribution

This is a discussion on Visual C++ Log Normal Distribution within the C++ Programming forums, part of the General Programming Boards category; hey, now i using the Visual Studio 2010 C++ i would like to random generate a number from log normal ...

  1. #1
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    Visual C++ Log Normal Distribution

    hey, now i using the Visual Studio 2010 C++
    i would like to random generate a number from log normal distribution, but so far i only know to random generate a number from normal distribution by:

    rand() / rand_max

    rite???? then, i dont know how to do for log normal distribution...
    pls help me, tq

  2. #2
    - - - - - - - - oogabooga's Avatar
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    rand()/RAND_MAX does not give a "normal distribution". It is simply linear. Here are some ideas for a normal distribution.
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    Visual Studio 2010 has support for the <random> header, which is now part of the C++11 standard. <random> has support for lognormal distributions, among many other things; here's a quick example of its usage:

    Code:
    #include <random>
    #include <ctime>
    
    ...
    
    std::mt19937 randgen;
    randgen.seed(time(NULL));
    
    //the parameters are (mean, standard deviation) - default is (0.0, 1.0)
    std::lognormal_distribution<float> lognorm(0.0, 0.25);
    
    float result = lognorm(randgen);
    Last edited by bernt; 03-17-2012 at 04:36 PM. Reason: derped the code
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    Algorithm Dissector iMalc's Avatar
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    rand() / (double)RAND_MAX gives what is known as a "uniform distribution" because rand() is itself a uniform distribution.
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    Quote Originally Posted by bernt View Post
    Visual Studio 2010 has support for the <random> header, which is now part of the C++11 standard. <random> has support for lognormal distributions, among many other things; here's a quick example of its usage:

    Code:
    #include <random>
    #include <ctime>
    
    ...
    
    std::mt19937 randgen;
    randgen.seed(time(NULL));
    
    //the parameters are (mean, standard deviation) - default is (0.0, 1.0)
    std::lognormal_distribution<float> lognorm(0.0, 0.25);
    
    float result = lognorm(randgen);

    tq...it work so far....
    but if i want the number range from 3 to 200, how to do?
    bcz now i using lognorm(31.1, 0.48), but it result to me is too huge,
    tq

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    Quote Originally Posted by iMalc View Post
    rand() / (double)RAND_MAX gives what is known as a "uniform distribution" because rand() is itself a uniform distribution.


    so it is the same uniform distribution and what is the diff if i write so:

    x = rand()%4+1;

    and

    x = (rand()%4+1)/RAND_MAX;


    but for program with RAND_MAX, i oways get the value of 0, is it i written it wrong? or should i define the RAND_MAX 1st???

    tq very much for answer it

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