Random Numbers

This is a discussion on Random Numbers within the C Programming forums, part of the General Programming Boards category; Hi, I have written a program that uses the random number generator function from the GNU scientific library. Every time ...

  1. #1
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    Random Numbers

    Hi,

    I have written a program that uses the random number generator function from the GNU scientific library.
    Every time I execute the program it generates the same random numbers. Is there anyway I can generate different random number every time I execute the program.

    Thanks
    Vibhuti

  2. #2
    C++ Witch laserlight's Avatar
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    You probably need to seed the random number generator with a different seed.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Officially An Architect brewbuck's Avatar
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    To go even further, you could provide a way for the user to specify the seed, either as a command line argument, environment variable, or something else. That way, the user can reproduce a result if they want to.

    (It also makes debugging less impossible if you have a way to reproduce the seed)
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Most random number generators work on a seed. In the normal C library random generator, that's srand(). I don't know what it's called in GSL, but google finds this:
    http://www.gnu.org/software/gsl/manu...alization.html

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Thank you!! Changing the seed works

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    I have the same problem.
    But i do not understand how u change the seed

    can someone please give me more info on that
    im still very new to C. :-)

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    C++ Witch laserlight's Avatar
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    Quote Originally Posted by cursedninja
    But i do not understand how u change the seed
    According to the documentation that matsp linked to, it is by using the gsl_rng_set() function. Have you tried using it? (Or if you are talking about the C standard library's rand() function, it will be srand(), also mentioned by matsp.)
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    I did not understand much about the gsl_rng_set() function.

    i am using the standard library function.
    How do i change the seed for the srand?

    could u just show me what code i should use?

  9. #9
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by cursedninja
    i am using the standard library function.
    How do i change the seed for the srand?
    Read this article on using rand().
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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    Smile

    thank you very much.

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