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01252012, 04:32 PM #1
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Generating a random number taken from a normal distribution
Hello,
I need help creating a function in javascript that produces random numbers generated from a normal curve distribution with a mean and standard deviation that I can specify (and easily change). I would like only whole numbers and the ability to set reasonable maximum and minimums.
Thanks,
Adrian

01252012, 06:36 PM #2
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Code:<script type = "text/javascript"> function rnd_snd() { return (Math.random()*21)+(Math.random()*21)+(Math.random()*21); } // Three random numbers between 1 and 1 added together. That will give a normal distribution with mean = 0 and standard deviation = 1. // The function will return a decimal with an average value of 0. function rnd(mean, stdev) { return Math.round(rnd_snd()*stdev + mean); } // Multiply the result by the standard deviation that you want, then add your desired mean. alert (rnd(38,2)) // mean, standard deviation </script>
All advice is supplied packaged by intellectual weight, and not by volume. Contents may settle slightly in transit.Last edited by Philip M; 01252012 at 06:51 PM.
All the code given in this post has been tested and is intended to address the question asked.
Unless stated otherwise it is not just a demonstration.

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01262012, 05:06 PM #3
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The computer is always right. The computer is always right. The computer is always right. Take it from someone who has programmed for over ten years: not once has the computational mechanism of the machine malfunctioned.André Behrens, NY Times Software Developer

01262012, 08:26 PM #4
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Not quite sure what you mean, but all I have done here is added three random numbers between 1 and 1 together. That will give a point (almost +3 to almost 3) on a normal distribution with mean = 0 and standard deviation = 1. This is also called standard normal distribution. Try it yourself:
Code:<script type = "text/javascript"> var tot = 0; var its = 500; // iterations for (var i = 0; i<its; i++) { var randy = (Math.random()*21)+(Math.random()*21)+(Math.random()*21); tot += randy; document.write(randy); document.write("<br>") } alert (tot/its); // close to zero, especially if the number of iterations is increased to (say) 10000 </script>
Last edited by Philip M; 01262012 at 09:04 PM.
All the code given in this post has been tested and is intended to address the question asked.
Unless stated otherwise it is not just a demonstration.

01262012, 11:08 PM #5
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The computer is always right. The computer is always right. The computer is always right. Take it from someone who has programmed for over ten years: not once has the computational mechanism of the machine malfunctioned.André Behrens, NY Times Software Developer

02032012, 10:43 PM #6
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Thank you! Very useful, and I will have a play around with it soon.
Now things get a little more tricky: What about a chi square distribution (with 3 degrees of freedom)?
Cheers,
Adrian

02042012, 08:32 AM #7
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Well, what about it? Google to find for example
http://www.fourmilab.ch/rpkp/experim...s/chiCalc.html
All the code given in this post has been tested and is intended to address the question asked.
Unless stated otherwise it is not just a demonstration.

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