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Re: A conditional random number generation problem (please help me!)

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  • Subject: [mg66880] Re: A conditional random number generation problem (please help me!)
  • From: "mike" <mike at>
  • Date: Fri, 2 Jun 2006 04:09:12 -0400 (EDT)
  • References: <e1ijuv$3oh$>
  • Sender: owner-wri-mathgroup at

"rjmachado3" <rjmachado3 at> wrote in message 
news:e1ijuv$3oh$1 at
>I need to know the formula for the random function that return random
> numbers in a range of a and b integers [a,b] but that obey on a custom
> probability (possibly different!) for each integer number on this [a,b]
> range (of course the sum of all integer number probabilities are = 1!).
> Finally, what i want is the general function formula that simulate the
> random behavior (based on a custom probability value for each integer
> number between the [a,b] range. confuse? i hope not! please help me!!!!
> what i know so far is that the function formula for generating a "pure"
> random number between [a,b] range is:
> rand()*(b-a)+a
> where rand() return a random number between 0 and 1.

If I understand your problem correctly it is similar to one I have had to 

I have a vector with over 15 million integers in the range of -3500 to + 
3300.  Zero and +1 and -1 occur more often than +/- 2 which are more 
frequent than +/- 3 etc.   However some integers occur much more frequently 
than the next smaller value and there is no known function defining the 
frequency of all integers.

I need to be able to randomly generate arbitrary numbers of additional 
integers with the same frequency as found in the original vector.

I solved this by simply using the built-in random function to generate an 
index into the original vector and returned what ever value was found.

I hope this helps.

Mike Sicilian

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