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Topic: Random numbers
Replies: 64   Last Post: Dec 24, 2007 1:04 PM

 Messages: [ Previous | Next ]
 quasi Posts: 12,067 Registered: 7/15/05
Re: Random numbers
Posted: Dec 22, 2007 1:51 PM

On Sat, 22 Dec 2007 10:43:27 -0800 (PST), vr <simple.popeye@gmail.com>
wrote:

>On Dec 22, 11:35 pm, quasi <qu...@null.set> wrote:
>> On Sat, 22 Dec 2007 10:32:37 -0800 (PST), vr <simple.pop...@gmail.com>
>> wrote:
>>
>>
>>
>>
>>

>> >On Dec 22, 11:16 pm, quasi <qu...@null.set> wrote:
>> >> On Fri, 21 Dec 2007 10:57:00 -0800 (PST), simple.pop...@gmail.com
>> >> wrote:

>>
>> >> >On Dec 21, 11:37 pm, bill <b92...@yahoo.com> wrote:
>> >> >> On Dec 21, 3:16 am, John <iamach...@gmail.com> wrote:
>>
>> >> >> > Given a function that returns a random number between 1-5, write one
>> >> >> > that returns a random number between 1-7 for the case when it should
>> >> >> > be integer and for the case it can be real.

>>
>> >> >> Let S be the function that generates a RN between 1 and 5.  Then
>>
>> >> >> T =  S_1 + S_2 + ... + S_7
>>
>> >> >> For the reals , RN_7 = T/7
>>
>> >> >May be this should fix it:
>>
>> >> >For the reals , RN_7 = 1 + (T-7)*3/14
>>
>> >> Yes, that fixes the range.
>>
>> >> But it's still biased (that is, not a unform distribution).
>>
>> >> quasi- Hide quoted text -
>>
>> >> - Show quoted text -
>>
>> >Hmm. Let me simplify it:
>>
>> >RN_7 = T*3/14 - 0.5
>>
>> >If you look at T*3/14, it just scales the sum of random numbers
>> >uniformly using a constant multiplier. Did I miss to notice any non-
>> >uniformity here?

>>
>> Yes, T is not uniformly distributed in its range.

>
>Ok. But if S_n is guaranted to be uniformly distributed in the range 1
>to 5, then doesn't it mean the sum of 7 such numbers will also get
>distributed over 7 to 35? I'm just curious. Thanks.

Yes, but not uniformly.

What's the chance of getting exactly 35?

If it was a uniform distributioon it would be 1/29, right?

quasi

Date Subject Author
12/21/07 Champ
12/21/07 quasi
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 Marshall
12/21/07 Phil Carmody
12/21/07 quasi
12/21/07 Phil Carmody
12/21/07 Marshall
12/21/07 briggs@encompasserve.org
12/21/07 William Elliot
12/21/07 quasi
12/22/07 William Elliot
12/21/07 Pubkeybreaker
12/21/07 b92057@yahoo.com
12/22/07 quasi
12/21/07 simple.popeye@gmail.com
12/21/07 simple.popeye@gmail.com
12/22/07 quasi
12/22/07 Gib Bogle
12/22/07 quasi
12/21/07 Marshall
12/22/07 simple.popeye@gmail.com
12/22/07 quasi
12/22/07 simple.popeye@gmail.com
12/22/07 quasi
12/22/07 quasi
12/22/07 quasi
12/22/07 simple.popeye@gmail.com
12/22/07 quasi
12/23/07 simple.popeye@gmail.com
12/23/07 simple.popeye@gmail.com
12/23/07 simple.popeye@gmail.com
12/23/07 simple.popeye@gmail.com
12/23/07 simple.popeye@gmail.com
12/22/07 simple.popeye@gmail.com
12/22/07 Herman Rubin
12/22/07 b92057@yahoo.com
12/22/07 quasi
12/23/07 b92057@yahoo.com
12/23/07 quasi
12/23/07 b92057@yahoo.com
12/24/07 quasi
12/24/07 quasi
12/24/07 quasi
12/24/07 b92057@yahoo.com