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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 21, 2007 8:13 AM

On 21 Dec 2007 14:53:38 +0200, Phil Carmody
<thefatphil_demunged@yahoo.co.uk> wrote:

>quasi <quasi@null.set> writes:
>> On 21 Dec 2007 14:33:08 +0200, Phil Carmody
>> <thefatphil_demunged@yahoo.co.uk> wrote:
>>

>> >John <iamachamp@gmail.com> writes:
>> >> 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.

>> >
>> >int rand1to7i()
>> >{
>> > int r1=rand1to5i();
>> > if(r1==5) { r1+=rand1to5i()/2; }
>> > return r1;
>> >}

>>
>> Fatally flawed.

>
>Wrong. Care to back up your claim? Between you and me, I
>reckon you've not thought about my response enough.

Yes, do a simulation, and then _you_ think about it.

>> >double rand1to7d()
>> >{
>> > return rand1to5d()+(rand1to5d()-1)/2;
>> >}

>>
>> Inefficient -- uses 2 RNG calls, instead of 1.

>
>Wrong. If you stretch the numbers out, you'll leave gaps
>between them, these aren't actual reals, you did realise
>that, right? You *need* 2 calls to ensure that you leave
>no gaps.

Forget gaps -- your method is biased!

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