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

 Messages: [ Previous | Next ]
 Phil Carmody Posts: 2,219 Registered: 12/7/04
Re: Random numbers
Posted: Dec 21, 2007 9:40 AM

quasi <quasi@null.set> writes:
> On Fri, 21 Dec 2007 08:13:37 -0500, quasi <quasi@null.set> wrote:
>

> >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!

>
> Ok, your method for the real case is not biased -- sorry.

Gawd, don't apologise for that. It's horribly biased, and
I don't care. In fact gGaps are in fact nothing but bias -
P(x : x \in gap) = 0.

Well duh! You don't think that was deliberate, do you?

Phil
--
Dear aunt, let's set so double the killer delete select all.
-- Microsoft voice recognition live demonstration

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