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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 9:29 AM

On 21 Dec 2007 16:16:52 +0200, Phil Carmody
<thefatphil_demunged@yahoo.co.uk> wrote:

>quasi <quasi@null.set> writes:
>> On Fri, 21 Dec 2007 07:43:48 -0500, quasi <quasi@null.set> wrote:
>>

>> >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.
>> >

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

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

>>
>> Forget inefficiency -- it's worse than that.
>>
>> It's biased.

>
>Since when what being unbiased in the requirements?

Don't be ridiculous.

Unbiased was surely implied.

>> >>> 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.

>
>I'm really trying hard, but I just can't see any mention
>of the required distribution at all. Can you?

If that was the case, then your method is even more inefficient.

A simpler method for both the real case and the integer case would be
to always return the number 3. Alternatively, call the random number
generator for the range 1 to 5 and return _that_ value.

Of course it was implicit in the problem that unbiased results were
required.

For the case of reals, you wouldn't have talked about gaps if you
weren't trying to avoid lack of uniformity.

>Usenet, I always do.

Your current response is cop-out, and you know it.

Admit your errors, don't try to obscure them -- that would show some
integrity.

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