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

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quasi

Posts: 12,057
Registered: 7/15/05
Re: Random numbers
Posted: Dec 21, 2007 9:29 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

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.

>Please get your argument straight before posting nonsense to
>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
Read Random numbers
Champ
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Marshall
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Phil Carmody
12/21/07
Read Re: Random numbers
Marshall
12/21/07
Read Re: Random numbers
briggs@encompasserve.org
12/21/07
Read Re: Random numbers
William Elliot
12/21/07
Read Re: Random numbers
quasi
12/22/07
Read Re: Random numbers
William Elliot
12/21/07
Read Re: Random numbers
Pubkeybreaker
12/21/07
Read Re: Random numbers
b92057@yahoo.com
12/22/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
simple.popeye@gmail.com
12/21/07
Read Re: Random numbers
simple.popeye@gmail.com
12/22/07
Read Re: Random numbers
quasi
12/22/07
Read Re: Random numbers
Gib Bogle
12/22/07
Read Re: Random numbers
quasi
12/21/07
Read Re: Random numbers
Marshall
12/22/07
Read Re: Random numbers
simple.popeye@gmail.com
12/22/07
Read Re: Random numbers
quasi
12/22/07
Read Re: Random numbers
simple.popeye@gmail.com
12/22/07
Read Re: Random numbers
quasi
12/22/07
Read Re: Random numbers
quasi
12/22/07
Read Re: Random numbers
quasi
12/22/07
Read Re: Random numbers
simple.popeye@gmail.com
12/22/07
Read Re: Random numbers
quasi
12/23/07
Read Re: Random numbers
simple.popeye@gmail.com
12/23/07
Read Re: Random numbers
simple.popeye@gmail.com
12/23/07
Read Re: Random numbers
simple.popeye@gmail.com
12/23/07
Read Re: Random numbers
simple.popeye@gmail.com
12/23/07
Read Re: Random numbers
simple.popeye@gmail.com
12/22/07
Read Re: Random numbers
adder
12/22/07
Read Re: Random numbers
simple.popeye@gmail.com
12/22/07
Read Re: Random numbers
Herman Rubin
12/22/07
Read Re: Random numbers
adder
12/22/07
Read Re: Random numbers
b92057@yahoo.com
12/22/07
Read Re: Random numbers
quasi
12/23/07
Read Re: Random numbers
b92057@yahoo.com
12/23/07
Read Re: Random numbers
quasi
12/23/07
Read Re: Random numbers
b92057@yahoo.com
12/24/07
Read Re: Random numbers
quasi
12/24/07
Read Re: Random numbers
quasi
12/24/07
Read Re: Random numbers
adder
12/24/07
Read Re: Random numbers
quasi
12/24/07
Read Re: Random numbers
adder
12/24/07
Read Re: Random numbers
b92057@yahoo.com

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