On Wed, Apr 15, 2009 at 12:34 PM, Peter Castine <pcast...@gmx.net> wrote:
> On 14-Apr-2009, at 22:32, Eric E. Dolecki wrote:
>>
>> int result = (arc4random()%9) + 1;
>>
>> if (result >= activeTarget) ++result;
>>
>> activeTarget = result;
>>
>> That seems a little odd to me to do things that way - but I'm not really
>> sure.
>
> This will give you biased results. Instead of equally distributed values in
> {1, 2,.. 10}, you will only get 10 just over 1.2% of the time and 1 a bit
> under the expected 10%, with the other values taking up the slack.
> Additionally, the absolute differences of consecutive values will not be
> equally distributed. There will be a skew towards sequences where x(n+1) =
> x(n) + 1. The second point may or may not be a problem for a game whereas
> the first point is probably too deadly even for a game.No it won't. The first line generates numbers in the range [1,9], evenly distributed (ignoring the very small modulo bias). The second line shifts the end of the range so that the number now falls into either [1,activeTarget) or (activeTarget, 10]. It is still evenly distributed in those two ranges. > The following would deal with the first point: > > int result = myRandomNumberGenerator() % 10 + 1; > if (result == activeTarget) > result = result % 10 + 1; > activeTarget = result; This one has a massive flaw in that it will produce (activeTarget+1)%10 20% of the time and produce the other numbers only 10% of the time. Do we really need One Thousand Ways To Be Wrong About Random Numbers? The OP described a perfectly good technique for this in his *original post to this thread*. Mike _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
